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Associate Professor Martina Doblin


My research interests include algal ecology, marine biogeochemistry and biological oceanography.

Specifically, I am interested in:

  • Processes involved in algal bloom formation and phytoplankton community assembly;
  • Measuring the functional traits of living marine eukaryotes to improve our understanding of their role in marine ecosystems;
  • The physiological and adaptive capacity of algae under different selection regimes;
  • Relating in situ observations of photosynthetic microbes to satellite products for improved ocean observing and modelling.

At UTS, working within C3's Aquatic Processes Group and leading COAST, I hope to contribute important knowledge needed to address Australia's grand challenges of food security, biodiversity conservation and ecosystem health and climate variability and change.


  • Node leader, NSW Integrated Marine Observing System (IMOS)

  • Convenor, IMOS Bio-optical Working Group

  • Marine National Facility Chief Scientist

Climate Change Report Card
Update from the East Australian Current
Eddies and the East Australian Current

Image of Martina Doblin
Associate Professor, Plant Functional Biology & Climate Change
Associate Member, Centre for Technology in Water and Wastewater
Core Member, Plant Functional Biology & Climate Change
BSc(Hon), PhD
+61 2 9514 8307

Research Interests

  • diversity and functioning of coastal phytoplankton influenced by the East Australia Current
  • development of cyanobacterial blooms in freshwater reservoirs
  • impact and management of invasive marine species

Researcher ID: E-8719-2013
Google Scholar
Research Gate

Can supervise: Yes

  • Lecturer in Marine Communities (91157)
  • Lecturer in Management of Coasts, Oceans & Catchments (98711)
  • Lecturer in Environmental Management (91122)


Sinutok, S., Hill, R., Doblin, M.A. & Ralph, P.J. 2010, 'Rising ocean temperature and ocean acidification will reduce productivity and calcification in Halimeda sp. and benthic foraminifera from the Great Barrier Reef', Euro ISRS Symposium 2010, Grafisch Service Center, Wageningen, The Netherlands, pp. 191-191.
Schrameyer, V., Kraemer, W., Hill, R., Doblin, M.A., Kai, B. & Ralph, P.J. 2010, 'Nutritional status of hard and soft corals influences photosynthesis capacity of Symbiodinium sp. and vitality of the holobiont', Euro ISRS Symposium 2010, Grafisch Service Center, Wageningen, The Netherlands, pp. 108-108.
Petrou, K., Doblin, M.A., Hassler, C.S. & Ralph, P.J. 2009, 'Multiple stressors on the sea ice diatom Fragilariopsis cylindrus - photophysiological impacts of seasonal freezing and melting of sea ice', Japan.
Doblin, M.A., Ralph, P.J., Oubelkheir, K., Hassler, C.S., Suthers, I. & Thompson, P. 2009, 'Using IMOS to bridge the gap between direct measurements of marine primary production and models', Adelaide, Australia.
Petrou, K., Shelly, K., Hassler, C.S., Schoemann, V., Doblin, M.A. & Ralph, P.J. 2007, 'Ocean productivity in a changing world: Iron-limitation of Southern Ocean phytoplankton and implication for Antarctic meltwater productivity', Australia.

Journal articles

Sackett, O., Petrou, K., Reedy, B., Hill, R., Doblin, M., Beardall, J., Ralph, P. & Heraud, P. 2016, 'Snapshot prediction of carbon productivity, carbon and protein content in a Southern Ocean diatom using FTIR spectroscopy', ISME Journal, vol. 10, no. 2, pp. 416-426.
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© 2016 International Society for Microbial Ecology All rights reserved. Diatoms, an important group of phytoplankton, bloom annually in the Southern Ocean, covering thousands of square kilometers and dominating the region's phytoplankton communities. In their role as the major food source to marine grazers, diatoms supply carbon, nutrients and energy to the Southern Ocean food web. Prevailing environmental conditions influence diatom phenotypic traits (for example, photophysiology, macromolecular composition and morphology), which in turn affect the transfer of energy, carbon and nutrients to grazers and higher trophic levels, as well as oceanic biogeochemical cycles. The paucity of phenotypic data on Southern Ocean phytoplankton limits our understanding of the ecosystem and how it may respond to future environmental change. Here we used a novel approach to create a 'snapshot' of cell phenotype. Using mass spectrometry, we measured nitrogen (a proxy for protein), total carbon and carbon-13 enrichment (carbon productivity), then used this data to build spectroscopy-based predictive models. The models were used to provide phenotypic data for samples from a third sample set. Importantly, this approach enabled the first ever rate determination of carbon productivity from a single time point, circumventing the need for time-series measurements. This study showed that Chaetoceros simplex was less productive and had lower protein and carbon content during short-term periods of high salinity. Applying this new phenomics approach to natural phytoplankton samples could provide valuable insight into understanding phytoplankton productivity and function in the marine system.
Jeffries, T.C., Curlevski, N.J., Brown, M.V., Harrison, D.P., Doblin, M.A., Petrou, K., Ralph, P.J. & Seymour, J.R. 2016, 'Partitioning of fungal assemblages across different marine habitats.', Environ Microbiol Rep.
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Fungi are a highly diverse group of microbes that fundamentally influence the biogeochemistry of the biosphere, but we currently know little about the diversity and distribution of fungi in aquatic habitats. Here we describe shifts in marine fungal community composition across different marine habitats, using targeted pyrosequencing of the fungal ITS region. Our results demonstrate strong partitioning of fungal community composition between estuarine, coastal and oceanic samples, with each habitat hosting discrete communities that are controlled by patterns in salinity, temperature, oxygen and nutrients. While estuarine habitats comprised a significant proportion of fungal groups often found in terrestrial habitats, the open ocean sites were dominated by previously unidentified groups. The patterns observed here indicate that fungi are potentially a significant, although largely overlooked, feature of the ocean's microbiota, but greater efforts to characterise marine species are required before the full ecological and biogeochemical importance of marine fungi can be ascertained.
Jones, E.M., Doblin, M.A., Matear, R. & King, E. 2015, 'Assessing and evaluating the ocean-colour footprint of a regional observing system', Journal of Marine Systems, vol. 143, pp. 49-61.
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© 2014. A recurring problem with point based marine observations is how to scale them up to infer local and regional dynamics, this is especially true of biogeochemical (BGC) variables such as chlorophyll-a (Chl-a) and dissolved inorganic nutrients. The recent study by Oke and Sakov (2012) uses a combination of historical satellite imagery, and numerical model output to assess the footprint of physical variables in regional observing system. However, in the absence of long integrations of marine biogeochemical models, there are very few tools to interpret the biological dynamics that may be captured by a regional observing system. In this study, a generic approach to assess the biological footprint of regional observing systems is developed. We used the recently reprocessed gridded chlorophyll-a product (NASA OC3M algorithm) to estimate the spatial footprint of the biological observations of the Australian Integrated Marine Observing System (IMOS) National Reference Station (NRS) network at intra-weekly, intra-monthly and intra-seasonal timescales. From this analysis, it is clear that the NRSs are only able to characterize variability at locations close (typically within 9-50. km) to the NRS sites at weekly timescales. However, at monthly and seasonal timescales, the NRS footprint is large enough to infer shelf and regional scale dynamics that are representative of substantial portions of the Australian shelf. This is a generic method that can be incorporated into the design and evaluation of regional observing systems where gridded ocean colour products are available.
Hassler, C.S., Norman, L., Mancuso Nichols, C.A., Clementson, L.A., Robinson, C., Schoemann, V., Watson, R.J. & Doblin, M.A. 2015, 'Iron associated with exopolymeric substances is highly bioavailable to oceanic phytoplankton', Marine Chemistry, vol. 173, pp. 136-147.
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&copy; 2014 Elsevier B.V. Growth limitation of marine algae due to lack of iron occurs in up to 40% of the global ocean. Despite important advances on the impact of organic compounds on iron biogeochemistry, their roles in controlling iron availability to prokaryotic and eukaryotic phytoplankton remain unclear. Whether algal and bacterial exopolymeric substances (EPS) include organic ligands which may help iron-limited phytoplankton growth remains an unknown. If so, then EPS could relieve phytoplankton iron limitation with implications for the biological carbon pump and hence the regulation of atmospheric CO<inf>2</inf>. Here we compared the biological impact of algal, bacterial and in situ EPS with model compounds, a siderophore and two saccharides on biological parameters including, iron bioavailability, phytoplankton growth, photo-physiology and community structure. Laboratory and field experiments demonstrated that EPS produced by marine microorganisms are efficient in sustaining biological iron uptake as well as algal growth, and can affect natural phytoplankton community structure. Our data suggest that natural phytoplankton growth enhancement in the presence of EPS was not solely due to highly bioavailable iron forms, but also because EPS contains other micronutrients. Stronger ligands were detected following iron-siderophore enrichments (log K<inf>Fe'L</inf>=12.0) and weaker ligands were measured in the presence of EPS (log K<inf>Fe'L</inf>=10.4-11.0). The trend of the conditional stability constants of organic ligands did not seem to be affected as a result of biological activity and photo-chemistry during our four day incubations. The shift in the phytoplankton community observed during our field experiments was not uniformly observed between different sites rendering it difficult to extrapolate which functional group(s) would benefit the most from iron bound to EPS.
Everett, J.D. & Doblin, M.A. 2015, 'Characterising primary productivity measurements across a dynamic western boundary current region', Deep-Sea Research Part I: Oceanographic Research Papers, vol. 100, pp. 105-116.
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&copy; 2015 Elsevier Ltd. Determining the magnitude of primary production (PP) in a changing ocean is a major research challenge. Thousands of estimates of marine PP exist globally, but there remain significant gaps in data availability, particularly in the Southern Hemisphere. In situ PP estimates are generally single-point measurements and therefore we rely on satellite models of PP in order to scale up over time and space. To reduce the uncertainty around the model output, these models need to be assessed against in situ measurements before use. This study examined the vertically-integrated productivity in four water-masses associated with the East Australian Current (EAC), the major western boundary current (WBC) of the South Pacific. We calculated vertically integrated PP from shipboard <sup>14</sup>C PP estimates and then compared them to estimates from four commonly used satellite models (ESQRT, VGPM, VGPM-Eppley, VGPM-Kameda) to assess their utility for this region. Vertical profiles of the water-column show each water-mass had distinct temperature-salinity signatures. The depth of the fluorescence-maximum (f<inf>max</inf>) increased from onshore (river plume) to offshore (EAC) as light penetration increased. Depth integrated PP was highest in river plumes (792&plusmn;181mgCm<sup>-2</sup>d<sup>-1</sup>) followed by the EAC (534&plusmn;116mgCm<sup>-2</sup>d<sup>-1</sup>), continental shelf (140&plusmn;47mgCm<sup>-2</sup>d<sup>-1</sup>) and cyclonic eddy waters (121&plusmn;4mgCm<sup>-2</sup>d<sup>-1</sup>). Surface carbon assimilation efficiency was greatest in the EAC (301&plusmn;145mgC (mgChl-a)<sup>-1</sup>d<sup>-1</sup>) compared to other water masses. All satellite primary production models tested underestimated EAC PP and overestimated continental shelf PP. The ESQRT model had the highest skill and lowest bias of the tested models, providing the best first-order estimates of PP on the continental shelf, including at a coastal time-series station, Port Hacking, which showed considerable inte...
Tian, C., Pei, H., Hu, W., Hao, D., Doblin, M.A., Ren, Y., Wei, J. & Feng, Y. 2015, 'Variation of phytoplankton functional groups modulated by hydraulic controls in Hongze Lake, China', Environmental Science and Pollution Research, vol. 22, no. 22, pp. 18163-18175.
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&copy; 2015, Springer-Verlag Berlin Heidelberg. Hongze Lake is a large, shallow, polymictic, eutrophic lake in the eastern China. Phytoplankton functional groups in this lake were investigated from March 2011 to February 2013, and a comparison was made between the eastern, western, and northern regions. The lake shows strong fluctuations in water level caused by monsoon rains and regular hydraulic controls. By application of the phytoplankton functional group approach, this study aims to investigate the spatial and temporal dynamics and analyze their influencing factors. Altogether, 18 functional groups of phytoplankton were identified, encompassing 187 species. In order to seek the best variable describing the phytoplankton functional group distribution, 14 of the groups were analyzed in detail using redundancy analysis. Due to the turbid condition of the lake, the dominant functional groups were those tolerant of low light. The predominant functional groups in the annual succession were D (Cyclotella spp. and Synedra acus), T (Planctonema lauterbornii), P (Fragilaria crotonensis), X1 (Chlorella vulgaris and Chlorella pyrenoidosa), C (Cyclotella meneghiniana and Cyclotella ocellata), and Y (Cryptomonas erosa). An opposite relationship between water level and the biomass of predominant groups was observed in the present study. Water level fluctuations, caused by monsoonal climate and artificial drawdown, were significant factors influencing phytoplankton succession in Hongze Lake, since they alter the hydrological conditions and influence light and nutrient availability. The clearly demonstrated factors, which significantly influence phytoplankton dynamics in Hongze Lake, will help government manage the large shallow lakes with frequent water level fluctuations.
Henschke, N., Everett, J.D., Suthers, I.M., Smith, J.A., Hunt, B.P.V., Doblin, M.A. & Taylor, M.D. 2015, 'Zooplankton trophic niches respond to different water types of the western Tasman Sea: A stable isotope analysis', Deep-Sea Research Part I: Oceanographic Research Papers, vol. 104, pp. 1-8.
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&copy; 2015 Elsevier Ltd. The trophic relationships of 21 species from an oceanic zooplankton community were studied using stable isotopes of carbon and nitrogen. Zooplankton and suspended particulate organic matter (POM) were sampled in three different water types in the western Tasman Sea: inner shelf (IS), a cold core eddy (CCE) and a warm core eddy (WCE). ?<sup>15</sup>N values ranged from 3.9&#8240; for the parasitic copepod Sapphirina augusta to 10.2&#8240; for the euphausiid, Euphausia spinifera. ?<sup>13</sup>C varied from -22.6 to -19.4&#8240; as a result of the copepod Euchirella curticauda and E. spinifera. The isotopic composition of POM varied significantly among water types; as did the trophic enrichment of zooplankton over POM, with the lowest enrichment in the recently upwelled IS water type (0.5&#8240;) compared to the warm core eddy (1.6&#8240;) and cold core eddy (2.7&#8240;). The WCE was an oligotrophic environment and was associated with an increased trophic level for omnivorous zooplankton (copepods and euphausiids) to a similar level as carnivorous zooplankton (chaetognaths). Therefore carnivory in zooplankton can increase in response to lower abundance and reduced diversity in their phytoplankton and protozoan prey. Trophic niche width comparisons across three zooplankton species: the salp Thalia democratica, the copepod Eucalanus elongatus and the euphausiid Thysanoessa gregaria, indicated that both niche partitioning and competition can occur within the zooplankton community. We have shown that trophic relationships among the zooplankton are dynamic and respond to different water types. The changes to the zooplankton isotopic niche, however, were still highly variable as result of oceanographic variation within water types.
Messer, L.F., Mahaffey, C., M Robinson, C., Jeffries, T.C., Baker, K.G., Bibiloni Isaksson, J., Ostrowski, M., Doblin, M.A., Brown, M.V. & Seymour, J.R. 2015, 'High levels of heterogeneity in diazotroph diversity and activity within a putative hotspot for marine nitrogen fixation', ISME Journal.
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&copy; 2015 International Society for Microbial Ecology Australia's tropical waters represent predicted 'hotspots' for nitrogen (N2) fixation based on empirical and modelled data. However, the identity, activity and ecology of diazotrophs within this region are virtually unknown. By coupling DNA and cDNA sequencing of nitrogenase genes (nifH) with size-fractionated N2 fixation rate measurements, we elucidated diazotroph dynamics across the shelf region of the Arafura and Timor Seas (ATS) and oceanic Coral Sea during Austral spring and winter. During spring, Trichodesmium dominated ATS assemblages, comprising 60% of nifH DNA sequences, while Candidatus Atelocyanobacterium thalassa (UCYN-A) comprised 42% in the Coral Sea. In contrast, during winter the relative abundance of heterotrophic unicellular diazotrophs (?-proteobacteria and ?-24774A11) increased in both regions, concomitant with a marked decline in UCYN-A sequences, whereby this clade effectively disappeared in the Coral Sea. Conservative estimates of N2 fixation rates ranged from <1 to 91?nmol?l-1?day-1, and size fractionation indicated that unicellular organisms dominated N2 fixation during both spring and winter, but average unicellular rates were up to 10-fold higher in winter than in spring. Relative abundances of UCYN-A1 and ?-24774A11 nifH transcripts negatively correlated to silicate and phosphate, suggesting an affinity for oligotrophy. Our results indicate that Australia's tropical waters are indeed hotspots for N2 fixation and that regional physicochemical characteristics drive differential contributions of cyanobacterial and heterotrophic phylotypes to N2 fixation.The ISME Journal advance online publication, 27 November 2015; doi:10.1038/ismej.2015.205.
Johnston, E.L., Mayer-Pinto, M., Hutchings, P.A., Marzinelli, E.M., Ahyong, S.T., Birch, G., Booth, D.J., Creese, R.G., Doblin, M.A., Figueira, W., Gribben, P.E., Pritchard, T., Roughan, M., Steinberg, P.D. & Hedge, L.H. 2015, 'Sydney Harbour: What we do and do not know about a highly diverse estuary', Marine and Freshwater Research, vol. 66, no. 12, pp. 1073-1087.
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&copy; 2015 CSIRO. Sydney Harbour is a global hotspot for marine and estuarine diversity. Despite its social, economic and biological value, the available knowledge has not previously been reviewed or synthesised. We systematically reviewed the published literature and consulted experts to establish our current understanding of the Harbour's natural systems, identify knowledge gaps, and compare Sydney Harbour to other major estuaries worldwide. Of the 110 studies in our review, 81 focussed on ecology or biology, six on the chemistry, 10 on geology and 11 on oceanography. Subtidal rocky reef habitats were the most studied, with a focus on habitat forming macroalgae. In total 586 fish species have been recorded from the Harbour, which is high relative to other major estuaries worldwide. There has been a lack of process studies, and an almost complete absence of substantial time series that constrains our capacity to identify trends, environmental thresholds or major drivers of biotic interactions. We also highlight a lack of knowledge on the ecological functioning of Sydney Harbour, including studies on microbial communities. A sound understanding of the complexity, connectivity and dynamics underlying ecosystem functioning will allow further advances in management for the Harbour and for similarly modified estuaries around the world.
Mayer-Pinto, M., Johnston, E.L., Hutchings, P.A., Marzinelli, E.M., Ahyong, S.T., Birch, G., Booth, D.J., Creese, R.G., Doblin, M.A., Figueira, W., Gribben, P.E., Pritchard, T., Roughan, M., Steinberg, P.D. & Hedge, L.H. 2015, 'Sydney Harbour: A review of anthropogenic impacts on the biodiversity and ecosystem function of one of the world's largest natural harbours', Marine and Freshwater Research, vol. 66, no. 12, pp. 1088-1105.
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&copy; 2015 CSIRO. Sydney Harbour is a hotspot for diversity. However, as with estuaries worldwide, its diversity and functioning faces increasing threats from urbanisation. This is the first synthesis of threats and impacts in Sydney Harbour. In total 200 studies were reviewed: 109 focussed on contamination, 58 on habitat modification, 11 addressed non-indigenous species (NIS) and eight investigated fisheries. Metal concentrations in sediments and seaweeds are among the highest recorded worldwide and organic contamination can also be high. Contamination is associated with increased abundances of opportunistic species, and changes in benthic community structure. The Harbour is also heavily invaded, but invaders' ecological and economic impacts are poorly quantified. Communities within Sydney Harbour are significantly affected by extensive physical modification, with artificial structures supporting more NIS and lower diversity than their natural equivalents. We know little about the effects of fishing on the Harbour's ecology, and although ocean warming along Sydney is among the fastest in the world, we know little about how the ecosystem will respond to warming. The interactive and cumulative effects of stressors on ecosystem functioning and services in the Harbour are largely unknown. Sustainable management of this iconic natural system requires that knowledge gaps are addressed and translated into coherent environmental plans.
Sinutok, S., Hill, R., Kühl, M., Doblin, M.A. & Ralph, P.J. 2014, 'Ocean acidification and warming alter photosynthesis and calcification of the symbiont-bearing foraminifera Marginopora vertebralis', Marine Biology, vol. 161, no. 9, pp. 2143-2154.
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The impact of elevated CO2 and temperature on photosynthesis and calcification in the symbiont-bearing benthic foraminifer Marginopora vertebralis was studied. Individual specimens of M. vertebralis were collected from Heron Island on the southern Great Barrier Reef (Australia). They were maintained for 5 weeks at different temperatures (28, 32 &deg;C) and pCO2 (400, 1,000 ?atm) levels spanning a range of current and future climate-change scenarios. The photosynthetic capacity of M. vertebralis was measured with O2 microsensors and a pulse-amplitude-modulated chlorophyll (Chl) fluorometer, in combination with estimates of Chl a and Chl c 2 concentrations and calcification rates. After 5 weeks, control specimens remained unaltered for all parameters. Chlorophyll a concentrations significantly decreased in the specimens at 1,000 ?atm CO2 for both temperatures, while no change in Chl c 2 concentration was observed. Photoinhibition was observed under elevated CO2 and temperature, with a 70-80 % decrease in the maximum quantum yield of PSII. There was no net O2 production at elevated temperatures in both CO2 treatments as compared to the control temperature, supporting that temperature has more impact on photosynthesis and O2 flux than changes in ambient CO2. Photosynthetic pigment loss and a decrease in photochemical efficiency are thus likely to occur with increased temperature. The elevated CO2 and high temperature treatment also lead to a reduction in calcification rate (from +0.1 to >-0.1 % day-1). Thus, both calcification and photosynthesis of the major sediment-producing foraminifer M. vertebralis appears highly vulnerable to elevated temperature and ocean acidification scenarios predicted in climate-change models. &copy; 2014 Springer-Verlag Berlin Heidelberg.
Henschke, N., Everett, J.D., Doblin, M.A., Pitt, K.A., Richardson, A.J. & Suthers, I.M. 2014, 'Demography and interannual variability of salp swarms (Thalia democratica)', Marine Biology, vol. 161, no. 1, pp. 149-163.
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Swarms of the pelagic tunicate, Thalia democratica, form during spring, but the causes of the large interannual variability in the magnitude of salp swarms are unclear. Changes in asexual reproduction (buds per chain) of T. democratica populations in the coastal waters of south-east Australia (32-35&deg;S) were observed in three austral springs (October 2008-2010). T. democratica abundance was significantly higher in 2008 (1,312 individuals m-3) than 2009 and 2010 (210 and 92 individuals m-3, respectively). There was a significant negative relationship (linear regression, r 2 = 0.61, F 1,22 = 33.83, P < 0.001) between abundance and asexual reproduction. Similarly, relative growth rates declined with decreasing abundance. Generalised additive mixed modelling showed that T. democratica abundance was significantly positively related to preferred food >2 ?m in size (P < 0.05) and negatively related to the proportion of non-salp zooplankton (P < 0.001). Salp swarm magnitude, growth, and asexual reproduction may depend on the abundance of larger phytoplankton (prymnesiophytes and diatoms) and competition with other zooplankton. &copy; 2013 Springer-Verlag Berlin Heidelberg.
Hassler, C.S., Ridgway, K.R., Bowie, A.R., Butler, E.C.V., Clementson, L.A., Doblin, M.A., Davies, D.M., Law, C., Ralph, P.J., Van Der Merwe, P., Watson, R. & Ellwood, M.J. 2014, 'Primary productivity induced by iron and nitrogen in the Tasman Sea: An overview of the PINTS expedition', Marine and Freshwater Research, vol. 65, no. 6, pp. 517-537.
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The Tasman Sea and the adjacent subantarctic zone (SAZ) are economically important regions, where the parameters controlling the phytoplankton community composition and carbon fixation are not yet fully resolved. Contrasting nutrient distributions, as well as phytoplankton biomass, biodiversity and productivity were observed between the North Tasman Sea and the SAZ. In situ photosynthetic efficiency (FV/FM), dissolved and particulate nutrients, iron biological uptake, and nitrogen and carbon fixation were used to determine the factor-limiting phytoplankton growth and productivity in the North Tasman Sea and the SAZ. Highly productive cyanobacteria dominated the North Tasman Sea. High atmospheric nitrogen fixation and low nitrate dissolved concentrations indicated that non-diazotroph phytoplankton are nitrogen limited. Deck-board incubations also suggested that, at depth, iron could limit eukaryotes, but not cyanobacteria in that region. In the SAZ, the phytoplankton community was dominated by a bloom of haptophytes. The low productivity in the SAZ was mainly explained by light limitation, but nitrogen, silicic acid as well as iron were all depleted to the extent that they could become co-limiting. This study illustrates the challenge associated with identification of the limiting nutrient, as it varied between phytoplankton groups, depths and sites. &copy; CSIRO 2014.
Laczka, O., Labbate, M. & Doblin, M. 2014, 'Application of an ELISA-type amperometric assay to the detection of Vibrio species with screen-printed electrodes', ANALYTICAL METHODS, vol. 6, no. 7, pp. 2020-2023.
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Everett, J.D., Baird, M.E., Roughan, M., Suthers, I.M. & Doblin, M.A. 2014, 'Relative impact of seasonal and oceanographic drivers on surface chlorophyll a along a Western Boundary Current', Progress in Oceanography, vol. 120, pp. 340-351.
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Strengthening Western Boundary Currents (WBCs) advect warm, low nutrient waters into temperate latitudes, displacing more productive waters. WBCs also influence phytoplankton distribution and growth through current-induced upwelling, mesoscale eddy intrusion and seasonal changes in strength and poleward penetration. Here we examine dynamics of chlorophyll a (Chl. a) in the western Pacific Ocean, a region strongly influenced by the East Australian Current (EAC). We interpreted a spatial and temporal analysis of satellite-derived surface Chl. a, using a hydrodynamic model, a wind-reanalysis product and an altimetry-derived eddy-census. Our analysis revealed regions of persistently elevated surface Chl. a along the continental shelf and showed that different processes have a dominant effect in different locations. In the northern and central zones, upwelling events tend to regulate surface Chl. a patterns, with peaks in phytoplankton biomass corresponding to two known upwelling locations south of Cape Byron (28.5&deg;S) and Smoky Cape (31&deg;S). Within the central EAC separation zone, positive surface Chl. a anomalies occurred 65% of the time when both wind-stress (?w) and bottom-stress (?B) were upwelling-favourable, and only 17% of the time when both were downwelling-favourable. The interaction of wind and the EAC was a critical driver of surface Chl. a dynamics, with upwelling-favourable ?W resulting in a 70% increase in surface Chl. a at some locations, when compared to downwelling-favourable ?W. In the southern zone, surface Chl. a was driven by a strong seasonal cycle, with phytoplankton biomass increasing up to 152% annually each spring. The Stockton Bight region (32.25-33.25&deg;S) contained ?20% of the total shelf Chl. a on 27% of occasions due to its location downstream of upwelling locations, wide shelf area and reduced surface velocities. This region is analogous to productive fisheries regions in the Aghulus Current (Natal Bight) and Kuroshio Current (Enshu-nada S...
Raven, J.A. & Doblin, M.A. 2014, 'Active water transport in unicellular algae: Where, why, and how', Journal of Experimental Botany, vol. 65, no. 22, pp. 6279-6292.
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&copy; 2014 &copy; The Author 2014. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. The occurrence of active water transport (net transport against a free energy gradient) in photosynthetic organisms has been debated for several decades. Here, active water transport is considered in terms of its roles, where it is found, and the mechanisms by which it could occur. First there is a brief consideration of the possibility of active water transport into plant xylem in the generation of root pressure and the refilling of embolized xylem elements, and from an unsaturated atmosphere into terrestrial organisms living in habitats with limited availability of liquid water. There is then a more detailed consideration of volume and osmotic regulation in wall-less freshwater unicells, and the possiblity of generation of buoyancy in marine phytoplankton such as large-celled diatoms. Calculations show that active water transport is a plausible mechanism to assist cells in upwards vertical movements, requires less energy than synthesis of low-density organic solutes, and potentially on a par with excluding certain ions from the vacuole.
Henschke, N., Everett, J.D., Doblin, M.A., Pitt, K.A., Richardson, A.J. & Suthers, I.M. 2014, 'Demography and interannual variability of salp swarms (Thalia democratica)', Marine Biology, vol. 161, no. 1, pp. 149-163.
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Swarms of the pelagic tunicate, Thalia democratica, form during spring, but the causes of the large interannual variability in the magnitude of salp swarms are unclear. Changes in asexual reproduction (buds per chain) of T. democratica populations in the coastal waters of south-east Australia (32-35&deg;S) were observed in three austral springs (October 2008-2010). T. democratica abundance was significantly higher in 2008 (1,312 individuals m-3) than 2009 and 2010 (210 and 92 individuals m-3, respectively). There was a significant negative relationship (linear regression, r 2 = 0.61, F 1,22 = 33.83, P < 0.001) between abundance and asexual reproduction. Similarly, relative growth rates declined with decreasing abundance. Generalised additive mixed modelling showed that T. democratica abundance was significantly positively related to preferred food >2 ?m in size (P < 0.05) and negatively related to the proportion of non-salp zooplankton (P < 0.001). Salp swarm magnitude, growth, and asexual reproduction may depend on the abundance of larger phytoplankton (prymnesiophytes and diatoms) and competition with other zooplankton. &copy; 2013 Springer-Verlag Berlin Heidelberg.
Laczka, O.F., Labbate, M., Seymour, J.R., Bourne, D.G., Fielder, S.S. & Doblin, M.A. 2014, 'Surface immuno-functionalisation for the capture and detection of vibrio species in the marine environment: A new management tool for industrial facilities', PLoS ONE, vol. 9, no. 10.
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&copy; 2014 Laczka et al. Bacteria from the genus Vibrio are a common and environmentally important group of bacteria within coastal environments and include species pathogenic to aquaculture organisms. Their distribution and abundance are linked to specific environmental parameters, including temperature, salinity and nutrient enrichment. Accurate and efficient detection of Vibrios in environmental samples provides a potential important indicator of overall ecosystem health while also allowing rapid management responses for species pathogenic to humans or species implicated in disease of economically important aquacultured fish and invertebrates. In this study, we developed a surface immuno-functionalisation protocol, based on an avidin-biotin type covalent binding strategy, allowing specific sandwich-type detection of bacteria from the Vibrio genus. The assay was optimized on 12 diverse Vibrio strains, including species that have implications for aquaculture industries, reaching detection limits between 7103 to 3104 cells mL-1. Current techniques for the detection of total Vibrios rely on laborious or inefficient analyses resulting in delayed management decisions. This work represents a novel approach for a rapid, accurate, sensitive and robust tool for quantifying Vibrios directly in industrial systems and in the environment, thereby facilitating rapid management responses.
Robinson, C., Suggett, D.J., Cherukuru, N., Ralph, P.J. & Doblin, M.A. 2014, 'Performance of Fast Repetition Rate fluorometry based estimates of primary productivity in coastal waters', Journal of Marine Systems, vol. 139, pp. 299-310.
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&copy; 2014 Published by Elsevier B.V. Capturing the variability of primary productivity in highly dynamic coastal ecosystems remains a major challenge to marine scientists. To test the suitability of Fast Repetition Rate fluorometry (FRRf) for rapid assessment of primary productivity in estuarine and coastal locations, we conducted a series of paired analyses estimating 14C carbon fixation and primary productivity from electron transport rates with a Fast Repetition Rate fluorometer MkII, from waters on the Australian east coast. Samples were collected from two locations with contrasting optical properties and we compared the relative magnitude of photosynthetic traits, such as the maximum rate of photosynthesis (Pmax), light utilisation efficiency (?) and minimum saturating irradiance (EK) estimated using both methods. In the case of FRRf, we applied recent algorithm developments that enabled electron transport rates to be determined free from the need for assumed constants, as in most previous studies. Differences in the concentration and relative proportion of optically active substances at the two locations were evident in the contrasting attenuation of PAR (400-700nm), blue (431nm), green (531nm) and red (669nm) wavelengths. FRRF-derived estimates of photosynthetic parameters were positively correlated with independent estimates of 14C carbon fixation (Pmax: n=19, R2=0.66; ?: n=21, R2=0.77; EK: n=19, R2=0.45; all p<0.05), however primary productivity was frequently underestimated by the FRRf method. Up to 81% of the variation in the relationship between FRRf and 14C estimates was explained by the presence of pico-cyanobacteria and chlorophyll-a biomass, and the proportion of photoprotective pigments, that appeared to be linked to turbidity. We discuss the potential importance of cyanobacteria in influencing the underestimations of FRRf productivity and steps to overcome this potential limitation.
Hong, Y., Burford, M.A., Ralph, P.J. & Doblin, M.A. 2014, 'Subtropical zooplankton assemblage promotes the harmful cyanobacterium Cylindrospermopsis raciborskii in a mesocosm experiment', Journal of Plankton Research, vol. 37, no. 1, pp. 90-101.
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&copy; The Author 2014. Harmful algal blooms (HABs) with public health impacts threaten freshwater ecosystems, including drinking water reservoirs, globally. Subtropical systems are often dominated by filamentous and colonial cyanobacteria, algae that are potentially less accessible for consumption by resident meso-zooplankton grazers. Less understood than selective grazing is the role of zooplankton in regenerating nutrients and facilitating growth of algae with efficient uptake strategies, such as the toxin-producing cyanobacterium, Cylindrospermopsis raciborskii. Using ?800-L bags suspended in the upper 3 m of the water column, we examined the growth of C. raciborskii under four treatments: 3 ambient zooplankton biomass, 10 zooplankton, 10 zooplankton plus inorganic P addition and a no amendment control (3Z, 10Z, 10ZP, control, respectively). After 4 days, C. raciborskii relative abundance doubled in the 10Z and 10ZP treatments compared with the control and 3Z treatments, and after 7 days P addition resulted in ?20% higher relative C. raciborskii biomass compared with other treatments, and an order of magnitude increase in N-fixing phytoplankton. The particulate C: P ratio declined in the 10Z and 10ZP mesocosms, indicating that meso-zooplankton facilitated P transfer to algae. Overall, the copepod dominated subtropical meso-zooplankton assemblage promoted C. raciborskii abundance and biomass over the short-term, demonstrating their facilitation of subtropical freshwater HAB formation.
Sackett, O., Armand, L., Beardall, J., Hill, R., Doblin, M., Connelly, C., Howes, J., Stuart, B., Ralph, P. & Heraud, P. 2014, 'Taxon-specific responses of Southern Ocean diatoms to Fe enrichment revealed by synchrotron radiation FTIR microspectroscopy', Biogeosciences Discussions, vol. 11, no. 5, pp. 7327-7357.
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Thompson, P.A., Bonham, P., Thomson, P., Rochester, W., Doblin, M.A., Waite, A.M., Richardson, A. & Rousseaux, C.S. 2014, 'Climate variability drives plankton community composition changes: The 2010-2011 El Niño to la Niña transition around Australia', Journal of Plankton Research, vol. 37, no. 5, pp. 966-984.
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&copy; 2015 The Author. The strong La Ni&ntilde;a of 2010-2011 provided an opportunity to investigate the ecological impacts of El Ni&ntilde;o-Southern Oscillation on coastal plankton communities using the nine national reference stations around Australia. Based on remote sensing and across the entire Australian region 2011 (La Ni&ntilde;a) was only modestly different from 2010 (El Ni&ntilde;o) with the average temperature declining 0.2%, surface chlorophyll a up 3% and modelled primary production down 14%. Other changes included a poleward shift in Prochlorococcus and Synechococcus. Along the east coast, there was a reduction in salinity, increase in nutrients, Chlorophytes and Prasinophytes (taxa with chlorophyll b, neoxanthin and prasinoxanthin). The southwest region had a rise in the proportion of 19-hexoyloxyfucoxanthin; possibly coccolithophorids in eddies of the Leeuwin Current and along the sub-tropical front. Pennate diatoms increased, Ceratium spp. decreased and Scrippsiella spp. increased in 2011. Zooplankton biomass declined significantly in 2011. There was a reduction in the abundance of Calocalanus pavo and Temora turbinata and increases in Clausocalanus farrani, Oncaea scottodicarloi and Macrosetella gracilis in 2011. The changes in the plankton community during the strong La Ni&ntilde;a of 2011 suggest that this climatic oscillation exacerbates the tropicalization of Australia.
Sinutok, S., Hill, R., Doblin, M.A. & Ralph, P.J. 2013, 'Diurnal photosynthetic response of the motile symbiotic benthic foraminiferan marginopora vertebralis', Marine Ecology Progress Series, vol. 478, pp. 127-138.
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Movement of the symbiont-bearing foraminiferan Marginopora vertebralis and photo physiological response to diurnal fluctuations in irradiance were investigated in field and laboratory experiments. The abundance of M. vertebralis from both light-exposed and sheltered habitats was determined 5 times during the day, from pre-dawn to post-dusk. M. vertebralis abundance was significantly higher in sheltered compared to exposed habitats at midday under high irradiance, and this movement enabled the algal symbionts to avoid excessive photoinhibition. The diurnal changes in photosynthetic efficiency were not consistent with the typical midday solar maximum downregulation of photosystem II observed in other photoautotrophs and was likely due to the negatively phototactic capacity of the foraminifera. To confirm the light-dependent movement of foraminifera, individuals in exposed and sheltered habitats were exposed to the photosynthetic inhibitor 3-(3,4-dichlorophenyl)-1, 1-dimethylurea (DCMU) in the laboratory. The lack of movement in DCMU-exposed specimens confirmed light-dependent movement and subsequent disruption of signalling between the host foraminiferan and the algal symbionts. Analysis of chlorophyll and xanthophyll pigments, as well as symbiont density, indicated that under high irradiance, foraminiferal symbionts have the capacity to reduce light stress by activating photoprotective mechanisms. The negatively phototactic behaviour prevented chlorophyll degradation, symbiont loss and bleaching, suggesting that it is the primary mechanism for controlling light exposure in these foraminifera. This behaviour provides a competitive advantage over other sessile organisms in avoiding photoinhibition and bleaching by moving away from over-saturating irradiance, towards less damaging light fields. &copy; Inter-Research 2013.
Clark, J.S., Poore, A.G.B., Ralph, P.J. & Doblin, M.A. 2013, 'Potential for adaptation in response to thermal stress in an intertidal macroalga', Journal of Phycology, vol. 49, no. 4, pp. 630-639.
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Understanding responses of marine algae to changing ocean temperatures requires knowledge of the impacts of elevated temperatures and the likelihood of adaptation to thermal stress. The potential for rapid evolution of thermal tolerance is dependent on the levels of heritable genetic variation in response to thermal stress within a population. Here, we use a quantitative genetic breeding design to establish whether there is a heritable variation in thermal sensitivity in two populations of a habitat-forming intertidal macroalga, Hormosira banksii (Turner) Descaisne. Gametes from multiple parents were mixed and growth and photosynthetic performance were measured in the resulting embryos, which were incubated under control and elevated temperature (20&deg;C and 28&deg;C). Embryo growth was reduced at 28&deg;C, but significant interactions between male genotype and temperature in one population indicated the presence of genetic variation in thermal sensitivity. Selection for more tolerant genotypes thus has the ability to result in the evolution of increased thermal tolerance. Furthermore, genetic correlations between embryos grown in the two temperatures were positive, indicating that those genotypes that performed well in elevated temperature also performed well in control temperature. Chlorophyll a fluorescence measurements showed a marked decrease in maximum quantum yield of photosystem II (PSII) under elevated temperature. There was an increase in the proportion of energy directed to photoinhibition (nonregulated nonphotochemical quenching) and a concomitant decrease in energy used to drive photochemistry and xanthophyll cycling (regulated nonphotochemical quenching). However, PSII performance between genotypes was similar, suggesting that thermal sensitivity is related to processes other than photosynthesis. &copy; 2013 Phycological Society of America.
Gobler, C.J., Lobanov, A.V., Tang, Y.Z., Turanov, A.A., Zhang, Y., Doblin, M., Taylor, G.T., Sañudo-Wilhelmy, S.A., Grigoriev, I.V. & Gladyshev, V.N. 2013, 'The central role of selenium in the biochemistry and ecology of the harmful pelagophyte, Aureococcus anophagefferens', ISME Journal, vol. 7, no. 7, pp. 1333-1343.
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The trace element selenium (Se) is required for the biosynthesis of selenocysteine (Sec), the 21st amino acid in the genetic code, but its role in the ecology of harmful algal blooms (HABs) is unknown. Here, we examined the role of Se in the biology and ecology of the harmful pelagophyte, Aureococcus anophagefferens, through cell culture, genomic analyses, and ecosystem studies. This organism has the largest and the most diverse selenoproteome identified to date that consists of at least 59 selenoproteins, including known eukaryotic selenoproteins, selenoproteins previously only detected in bacteria, and novel selenoproteins. The A. anophagefferens selenoproteome was dominated by the thioredoxin fold proteins and oxidoreductase functions were assigned to the majority of detected selenoproteins. Insertion of Sec in these proteins was supported by a unique Sec insertion sequence. Se was required for the growth of A. anophagefferens as cultures grew maximally at nanomolar Se concentrations. In a coastal ecosystem, dissolved Se concentrations were elevated before and after A. anophagefferens blooms, but were reduced by >95% during the peak of blooms to 0.05 nM. Consistent with this pattern, enrichment of seawater with selenite before and after a bloom did not affect the growth of A. anophagefferens, but enrichment during the peak of the bloom significantly increased population growth rates. These findings demonstrate that Se inventories, which can be anthropogenically enriched, can support proliferation of HABs, such as A. anophagefferens through its synthesis of a large arsenal of Se-dependent oxidoreductases that fine-tune cellular redox homeostasis. &copy; 2013 International Society for Microbial Ecology All rights reserved.
Hong, Y., Burford, M.A., Ralph, P.J., Udy, J.W. & Doblin, M.A. 2013, 'The cyanobacterium cylindrospermopsis raciborskii is facilitated by copepod selective grazing', Harmful Algae, vol. 29, pp. 14-21.
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Blooms of the toxin-producing cyanobacterium Cylindrospermopsis raciborskii occur in tropical and subtropical lakes during spring-summer but the mechanisms behind bloom formation are unclear. This study tests the hypothesis that C. raciborskii accumulations in freshwater systems are facilitated by selective copepod grazing. Prey selection was examined in a series of experiments with C. raciborskii and the green alga, Chlamydomonas reinhardtii, as well as within natural phytoplankton assemblages. Clearance rates of the copepod Boeckella sp. on a C. raciborskii diet were 2-4 times lower than that of a common cladoceran Ceriodaphnia sp. when both grazers had prey choice. More C. raciborskii was cleared by Boeckella sp. when in mixed natural phytoplankton assemblages, but the clearance rate declined when nutrient replete C. reinhardtii was added, demonstrating that when alternate "high quality" algae were present, so did C. raciborskii consumption. The clearance rates of Boeckella sp. on two toxic C. raciborskii strains were significantly lower than on a non-toxic strain, and on C. raciborskii with low cellular P content. When we tested the grazing preference of a copepod dominated mixed zooplankton community on C. raciborskii during the early bloom period, clearance rates were relatively low (0.05-0.20mlindividual-1h-1), and decreased significantly as the proportion of C. raciborskii increased above 5%. These results suggest that C. raciborskii persistence could be promoted by copepods preferentially grazing on other algae, with significant loss of top-down control as C. raciborskii abundance increases. &copy; 2013 Elsevier B.V.
Dafforn, K.A., Kelaher, B.P., Simpson, S.L., Coleman, M.A., Hutchings, P.A., Clark, G.F., Knott, N.A., Doblin, M.A. & Johnston, E.L. 2013, 'Polychaete Richness and Abundance Enhanced in Anthropogenically Modified Estuaries Despite High Concentrations of Toxic Contaminants', PLoS ONE, vol. 8, no. 9.
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Ecological communities are increasingly exposed to multiple chemical and physical stressors, but distinguishing anthropogenic impacts from other environmental drivers remains challenging. Rarely are multiple stressors investigated in replicated studies over large spatial scales (>1000 kms) or supported with manipulations that are necessary to interpret ecological patterns. We measured the composition of sediment infaunal communities in relation to anthropogenic and natural stressors at multiple sites within seven estuaries. We observed increases in the richness and abundance of polychaete worms in heavily modified estuaries with severe metal contamination, but no changes in the diversity or abundance of other taxa. Estuaries in which toxic contaminants were elevated also showed evidence of organic enrichment. We hypothesised that the observed response of polychaetes was not a 'positive' response to toxic contamination or a reduction in biotic competition, but due to high levels of nutrients in heavily modified estuaries driving productivity in the water column and enriching the sediment over large spatial scales. We deployed defaunated field-collected sediments from the surveyed estuaries in a small scale experiment, but observed no effects of sediment characteristics (toxic or enriching). Furthermore, invertebrate recruitment instead reflected the low diversity and abundance observed during field surveys of this relatively 'pristine' estuary. This suggests that differences observed in the survey are not a direct consequence of sediment characteristics (even severe metal contamination) but are related to parameters that covary with estuary modification such as enhanced productivity from nutrient inputs and the diversity of the local species pool. This has implications for the interpretation of diversity measures in large-scale monitoring studies in which the observed patterns may be strongly influenced by many factors that covary with anthropogenic modification. ...
Sackett, O., Petrou, K., Reedy, B., De Grazia, A., Hill, R., Doblin, M., Beardall, J., Ralph, P. & Heraud, P. 2013, 'Phenotypic plasticity of southern ocean diatoms: Key to success in the sea ice habitat?', PLoS ONE, vol. 8, no. 11.
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Diatoms are the primary source of nutrition and energy for the Southern Ocean ecosystem. Microalgae, including diatoms, synthesise biological macromolecules such as lipids, proteins and carbohydrates for growth, reproduction and acclimation to prevailing environmental conditions. Here we show that three key species of Southern Ocean diatom (Fragilariopsis cylindrus, Chaetoceros simplex and Pseudo-nitzschia subcurvata) exhibited phenotypic plasticity in response to salinity and temperature regimes experienced during the seasonal formation and decay of sea ice. The degree of phenotypic plasticity, in terms of changes in macromolecular composition, was highly species-specific and consistent with each species' known distribution and abundance throughout sea ice, meltwater and pelagic habitats, suggesting that phenotypic plasticity may have been selected for by the extreme variability of the polar marine environment. We argue that changes in diatom macromolecular composition and shifts in species dominance in response to a changing climate have the potential to alter nutrient and energy fluxes throughout the Southern Ocean ecosystem. &copy; 2013 Sackett et al.
Petrou, K., Kranz, S.A., Doblin, M.A. & Ralph, P.J. 2012, 'Photophysiological responses of fragilariopsis cylindrus (bacillariophyceae) to nitrogen depletion at two temperatures', Journal of Phycology, vol. 48, no. 1, pp. 127-136.
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The photosynthetic efficiency and photoprotective capacity of the sea-ice diatom, Fragilariopsis cylindrus (Grunow) W. Krieg., grown in a matrix of nitrogen repletion and depletion at two different temperatures (-1&deg;C and +6&deg;C) was investigated. Temperature showed no significant effect on photosynthetic efficiency or photoprotection in F. cylindrus. Cultures under nitrogen depletion showed enhanced photoprotective capacity with an increase in nonphotochemical quenching (NPQ) when compared with nitrogen-replete cultures. This phenomenon was achieved at no apparent cost to the photosynthetic efficiency of PSII (F V/F M). Nitrogen depletion yielded a partially reduced electron transport chain in which maximum fluorescence (F M) could only be obtained by adding 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). reoxidation curves showed the presence of Q B nonreducing PSII centers under nitrogen depletion. Fast induction curves (FICs) and electron transport rates (ETRs) revealed slowing of the electrons transferred from the primary (Q A) to the secondary (Q B) quinone electron acceptors of PSII. The data presented show that nitrogen depletion in F. cylindrus leads to the formation of Q B nonreducing PSII centers within the photosystem. On a physiological level, the formation of Q B nonreducing PSII centers in F. cylindrus provides the cell with protection against photoinhibition by facilitating the rapid induction of NPQ. This strategy provides an important ecological advantage, especially during the Antarctic spring, maintaining photosynthetic efficiency under high light and nutrient-limiting conditions. &copy; 2011 Phycological Society of America.
Hallegraeff, G.M., Blackburn, S.I., Doblin, M.A. & Bolch, C.J.S. 2012, 'Global toxicology, ecophysiology and population relationships of the chainforming PST dinoflagellate Gymnodinium catenatum', Harmful Algae, vol. 14, pp. 130-143.
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Increasing scientific awareness since the 1980s of the chain-forming dinoflagellate Gymnodinium catenatum has led to this species being reported with increased frequency in a globally increasing number of countries (23 at present). G. catenatum exhibits little molecular genetic variation in rDNA over its global range, in contrast to RAPD fingerprinting which points to high genetic variation within regional populations even between estuaries 50. km apart. All Australian and New Zealand strains possess a thymine nucleotide (T-gene) near the start of the 5.8S rRNA whereas all other global populations examined to date possess cytosine-nucleotide (C-gene), except for southern Japan which harbours both C-gene and T-gene strains. Together with cyst and plankton evidence this strongly suggests that both Australian and New Zealand populations have derived from southern Japan. Global dinoflagellate populations and cultures exhibit an extraordinary variation in PST profiles (STX and 21 analogues), but consistent regional patterns are evident with regard to the production of C1,2; C3,4; B1,2; and neoSTX analogues. PST profiles of cyst-derived cultures are deemed unrepresentative. Distinct ecophysiological differences exist between tropical (21-32&deg;C) and warm-temperate ecotypes (12-18&deg;C), but these appear unrelated to ITS genotypes and PST toxin phenotypes. On current evidence, cyst germination appears to play a minimal role in the bloom dynamics of this species, while seasonal and inter-annual bloom variations result from the physical constraints (temperature and light) on the growth of the dinoflagellates in the water column. G. catenatum exhibits a capacity to utilize many forms of nitrogen. Its chain formation and strong motility allow it to undergo retrieval migrations to exploit light and nutrient resource gradients in both stratified and mixed environments. Subtle strain-level variations in micronutrient (Se, humics) requirements and interaction with associated bacteri...
Gilbert, J.A., Hill, R., Doblin, M.A. & Ralph, P.J. 2012, 'Microbial consortia increase thermal tolerance of corals', Marine Biology, vol. 159, no. 8, pp. 1763-1771.
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This study examined the response of a coral holobiont to thermal stress when the bacterial community was treated with antibiotics. Colonies of Pocillopora damicornis were exposed to broad and narrow-spectrum antibiotics targeting coral-associated ? and ?-Proteobacteria. Corals were gradually heated from the control temperature of 26 to 31 &deg;C, and measurements were made of host, zooxanthellar and microbial condition. Antibiotics artificially reduced the abundance and activity of bacteria, but had minimal effect on zooxanthellae photosynthetic efficiency or host tissue protein content. Heated corals without antibiotics showed significant declines in F V/F M, typical of thermal stress. However, heated corals treated with antibiotics showed severe tissue loss in addition to a decline in F V/F M. This study demonstrated that a disruption to the microbial consortium diminished the resilience of the holobiont. Corals exposed to antibiotics under control temperature did not bleach, suggesting that temperature may be an important factor influencing the activity, diversity and ecological function of the holobiont bacterial community. &copy; 2012 Springer-Verlag.
Sinutok, S., Hill, R., Doblin, M.A., Kühl, M. & Ralph, P.J. 2012, 'Microenvironmental changes support evidence of photosynthesis and calcification inhibition in Halimeda under ocean acidification and warming', Coral Reefs, vol. 31, no. 4, pp. 1201-1213.
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The effects of elevated CO2 and temperature on photosynthesis and calcification of two important calcifying reef algae (Halimedamacroloba and Halimeda cylindracea) were investigated with O2 microsensors and chlorophyll a fluorometry through a combination of two pCO2 (400 and 1,200 ?atm) and two temperature treatments (28 and 32 &deg;C) equivalent to the present and predicted conditions during the 2100 austral summer. Combined exposure to pCO2 and elevated temperature impaired calcification and photosynthesis in the two Halimeda species due to changes in the microenvironment around the algal segments and a reduction in physiological performance. There were no significant changes in controls over the 5-week experiment, but there was a 50-70 % decrease in photochemical efficiency (maximum quantum yield), a 70-80 % decrease in O2 production and a threefold reduction in calcification rate in the elevated CO2 and high temperature treatment. Calcification in these species is closely coupled with photosynthesis, such that a decrease in photosynthetic efficiency leads to a decrease in calcification. Although pH seems to be the main factor affecting Halimeda species, heat stress also has an impact on their photosystem II photochemical efficiency. There was a strong combined effect of elevated CO2 and temperature in both species, where exposure to elevated CO2 or temperature alone decreased photosynthesis and calcification, but exposure to both elevated CO2 and temperature caused a greater decline in photosynthesis and calcification than in each stress individually. Our study shows that ocean acidification and ocean warming are drivers of calcification and photosynthesis inhibition in Halimeda. Predicted climate change scenarios for 2100 would therefore severely affect the fitness of Halimeda, which can result in a strongly reduced production of carbonate sediments on coral reefs under such changed climate conditions. &copy; 2012 Springer-Verlag.
Seymour, J.R., Doblin, M.A., Jeffries, T.C., Brown, M.V., Newton, K., Ralph, P.J., Baird, M. & Mitchell, J.G. 2012, 'Contrasting microbial assemblages in adjacent water masses associated with the East Australian Current', Environmental Microbiology Reports, vol. 4, no. 5, pp. 548-555.
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Different oceanographic provinces host discrete microbial assemblages that are adapted to local physicochemical conditions. We sequenced and compared the metagenomes of two microbial communities inhabiting adjacent water masses in the Tasman Sea, where the recent strengthening of the East Australian Current (EAC) has altered the ecology of coastal environments. Despite the comparable latitude of the samples, significant phylogenetic differences were apparent, including shifts in the relative frequency of matches to Cyanobacteria, Crenarchaeota and Euryarchaeota. Fine-scale variability in the structure of SAR11, Prochlorococcus and Synechococcus populations, with more matches to 'warm-water' ecotypes observed in the EAC, indicates the EAC may drive an intrusion of tropical microbes into temperate regions of the Tasman Sea. Furthermore, significant shifts in the relative importance of 17 metabolic categories indicate that the EAC prokaryotic community has different physiological properties than surrounding waters. &copy; 2012 Society for Applied Microbiology and Blackwell Publishing Ltd.
Petrou, K., Doblin, M.A. & Ralph, P.J. 2011, 'Heterogeneity in the photoprotective capacity of three Antarctic diatoms during short-term changes in salinity and temperature', Marine Biology, vol. 158, no. 5, pp. 1029-1041.
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The Antarctic marine ecosystem changes seasonally, forming a temporal continuum of specialised niche habitats including open ocean, sea ice and meltwater environments. The ability for phytoplankton to acclimate rapidly to the changed conditions of these environments depends on the species' physiology and photosynthetic plasticity and may ultimately determine their long-term ecological niche adaptation. This study investigated the photophysiological plasticity and rapid acclimation response of three Antarctic diatoms-Fragilariopsis cylindrus, Pseudo-nitzschia subcurvata and Chaetoceros sp.-to a selected range of temperatures and salinities representative of the sea ice, meltwater and pelagic habitats in the Antarctic. Fragilariopsis cylindrus displayed physiological traits typical of adaptation to the sea ice environment. Equally, this species showed photosynthetic plasticity, acclimating to the range of environmental conditions, explaining the prevalence of this species in all Antarctic habitats. Pseudo-nitzschia subcurvata displayed a preference for the meltwater environment, but unlike F. cylindrus, photoprotective capacity was low and regulated via changes in PSII antenna size. Chaetoceros sp. had high plasticity in non-photochemical quenching, suggesting adaptation to variable light conditions experienced in the wind-mixed pelagic environment. While only capturing short-term responses, this study highlights the diversity in photoprotective capacity that exists amongst three dominant Antarctic diatom species and provides insight into links between ecological niche adaptation and species' distribution. &copy; 2011 Springer-Verlag.
Earp, A., Hanson, C.E., Ralph, P.J., Brando, V.E., Allen, S., Baird, M., Clementson, L., Daniel, P., Dekker, A.G., Fearns, P.R.C.S., Parslow, J., Strutton, P.G., Thompson, P.A., Underwood, M., Weeks, S. & Doblin, M.A. 2011, 'Review of fluorescent standards for calibration of in situ fluorometers: Recommendations applied in coastal and ocean observing programs', Optics Express, vol. 19, no. 27, pp. 26768-26782.
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Fluorometers are widely used in ecosystem observing to monitor fluorescence signals from organic compounds, as well as to infer geophysical parameters such as chlorophyll or CDOM concentration, but measurements are susceptible to variation caused by biofouling, instrument design, sensor drift, operating environment, and calibration rigor. To collect high quality data, such sensors need frequent checking and regular calibration. In this study, a wide variety of both liquid and solid fluorescent materials were trialed to assess their suitability as reference standards for performance assessment of in situ fluorometers. Criteria used to evaluate the standards included the spectral excitation/emission responses of the materials relative to fluorescence sensors and to targeted ocean properties, the linearity of the fluorometer's optical response with increasing concentration, stability and consistency, availability and ease of use, as well as cost. Findings are summarized as a series of recommended reference standards for sensors deployed on stationary and mobile platforms, to suit a variety of in situ coastal to ocean sensor configurations. Repeated determinations of chlorophyll scale factor using the recommended liquid standard, Fluorescein, achieved an accuracy of 2.5%. Repeated measurements with the recommended solid standard, Plexiglas Satinice&reg; plum 4H01 DC (polymethylmethacrylate), over an 18 day period varied from the mean value by 1.0% for chlorophyll sensors and 3.3% for CDOM sensors. &copy; 2011 Optical Society of America.
Petrou, K., Hill, R., Doblin, M.A., McMinn, A., Johnson, R., Wright, S.W. & Ralph, P.J. 2011, 'Photoprotection of sea-ice microalgal communities from the east antarctic pack ice', Journal of Phycology, vol. 47, no. 1, pp. 77-86.
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All photosynthetic organisms endeavor to balance energy supply with demand. For sea-ice diatoms, as with all marine photoautotrophs, light is the most important factor for determining growth and carbon-fixation rates. Light varies from extremely low to often relatively high irradiances within the sea-ice environment, meaning that sea-ice algae require moderate physiological plasticity that is necessary for rapid light acclimation and photoprotection. This study investigated photoprotective mechanisms employed by bottom Antarctic sea-ice algae in response to relatively high irradiances to understand how they acclimate to the environmental conditions presented during early spring, as the light climate begins to intensify and snow and sea-ice thinning commences. The sea-ice microalgae displayed high photosynthetic plasticity to increased irradiance, with a rapid decline in photochemical efficiency that was completely reversible when placed under low light. Similarly, the photoprotective xanthophyll pigment diatoxanthin (Dt) was immediately activated but reversed during recovery under low light. The xanthophyll inhibitor dithiothreitol (DTT) and state transition inhibitor sodium fluoride (NaF) were used in under-ice in situ incubations and revealed that nonphotochemical quenching (NPQ) via xanthophyll-cycle activation was the preferred method for light acclimation and photoprotection by bottom sea-ice algae. This study showed that bottom sea-ice algae from the east Antarctic possess a high level of plasticity in their light-acclimation capabilities and identified the xanthophyll cycle as a critical mechanism in photoprotection and the preferred means by which sea-ice diatoms regulate energy flow to PSII. &copy; 2011 Phycological Society of America.
Hassler, C.S., Djajadikarta, J.R., Doblin, M.A., Everett, J.D. & Thompson, P.A. 2011, 'Characterisation of water masses and phytoplankton nutrient limitation in the East Australian Current separation zone during spring 2008', Deep-Sea Research Part II: Topical Studies in Oceanography, vol. 58, no. 5, pp. 664-677.
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This study focuses on the comparison of oceanic and coastal cold-core eddies with inner-shelf and East Australian Current (EAC) waters at the time of the spring bloom (October 2008). The surface water was biologically characterised by the phytoplankton biomass, composition, photo-physiology, carbon fixation and by nutrient-enrichment experiments. Marked differences in phytoplankton biomass and composition were observed. Contrasted biomarker composition suggests that biomarkers could be used to track water masses in this area. Divinyl chlorophyll a, a biomarker for tropical Prochlorophytes, was found only in the EAC. Zeaxanthin a biomarker for Cyanophytes, was found only within the oceanic eddy and in the EAC, whereas chlorophyll b (Chlorophytes) was only present in the coastal eddy and at the front between the inner-shelf and EAC waters. This study showed that cold-core eddies can affect phytoplankton, biomass, biodiversity and productivity. Inside the oceanic eddy, greater phytoplankton biomass and a more complex phytoplankton community were observed relative to adjacent water masses (including the EAC). In fact, phytoplankton communities inside the oceanic eddy more closely resembled the community observed in the inner-shelf waters. At a light level close to half-saturation, phytoplankton carbon fixation (gCd -1) in the oceanic eddy was 13-times greater than at the frontal zone between the eddy and the EAC and 3-times greater than in the inner-shelf water. Nutrient-enrichment experiments demonstrated that nitrogen was the major macronutrient limiting phytoplankton growth in water masses associated with the oceanic eddy. Although the effective quantum yield values demonstrate healthy phytoplankton communities, the phytoplankton community bloomed and shifted in response to nitrogen enrichments inside the oceanic eddy and in the frontal zone between this eddy and the EAC. An effect of Si enrichment was only observed at the frontal zone between the eddy and the EAC...
Doblin, M.A., Petrou, K.L., Shelly, K., Westwood, K., van den Enden, R., Wright, S., Griffiths, B. & Ralph, P.J. 2011, 'Diel variation of chlorophyll-a fluorescence, phytoplankton pigments and productivity in the Sub-Antarctic and Polar Front Zones south of Tasmania, Australia', Deep-Sea Research Part II: Topical Studies in Oceanography, vol. 58, no. 21-22, pp. 2189-2199.
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Marine primary production is a fundamental measure of the ocean's capacity to convert carbon dioxide to particulate organic carbon for the marine foodweb, and as such is an essential variable used in ecosystem and biogeochemical models to assess trophic dynamics and carbon cycling. The Sub-Antarctic Zone (SAZ) is a major sink for atmospheric carbon and exhibits large gradients in ocean conditions on both temporal and spatial scales. In this dynamic system, an understanding of small-scale temporal changes is critical for modelling primary production at larger scales. Thus, we investigated diel effects on maximum quantum yield of PSII (FV/FM), photosynthetic pigment pools and primary productivity in the western (Diel 1) and eastern SAZ region (Diel 3) south of Tasmania, Australia, and compared this to a station at the polar front (Diel 2). Phytoplankton in the eastern SAZ had the greatest diel response, with cells showing decreased FV/FM and increased biosynthesis and transformation of xanthophyll and other photoprotective pigments during the day, but only in the surface waters (0 and 10m). Diel responses diminished by 30m. Cells in the western SAZ had similar responses across the depths sampled, increasing their FV/FM during the night and increasing their xanthophyll pigment content during the day. Phytoplankton at the polar front (Diel 2) showed intermediate diel-related variations in photophysiology, with xanthophyll conversion and increases in photoprotective pigments during the day but constant FV/FM. These diel changes at all sampling stations had little impact on carbon fixation rates, although cells sampled from the deep chlorophyll maximum at the polar front had significantly lower maximum carbon fixation and minimum saturating irradiance (Ek) compared to the other depths and stations. Considering the oceanographic context, cells at Diel 1 and 2 received less light and were more deeply mixed than cells at Diel 3, causing a dampening of the diel response. T...
Petrou, K., Hassler, C.S., Doblin, M.A., Shelly, K., Schoemann, V., van den Enden, R., Wright, S. & Ralph, P.J. 2011, 'Iron-limitation and high light stress on phytoplankton populations from the Australian Sub-Antarctic Zone (SAZ)', Deep-Sea Research Part II: Topical Studies in Oceanography, vol. 58, no. 21-22, pp. 2200-2211.
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The high nutrient low chlorophyll (HNLC) surface waters of the Southern Ocean are characterised by high concentrations of nitrate and phosphate, low concentrations of dissolved iron and deep vertical mixing. Future climate scenarios predict increased surface temperatures and ocean stratification in the region. These changes to vertical mixing will result in a slowdown of nutrient supply to surface waters and an increase in the integrated irradiance in the upper mixed layer. To investigate the influence of iron-limitation and high irradiance on phytoplankton growth and physiology, a 6-day shipboard incubation experiment was conducted during the Sub-Antarctic Zone Sensitivity to Environmental Change (SAZ Sense) voyage using phytoplankton populations from the upper mixed layer in the north-eastern SAZ region. Iron-limitation was induced with an organic siderophore and was compared with a 1nM iron-enriched incubation and an unamended treatment (under silicate replete conditions). As expected, iron enrichment led to dominance by large diatoms and enhanced photosynthetic performance, while the iron-limited community showed a decline in total chl a and photochemical efficiency. Under the added stress of high light, the iron-limited community was able to cope with the shift from in situ (<150?molphotonsm-2s-1) to incubation (mean=765?molphotonsm-2s-1) irradiance by increasing the proportion of photoprotective pigments and diverting excess light energy via energy-dependent quenching (qE). The responses to iron-limitation under high light showed that the phytoplankton community was able to acclimate to these conditions, but exhibited an overall decline in photosynthetic activity. Data presented here suggest the community shifts, in particular the decrease in diatoms, and the decline in photosynthetic performance of phytoplankton under low iron-high irradiance conditions has the potential to impact future ocean productivity and biogeochemical cycling. &copy; 2011 Elsevier Ltd.
Baird, M.E., Suthers, I.M., Griffin, D.A., Hollings, B., Pattiaratchi, C., Everett, J.D., Roughan, M., Oubelkheir, K. & Doblin, M. 2011, 'The effect of surface flooding on the physical-biogeochemical dynamics of a warm-core eddy off southeast Australia', Deep-Sea Research Part II: Topical Studies in Oceanography, vol. 58, no. 5, pp. 592-605.
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Warm-core eddies (WCEs) formed from the East Australian Current (EAC) play an important role in the heat, mass and biogeochemical budgets of the western Tasman Sea. The development and separation of an EAC WCE during July-December 2008 was observed using remotely sensed temperature, ocean colour and sea-level elevation, three Argo floats, a shipboard CTD, a shelf mooring array and a 15-day deployment of a Slocum glider. The eddy formed from an EAC meander during the first half of 2008 and in late August had a ~275m deep surface mixed layer. In the two months before separation in early December, fresher and warmer EAC water flooded the top of the eddy, submerging the winter mixed layer. The rate of vertical transport due to submergence was estimated to be between 1 and 6Sv, at the time accounting for a significant fraction of the mean southward flow of the EAC. The core of the eddy had a surface chlorophyll a concentration of <0.4mgm-3 throughout the observations. A 20-40m thick pycnocline formed at the interface of the flooding surface waters and the submerged layer. Chlorophyll a concentration in the pycnocline ranged from 0.5 to 2mgm-3, with depth-integrated concentration ranging between 25 and 75mgm-2. The development of a sub-surface maximum suggests that flooding increased light levels in the pycnocline. Elevated levels of coloured dissolved organic matter in the submerged layer correspond to oxygen depletion, suggesting respiration of organic matter. A comparison is made with observations from WCEs in 1978 and 1997 in which, unusually, surface flooding did not occur, but solar heating stratified the top 50m. In the two eddies with surface capping, surface chlorophyll a concentrations were an order of magnitude higher than the 2008 flooded eddy, but depth-integrated chlorophyll a was similar. These findings suggest that EAC WCEs with relatively shallow surface flooding contain more phytoplankton biomass than surface images would suggest, with the vertical po...
Sinutok, S., Hill, R., Doblin, M.A., Wuhrer, R. & Ralph, P.J. 2011, 'Warmer more acidic conditions cause decreased productivity and calcification in subtropical coral reef sediment-dwelling calcifiers', Limnology and Oceanography, vol. 56, no. 4, pp. 1200-1212.
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The effects of elevated CO 2 and temperature on photosynthesis and calcification in the calcifying algae Halimeda macroloba and Halimeda cylindracea and the symbiont-bearing benthic foraminifera Marginopora vertebralis were investigated through exposure to a combination of four temperatures (28&deg;C, 30&deg;C, 32&deg;C, and 34&deg;C) and four CO 2 levels (39, 61, 101, and 203 Pa; pH 8.1, 7.9, 7.7, and 7.4, respectively). Elevated CO 2 caused a profound decline in photosynthetic efficiency (F V: F M), calcification, and growth in all species. After five weeks at 34&deg;C under all CO 2 levels, all species died. Chlorophyll (Chl) a and b concentration in Halimeda spp. Significantly decreased in 203 Pa, 32&deg;C and 34&deg;C treatments, but Chl a and Chl c 2 concentration in M. vertebralis was not affected by temperature alone, with significant declines in the 61, 101, and 203 Pa treatments at 28&deg;C. Significant decreases in F V: F M in all species were found after 5 weeks of exposure to elevated CO 2 (203 Pa in all temperature treatments) and temperature (32&deg;C and 34&deg;C in all pH treatments). The rate of oxygen prod&deg;Ction declined at 61, 101, and 203 Pa in all temperature treatments for all species. The elevated CO 2 and temperature treatments greatly reduced calcification (growth and crystal size) in M. vertebralis and, to a lesser extent, in Halimeda spp. These findings indicate that 32&deg;C and 101 Pa CO 2, are the upper limits for survival of these species on Heron Island reef, and we conclude that these species will be highly vulnerable to the predicted future climate change scenarios of elevated temperature and ocean acidification. &copy; 2011, by the American Society of Limnology and Oceanography, Inc.
Thompson, P.A., Bonham, P., Waite, A.M., Clementson, L.A., Cherukuru, N., Hassler, C. & Doblin, M.A. 2011, 'Contrasting oceanographic conditions and phytoplankton communities on the east and west coasts of Australia', Deep-Sea Research Part II: Topical Studies in Oceanography, vol. 58, no. 5, pp. 645-663.
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The composition and dynamics of the phytoplankton communities and hydrographic factors that control them are described for eastern and western Australia with a focus on the Eastern Australian Current (EAC) and Leeuwin Current (LC) between 27.5&deg; and 34.5&deg;S latitude. A total of 1685 samples collected from 1996 to 2010 and analysed for pigments by high performance liquid chromatography (HPLC) showed the average TChla (monovinyl+divinyl chlorophyll a) concentration on the west coast to be 0.28&plusmn;0.16?gL-1 while it was 0.58&plusmn;1.4?gL-1 on the east coast. Both coasts showed significant decreases in the proportions of picoplankton and relatively more nanoplankton and microplankton with increasing latitude. On both coasts the phytoplankton biomass (by SeaWiFS) increased with the onset of winter. At higher latitudes (>27.5&deg;S) the southeast coast developed a spring bloom (September) when the mean monthly, surface chlorophyll a (chla) concentration (by SeaWiFS) was 48% greater than on the south west coast. In this southern region (27.5-34.5&deg;S) Synechococcus was the dominant taxon with 60% of the total biomass in the southeast (SE) and 43% in the southwest (SW). Both the SE and SW regions had similar proportions of haptophytes; ~14% of the phytoplankton community. The SW coast had relatively more pelagophytes, prasinophytes, cryptophytes, chlorophytes and less bacillariophytes and dinophytes. These differences in phytoplankton biomass and community composition reflect the differences in seasonality of the 2 major boundary currents, the influence this has on the vertical stability of the water column and the average availability of nutrients in the euphotic zone. Seasonal variation in mixed layer depth and upwelling on the west coast appears to be suppressed by the Leeuwin Current. The long-term depth averaged (0-100m) nitrate concentration on the west coast was only 14% of the average concentration on the east coast. Redfield ratios for NO3:SiO2:PO4 were 6.5:11.9:1 on the east co...
Petrou, K., Hill, R., Brown, C.M., Campbell, D.A., Doblin, M.A. & Ralph, P.J. 2010, 'Rapid photoprotection in sea-ice diatoms from the East Antarctic pack ice', Limnology and Oceanography, vol. 55, no. 3, pp. 1400-1407.
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Photoinhibition and D1 protein re-synthesis were investigated in bottom-dwelling sea-ice microalgal communities from the East Antarctic pack ice during early spring. Bottom-dwelling sea-ice microalgal communities were dominated by diatoms that exhibited rapid photoprotection when exposed to a range of different light levels (10 ?mol photons m-2 s -1, 50 ?mol photons m-2 s-1, 100 ?mol photons m-2 s-1, and 200 ?mol photons m-2 s-1). Photosynthetic capacity of photosystem II (PSII) dropped significantly over 3 h under 200 ?mol photons m-2 s-1, but largely recovered when placed in a low-light environment (10 ?mol photons m-2 s-1) for an additional 3 h. PSII repair rates increased with increasing irradiance, and the D1-protein pool remained steady even under high light (200 ?mol photons m-2 s-1). Sea-ice diatoms showed a low intrinsic susceptibility to photoinactivation of PSII across all the light treatments, and a strong and irradiance-dependent induction of nonphotochemical quenching, which did not depend upon chloroplast protein synthesis, was also seen. These highly plastic organisms, once thought to be adapted to shade, are in fact well equipped to withstand rapid and relatively large changes in light at low temperatures with minimal long-term effect on their photosynthetic machinery. &copy; 2010, by the American Society of Limnology and Oceanography, Inc.
Doblin, M.A., Murphy, K.R. & Ruiz, G.M. 2010, 'Thresholds for tracing ships' ballast water: An Australian case study', Marine Ecology Progress Series, vol. 408, pp. 19-32.
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To limit the spread of non-indigenous marine species, ships can be legally required to conduct ballast water exchange (BWE) prior to discharging ballast water. It has been proposed to verify BWE by measuring concentrations of coastal tracers in ballast tanks, which should track their removal. Using 3 Australian ports as case studies (Port Botany, Port Curtis and Port Phillip Bay), each representing a different BWE verification difficulty level, the spatial and temporal variability of chromophoric dissolved organic matter (CDOM) and 3 trace elements (manganese [Mn], barium [Ba] and phosphorus [P]), were measured to assess their utility as tracers of coastal (unexchanged) ballast water. CDOM fluorescence at ?ex/?em = 320/414 nm (C2*) and 370/494 nm (C3*) and Mn concentrations were significantly higher in ports than in the adjacent Tasman Sea, except near port entrances and at a few sites in Port Botany. Ba concentrations demonstrated the least power to discriminate coastal sources, but P easily discriminated water from mesotrophic Port Phillip Bay. In general, tracers showed greater variation between and within ports, rather than between seasons. Conservative BWE thresholds were calculated to be 1.6 quinine sulphate equivalents for C2*, 0.9 quinine sulphate equivalents for C3*, 1.4 ?g l-1 for Mn and 6.9 ?g l -1 for Ba. Overall, these thresholds would allow water sourced from eastern Australian ports to be identified as coastal at 92%, 69% and 74% of sites examined using C3*, Mn and Ba, respectively, requiring 71 &plusmn; 26%, 54 &plusmn; 40% and 59 &plusmn; 38% replacement with mid-ocean water to be within ocean baseline concentration ranges. &copy; Inter-Research 2010 www.int-res.com.
Fahnenstiel, G., Hong, Y., Millie, D., Doblin, M., Johengen, T. & Reid, D. 2009, 'Marine dinoflagellate cysts in the ballast tank sediments of ships entering the Laurentian Great Lakes', INTERNATIONAL ASSOCIATION OF THEORETICAL AND APPLIED LIMNOLOGY, VOL 30, PT. 7, PROCEEDINGS, vol. 30, pp. 1035-1038.
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Gribben, P.E., Wright, J.T., O'Connor, W.A., Doblin, M.A., Eyre, B. & Steinberg, P.D. 2009, 'Reduced performance of native infauna following recruitment to a habitat-forming invasive marine alga', Oecologia, vol. 158, no. 4, pp. 733-745.
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Despite well-documented negative impacts of invasive species on native biota, evidence for the facilitation of native organisms, particularly by habitat-forming invasive species, is increasing. However, most of these studies are conducted at the population or community level, and we know little about the individual fitness consequences of recruitment to habitat-forming invasive species and, consequently, whether recruitment to these habitats is adaptive. We determined the consequences of recruitment to the invasive green alga Caulerpa taxifolia on the native soft-sediment bivalve Anadara trapezia and nearby unvegetated sediment. Initially, we documented the growth and survivorship of A. trapezia following a natural recruitment event, to which recruitment to C. taxifolia was very high. After 12 months, few clams remained in either habitat, and those that remained showed little growth. Experimental manipulations of recruits demonstrated that all performance measures (survivorship, growth and condition) were significantly reduced in C. taxifolia sediments compared to unvegetated sediments. Exploration of potential mechanisms responsible for the reduced performance in C. taxifolia sediments showed that water flow and water column dissolved oxygen (DO) were significantly reduced under the canopy of C. taxifolia and that sediment anoxia was significantly higher and sediment sulphides greater in C. taxifolia sediments. However, phytoplankton abundance (an indicator of food supply) was significantly higher in C. taxifolia sediments than in unvegetated ones. Our results demonstrate that recruitment of native species to habitat-forming invasive species can reduce growth, condition and survivorship and that studies conducted at the community level may lead to erroneous conclusions about the impacts of invaders and should include studies on life-history traits, particularly juveniles. &copy; 2008 Springer-Verlag.
Thompson, P.A., Baird, M.E., Ingleton, T. & Doblin, M.A. 2009, 'Long-term changes in temperate Australian coastal waters: Implications for phytoplankton', Marine Ecology Progress Series, vol. 394, pp. 1-19.
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A ?60 yr physical and chemical data set from 4 coastal stations around Australia plus remotely sensed SeaWiFS and phytoplankton taxonomic data were used to evaluate the temporal and spatial variation in phytoplankton ecology. The most consistent trend observed at all stations was a long-term increase in surface salinity of ?0.003 &plusmn; 0.0008 psu yr-1. All stations showed positive trends in temperature, with the fastest surface warming (0.0202&deg;C yr-1 over 60 yr) in the western Tasman Sea. Long-term trends in warming and stratification were more evident in some months and were not well characterized by annual averages. There was no general pattern of increasing stratification (0 to 50 m); only some stations and a few months showed significant changes. Long-term trends in surface nitrate and phosphate concentrations were either not significant (3 instances) or positive (5 instances) and were up to 6.1 nM phosphate yr-1. A pronounced decline in silicate was evident at the 3 east coast stations, with concentrations falling by as much as 58 nM yr-1 over the last ?30 yr. The western Tasman Sea experienced a ?50% decline in the growth rate and biomass of the spring bloom from 1997 to 2007, while other sites showed significant temporal variability in chlorophyll a that was associated with the Southern Oscillation Index (SOI). Diatoms tended to dominate the microplankton, especially during periods of low stratification. In conclusion, the physical, chemical and biological properties of Australian temperate waters have changed considerably over the last 60 yr in response to variation in the SOI and the strengthening East Australian Current. &copy; Inter-Research 2009.
Demir, E., Coyne, K.J., Doblin, M.A., Handy, S.M. & Hutchins, D.A. 2008, 'Assessment of microzooplankton grazing on Heterosigma akashiwo using a species- specific approach combining quantitative real-time PCR (QPCR) and dilution methods', Microbial Ecology, vol. 55, no. 4, pp. 583-594.
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Delaware's Inland Bays (DIB) are subject to numerous mixed blooms of harmful raphidophytes each year, and Heterosigma akashiwo is one of the consistently occurring species. Often, Chattonella subsalsa, C. cf. verruculosa, and Fibrocapsa japonica co-occur with H. akashiwo, indicating a dynamic consortium of raphidophyte species. In this study, microzooplankton grazing pressure was assessed as a top-down control mechanism on H. akashiwo populations in mixed communities. Quantitative real-time polymerase chain reaction (QPCR) with species-specific primers and probes were used in conjunction with the dilution method to assess grazing pressure on H. akashiwo and other raphidophytes. As a comparison, we measured changes in chlorophyll a (chl a) to determine whole community growth and mortality caused by grazing. We detected grazing on H. akashiwo using QPCR in samples where chl a analyses indicated little or no grazing on the total phytoplankton community. Overall, specific microzooplankton grazing pressure on H. akashiwo ranged from 0.88 to 1.88 day-1 at various sites. Experiments conducted on larger sympatric raphidophytes (C. subsalsa, C. cf. verruculosa and F. japonica) demonstrated no significant microzooplankton grazing on these species. Grazing pressure on H. akashiwo may provide a competitive advantage to other raphidophytes such as Chattonella spp. that are too large to be consumed at high rates by microzooplankton and help to shape the dynamics of this harmful algal bloom consortium. Our results show that QPCR can be used in conjunction with the dilution method for evaluation of microzooplankton grazing pressure on specific phytoplankton species within a mixed community. &copy; 2007 Springer Science+Business Media, LLC.
Petrou, K., Doblin, M.A., Smith, R.A., Ralph, P.J., Shelly, K. & Beardall, J. 2008, 'State transitions and nonphotochemical quenching during a nutrient-induced fluorescence transient in phosphorus-starved Dunaliella tertiolecta', Journal of Phycology, vol. 44, no. 5, pp. 1204-1211.
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Assessments of nutrient-limitation in microalgae using chl a fluorescence have revealed that nitrogen and phosphorus depletion can be detected as a change in chl a fluorescence signal when nutrient-starved algae are resupplied with the limiting nutrient. This photokinetic phenomenon is known as a nutrient-induced fluorescence transient, or NIFT. Cultures of the unicellular marine chlorophyte Dunaliella tertiolecta Butcher were grown under phosphate starvation to investigate the photophysiological mechanism behind the NIFT response. A combination of low temperature (77 K) fluorescence, photosynthetic inhibitors, and nonphotochemical quenching analyses were used to determine that the NIFT response is associated with changes in energy distribution between PSI and PSII and light-stress-induced nonphotochemical quenching (NPQ). Previous studies point to state transitions as the likely mechanism behind the NIFT response; however, our results show that state transitions are not solely responsible for this phenomenon. This study shows that an interaction of at least two physiological processes is involved in the rapid quenching of chl a fluorescence observed in P-starved D. tertiolecta: (1) state transitions to provide the nutrient-deficient cell with metabolic energy for inorganic phosphate (P i)-uptake and (2) energy-dependent quenching to allow the nutrient-stressed cell to avoid photodamage from excess light energy during nutrient uptake. &copy; 2008 Phycological Society of America.
Glibert, P.M., Azanza, R., Burford, M., Furuya, K., Abal, E., Al-Azri, A., Al-Yamani, F., Andersen, P., Anderson, D.M., Beardall, J., Berg, G.M., Brand, L., Bronk, D., Brookes, J., Burkholder, J.M., Cembella, A., Cochlan, W.P., Collier, J.L., Collos, Y., Diaz, R., Doblin, M., Drennen, T., Dyhrman, S., Fukuyo, Y., Furnas, M., Galloway, J., Granéli, E., Ha, D.V., Hallegraeff, G., Harrison, J., Harrison, P.J., Heil, C.A., Heimann, K., Howarth, R., Jauzein, C., Kana, A.A., Kana, T.M., Kim, H., Kudela, R., Legrand, C., Mallin, M., Mulholland, M., Murray, S., O'Neil, J., Pitcher, G., Qi, Y., Rabalais, N., Raine, R., Seitzinger, S., Salomon, P.S., Solomon, C., Stoecker, D.K., Usup, G., Wilson, J., Yin, K., Zhou, M. & Zhu, M. 2008, 'Ocean urea fertilization for carbon credits poses high ecological risks', Marine Pollution Bulletin, vol. 56, no. 6, pp. 1049-1056.
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The proposed plan for enrichment of the Sulu Sea, Philippines, a region of rich marine biodiversity, with thousands of tonnes of urea in order to stimulate algal blooms and sequester carbon is flawed for multiple reasons. Urea is preferentially used as a nitrogen source by some cyanobacteria and dinoflagellates, many of which are neutrally or positively buoyant. Biological pumps to the deep sea are classically leaky, and the inefficient burial of new biomass makes the estimation of a net loss of carbon from the atmosphere questionable at best. The potential for growth of toxic dinoflagellates is also high, as many grow well on urea and some even increase their toxicity when grown on urea. Many toxic dinoflagellates form cysts which can settle to the sediment and germinate in subsequent years, forming new blooms even without further fertilization. If large-scale blooms do occur, it is likely that they will contribute to hypoxia in the bottom waters upon decomposition. Lastly, urea production requires fossil fuel usage, further limiting the potential for net carbon sequestration. The environmental and economic impacts are potentially great and need to be rigorously assessed. &copy; 2008 Elsevier Ltd. All rights reserved.
Demir, E., Coyne, K.J., Doblin, M.A., Handy, S.M. & Hutchins, D.A. 2008, 'Assessment of microzooplankton grazing on Heterosigma akashiwo using a species- specific approach combining quantitative real-time PCR (QPCR) and dilution methods (Microbial Ecology DOI: 10.1007/s00248-007-9263-9)', Microbial Ecology, vol. 55, no. 4, pp. 581-582.
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Drake, L.A., Doblin, M.A. & Dobbs, F.C. 2007, 'Potential microbial bioinvasions via ships' ballast water, sediment, and biofilm', Marine Pollution Bulletin, vol. 55, no. 7-9, pp. 333-341.
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A prominent vector of aquatic invasive species to coastal regions is the discharge of water, sediments, and biofilm from ships' ballast-water tanks. During eight years of studying ships arriving to the lower Chesapeake Bay, we developed an understanding of the mechanisms by which invasive microorganisms might arrive to the region via ships. Within a given ship, habitats included ballast water, unpumpable water and sediment (collectively known as residuals), and biofilms formed on internal surfaces of ballast-water tanks. We sampled 69 vessels arriving from foreign and domestic ports, largely from Western Europe, the Mediterranean region, and the US East and Gulf coasts. All habitats contained bacteria and viruses. By extrapolating the measured concentration of a microbial metric to the estimated volume of ballast water, biofilm, or residual sediment and water within an average vessel, we calculated the potential total number of microorganisms contained by each habitat, thus creating a hierarchy of risk of delivery. The estimated concentration of microorganisms was greatest in ballast water ? sediment and water residuals ? biofilms. From these results, it is clear microorganisms may be transported within ships in a variety of ways. Using temperature tolerance as a measure of survivability and the temperature difference between ballast-water samples and the water into which the ballast water was discharged, we estimated 56% of microorganisms could survive in the lower Bay. Extrapolated delivery and survival of microorganisms to the Port of Hampton Roads in lower Chesapeake Bay shows on the order of 1020 microorganisms (6.8 1019 viruses and 3.9 1018 bacteria cells) are discharged annually to the region. &copy; 2006 Elsevier Ltd. All rights reserved.
Ralph, P.J., Durako, M.J., Enríquez, S., Collier, C.J. & Doblin, M.A. 2007, 'Impact of light limitation on seagrasses', Journal of Experimental Marine Biology and Ecology, vol. 350, no. 1-2, pp. 176-193.
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Seagrass distribution is controlled by light availability, especially at the deepest edge of the meadow. Light attenuation due to both natural and anthropogenically-driven processes leads to reduced photosynthesis. Adaptation allows seagrasses to exist under these sub-optimal conditions. Understanding the minimum quantum requirements for growth (MQR) is revealed when light conditions are insufficient to maintain a positive carbon balance, leading to a decline in seagrass growth and distribution. Respiratory demands of photosynthetic and non-photosynthetic tissues strongly influence the carbon balance, as do resource allocations between above- and below-ground biomass. Seagrass light acclimation occurs on varying temporal scales, as well as across spatial scales, from the position along a single leaf blade to within the canopy and finally across the meadow. Leaf absorptance is regulated by factors such as pigment content, morphology and physical properties. Chlorophyll content and morphological characteristics of leaves such as leaf thickness change at the deepest edge. We present a series of conceptual models describing the factors driving the light climate and seagrass responses under current and future conditions, with special attention on the deepest edge of the meadow. Crown Copyright &copy; 2007.
Doblin, M.A., Coyne, K.J., Rinta-Kanto, J.M., Wilhelm, S.W. & Dobbs, F.C. 2007, 'Dynamics and short-term survival of toxic cyanobacteria species in ballast water from NOBOB vessels transiting the Great Lakes-implications for HAB invasions', Harmful Algae, vol. 6, no. 4, pp. 519-530.
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We measured the presence, viability and potential toxicity of cyanobacteria in ships' ballast tanks during three domestic voyages through the North American Great Lakes. Using molecular methods, the toxin-producing forms of Microcystis and Anabaena were monitored in ballast water after ships' ballast tanks were filled at their first port of call, and at subsequent ports as ships transited the Great Lakes. Microcystis was detected in ballast water at intermediate and final ports of call in all three experiments, but the presence of Anabaena was more variable, suggesting low abundance or patchy distribution in ballast tanks. Both species were detected in ballast water up to 11 days old. Detection of the microcystin synthetase gene, mcyE, in ballast tanks indicated entrained cells were capable of producing microcystin, and further analyses of RNA indicated the toxin was being expressed by Microcystis, even after 11 days in dark transit. These data demonstrate within-basin transport and delivery of planktonic harmful algal bloom (HAB) species to distant ports in the world's largest freshwater reservoir, with potential implications for drinking water quality. These implications are discussed with respect to management of microbial invasions and the fate of introduced phytoplankton in their receiving environment. &copy; 2007 Elsevier B.V. All rights reserved.
Wilhelm, S.W., Carberry, M.J., Eldridge, M.L., Poorvin, L., Saxton, M.A. & Doblin, M.A. 2006, 'Marine and freshwater cyanophages in a Laurentian Great Lake: Evidence from infectivity assays and molecular analyses of g20 genes', Applied and Environmental Microbiology, vol. 72, no. 7, pp. 4957-4963.
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While it is well established that viruses play an important role in the structure of marine microbial food webs, few studies have directly addressed their role in large lake systems. As part of an ongoing study of the microbial ecology of Lake Erie, we have examined the distribution and diversity of viruses in this system. One surprising result has been the pervasive distribution of cyanophages that infect the marine cyanobacterial isolate Synechococcus sp. strain WH7803. Viruses that lytically infect this cyanobacterium were identified throughout the western basin of Lake Erie, as well as in locations within the central and eastern basins. Analyses of the gene encoding the g20 viral capsid assembly protein (a conservative phylogenetic marker for the cyanophage) indicate that these viruses, as well as amplicons from natural populations and the ballast of commercial ships, are related to marine cyanophages but in some cases form a unique clade, leaving questions concerning the native hosts of these viruses. The results suggest that cyanophages may be as important in freshwater systems as they are known to be in marine systems. Copyright &copy; 2006, American Society for Microbiology. All Rights Reserved.
Doblin, M.A., Thompson, P.A., Revill, A.T., Butler, E.C.V., Blackburn, S.I. & Hallegraeff, G.M. 2006, 'Vertical migration of the toxic dinoflagellate Gymnodinium catenatum under different concentrations of nutrients and humic substances in culture', Harmful Algae, vol. 5, no. 6, pp. 665-677.
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Vertical migration behaviour by the chainforming dinoflagellate Gymnodinium catenatum Graham was investigated using vertically-stratified laboratory columns. Under surface nutrient-deplete conditions, with nutrients added only at depth, 100% of cells underwent vertical migration (VM), starting downwards migration 3 h before the end of the light period and beginning upwards migration 3 h before the start of the light period. Cells in nutrient-replete columns showed no VM, but they were more dispersed in the upper layer during the dark compared to the light period. When surface layers (S) were nitrate-deplete (-N) and enriched with humic substances (H) contained in Huon River water and bottom waters (B) were nutrient replete (R) (SH-NBR), the pattern of VM was altered-50% of cells underwent migration and 50% remained at the pycnocline. In columns with nitrate-replete and humic-enriched surface layers (SHRBR), most cells underwent VM, while 30% remained at the surface. Cells in SH-NBR columns showed increased N quotas and intra-cellular nitrate concentrations after 4 days, indicating nitrate uptake by G. catenatum in bottom layers. The concomitant increase in particulate organic nitrogen (PON) with the decrease in external nitrate concentrations in bottom layers provide convincing evidence that VM by G. catenatum facilitates nutrient retrieval at depth. However, addition of humic substances (a potential source of organic nitrogen) to surface layers did not ameliorate G. catenatum N depletion sufficiently to preclude the need for NO3 - uptake at depth. Furthermore, there was no detectable pattern of increasing carbon (C) quota during the day (photosynthate accumulation) or increasing N quota during the night (nitrate assimilation). Toxic dinoflagellate G. catenatum blooms are commonly associated with nitrate depletion in surface waters in south-east Tasmanian waters (Australia). Therefore, vertical migration, facilitating N uptake at depth, could play an important ro...
Doblin, M.A. & Dobbs, F.C. 2006, 'Setting a size-exclusion limit to remove toxic dinoflagellate cysts from ships' ballast water', Marine Pollution Bulletin, vol. 52, no. 3, pp. 259-263.
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Dinoflagellate cysts are well-recognized biological constituents of ships' ballast tanks. They are present in ballast water, sediments and residual water in drained tanks, and in biofilms formed on interior tank surfaces. Therefore, cysts have the potential to be released during ballast discharge. The International Maritime Organization's (IMO) Ballast Water Management Convention (promulgated February 2004) stipulates a performance standard (Annex, Regulation D2) requiring discharged ballast water contain <10 viable organisms between 10 and 50 ?m per ml and <10 viable organisms ?50 ?m per m 3. The proposed size limit has potential to exclude both the smallest toxic and the largest toxic and non-toxic dinoflagellate (and other microalgal) cysts from discharged ballast water. Despite the appropriateness of size cutoffs however, ballast water containing predominantly small cysts (<50 ?m) could be deemed in compliance with the performance standard, even without treatment, while ballast water having the same concentration of larger cysts (>50 ?m) could require a multiple-log reduction in abundance before its permissible discharge. Also of concern, it remains uncertain whether ballast-water treatment can remove sufficient organisms, including dinoflagellate cysts, to meet the performance standard. &copy; 2006 Elsevier Ltd. All rights reserved.
Doblin, M.A., Baines, S.B., Cutter, L.S. & Cutter, G.A. 2006, 'Sources and biogeochemical cycling of particulate selenium in the San Francisco Bay estuary', Estuarine, Coastal and Shelf Science, vol. 67, no. 4, pp. 681-694.
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As part of a study of estuarine selenium cycling, we measured the concentration, chemical form (speciation), and distribution of particulate selenium under various river flow conditions in the North San Francisco Bay (from the Golden Gate to the Sacramento and San Joaquin Rivers). We also conducted laboratory studies on the accumulation of selenium by phytoplankton, the critical first step in the transformation of dissolved to particulate selenium. Total particulate selenium concentration in the North SF Bay was relatively constant between high and low flow periods, ranging spatially from 0.05 to 0.35 nmol l-1 and comprising between 5 and 12% of the total water column selenium inventory. Mean concentrations were generally highest in the Carquinez Strait-Suisun Bay region (salinity 0-17) and lowest in Central Bay. However, selenium content of suspended particles varied with river flow, with higher content during low flow (9.76 &plusmn; 4.17 nmol g-1; mean &plusmn; sd; n = 67) compared to high flow (7.10 &plusmn; 4.24 nmol g-1; n = 39). Speciation analyses showed that most particulate selenium is organic selenide (45 &plusmn; 27%), with a smaller proportion (typically <30%) of adsorbed selenite + selenate and a varying proportion (35 &plusmn; 28%) of elemental selenium. Based on the amount of elemental selenium in the seston (total suspended material), we calculate that resuspension of estuarine sediments could contribute 29-100% of particulate selenium in the water column. While selenium content of SF Bay seston (>0.4 ?m) is relatively unenriched compared to phytoplankton (13.6-155 nmol g-1 dry weight) on a mass basis, when normalized to carbon or nitrogen, seston contains a similar selenium concentration to SF Bay sediments or phytoplankton cultures. SF Bay seston is thus comprised of selenium-rich phytoplankton and phyto-detritus, but also inorganic clay mineral particles that effectively "dilute" total particulate selenium. Selenium concentrations in algal cultures (11 species) exposed to 90 nmo...
Handy, S.M., Coyne, K.J., Portune, K.J., Demir, E., Doblin, M.A., Hare, C.E., Cary, S.C. & Hutchins, D.A. 2006, 'Erratum: Evaluating vertical migration behavior of harmful raphidophytes in the Delaware Inland Bays utilizing quantitative real-time PCR (Aquatic Microbial Ecology (2005) 40, (121-132))', Aquatic Microbial Ecology, vol. 42, no. 3, p. 311.
Coyne, K.J., Handy, S.M., Demir, E., Whereat, E.B., Hutchins, D.A., Portune, K.J., Doblin, M.A. & Cary, S.C. 2005, 'Improved quantitative real-time PCR assays for enumeration of harmful algal species in field samples using an exogenous DNA reference standard', Limnology and Oceanography: Methods, vol. 3, no. SEP., pp. 381-391.
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Quantitative real-time PCR (QPCR) is a powerful and sensitive method for quantitative detection of microorganisms. Application of this methodology for enumeration of harmful algal bloom (HAB) species has the potential to revolutionize our approach to HAB research, making it possible to identify correlations between cell abundances and factors that regulate bloom dynamics. Its application to ecological studies, however, has produced mixed results. QPCR assays typically rely on the generation of standard curves from plasmids or laboratory cultures that may be unrealistic when compared to amplification of DNA extracted from field samples. In addition, existing methods often fail to incorporate controls to assess variability in extraction and amplification efficiencies, or include controls that are sequence-specific and preclude the investigation of multiple species. Here, we describe the development and rigorous analysis of QPCR assays for two HAB species, Chattonella subsalsa and Heterosigma akashiwo, in which we introduce a known concentration of exogenous DNA plasmid into the extraction buffer as a reference standard. Since the target DNA is extracted in the presence of the reference standard, inherent variability in extraction and amplification efficiencies affect both target and standard equally. Furthermore, the reference standard is applicable to QPCR analysis of any microbial species. Using environmental bloom samples as calibrators, we evaluated the accuracy of the comparative Ct method for enumeration of target species in several field samples. Our investigation demonstrates that the comparative Ct method with an exogenous DNA reference standard provides both accurate and reproducible quantification of HAB species in environmental samples. &copy; 2005, by the American Society of Limnology and oceanography, Inc.
Handy, S.M., Coyne, K.J., Portune, K.J., Demir, E., Doblin, M.A., Hare, C.E., Cary, S.C. & Hutchins, D.A. 2005, 'Evaluating vertical migration behavior of harmful raphidophytes in the Delaware Inland Bays utilizing quantitative real-time PCR', Aquatic Microbial Ecology, vol. 40, no. 2, pp. 121-132.
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Mixed blooms of 4 species of harmful raphidophytes (Chattonella cf. verruculosa, Chattonella subsalsa, Heterosigma akashiwo, and Fibrocapsa japonica) occur in the shallow (1 to 2 m) Delaware Inland Bays (DIB), USA. Raphidophytes vertically migrate in other deeper water ecosystems to utilize deep nutrient stocks at night, and thus obtain an advantage over non-migrating algae. Anoxic DIB sediments release high levels of bioavailable phosphate, which could potentially be used by vertically migrating flagellates. This study aimed to characterize and understand the migration patterns of DIB raphidophytes, and determine whether benthic phosphate fluxes could provide the cells with P. We demonstrated vertical migration of isolated DIB raphidophyte cultures in the laboratory, where differences in the response of C. subsalsa and H. akashiwo to light:dark period manipulations suggested possible differences in external versus endogenous regulation of migration behavior in the 2 species. Natural blooms in the field (enclosed in a mesocosm system) also exhibited patterns of diel vertical migration, as determined by quantitative real-time PCR (QPCR) used to enumerate the diel vertical distributions of each species. Our data suggested that these 2 photoautotrophic species spend daylight hours near the surface and are found directly on the sediment surface at night. However, diel changes in particulate C:P ratios did not support the hypothesis that there is preferential uptake of sedimentary phosphate at night. Our results also suggested that the migration behavior may have important implications for designing sampling strategies for monitoring programs. QPCR has a number of decisive advantages over traditional microscopic counting methods, making this a powerful tool for fine spatial and temporal scale detection and enumeration of vertically migrating harmful algal species. &copy; Inter-Research 2005.
Drake, L.A., Meyer, A.E., Forsberg, R.L., Baier, R.E., Doblin, M.A., Heinemann, S., Johnson, W.P., Koch, M., Rublee, P.A. & Dobbs, F.C. 2005, 'Potential invasion of microorganisms and pathogens via 'interior hull fouling': Biofilms inside ballast water tanks', Biological Invasions, vol. 7, no. 6, pp. 969-982.
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Surfaces submerged in an aquatic milieu are covered to some degree with biofilms - organic matrices that can contain bacteria, microalgae, and protozoans, sometimes including disease-causing forms. One unquantified risk of aquatic biological invasions is the potential for biofilms within ships' ballast water tanks to harbor pathogens, and, in turn, seed other waters. To begin to evaluate this vector, we collected biofilm samples from tanks' surfaces and deployed controlled-surface sampling units within tanks. We then measured a variety of microbial metrics within the biofilms to test the hypotheses that pathogens are present in biofilms and that biofilms have higher microbial densities compared to ballast water. Field experiments and sampling of coastwise and oceangoing ships arriving at ports in Chesapeake Bay and the North American Great Lakes showed the presence of abundant microorganisms, including pathogens, in biofilms. These results suggest that ballast-tank biofilms represent an additional risk of microbial invasion, provided they release cells into the water or they are sloughed off during normal ballasting operations. &copy; Springer 2005.
Doblin, M.A., Popels, L.C., Coyne, K.J., Hutchins, D.A., Cary, S.C. & Dobbs, F.C. 2004, 'Transport of the harmful bloom alga Aureococcus anophagefferens by oceangoing ships and coastal boats', Applied and Environmental Microbiology, vol. 70, no. 11, pp. 6495-6500.
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It is well established that cyst-forming phytoplankton species are transported in ships' ballast tanks. However, there is increasing evidence that other phytoplankton species which do not encyst are also capable of surviving ballast transit. These species have alternative modes of nutrition (hetero- or mixotrophy) and/or are able to survive long-term darkness. In our studies of no-ballast-on-board vessels arriving in the Great Lakes, we tested for the presence of the harmful algal bloom species Aureococcus anophagefferens (brown tide) in residual (i.e., unpumpable) ballast water using methods based on the PCR. During 2001, the brown tide organism was detected in 7 of 18 ballast water tanks in commercial ships following transit from foreign ports. Furthermore, it was detected after 10 days of ballast tank confinement during a vessel transit in the Great Lakes, a significant result given the large disparity between the salinity tolerance for active growth of Aureococcus (>22 ppt) and the low salinity of the residual ballast water (?2 ppt). We also investigated the potential for smaller, recreational vessels to transport and distribute Aureococcus. During the summer of 2002, 11 trailered boats from the inland bays of Delaware and coastal bays of Maryland were sampled. Brown tide was detected in the bilge water in the bottoms of eight boats, as well as in one live-well sample. Commercial ships and small recreational boats are therefore implicated as potential vectors for long-distance transport and local-scale dispersal of Aureococcus.
Baines, S.B., Fisher, N.S., Doblin, M.A., Cutter, G.A., Cutter, L.S. & Cole, B. 2004, 'Light dependence of selenium uptake by phytoplankton and implications for predicting selenium incorporation into food webs', Limnology and Oceanography, vol. 49, no. 2, pp. 566-578.
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The potentially toxic element selenium is first concentrated from solution to a large but highly variable degree by algae and bacteria before being passed on to consumers. The large loads of abiotic and detrital suspended particles often present in rivers and estuaries may obscure spatial and temporal patterns in Se concentrations at the base of the food web. We used radiotracers to estimate uptake of both selenite (Se(IV)) and C by intact plankton communities at two sites in the Sacramento/San Joaquin River Delta. Our goals were to determine (1) whether C and Se(IV) uptake were coupled, (2) the role of bacteria in Se(IV) uptake, and (3) the Se:C uptake ratio of newly produced organic material. Se(IV) uptake, like C uptake, was strongly related to irradiance. The shapes of both relationships were very similar except that at least 42-56% of Se(IV) uptake occurred in the dark, whereas C uptake in the dark was negligible. Of this dark Se(IV) uptake, 34-67% occurred in the 0.2-1.0-?m size fraction, indicating significant uptake by bacteria. In addition to dark uptake, total Se(IV) uptake consisted of a light-driven component that was in fixed proportion to C uptake. Our estimates of daily areal Se(IV):C uptake ratios agreed very well with particulate Se:C measured at a site dominated by phytoplankton biomass. Estimates of bacterial Se:C were 2.4-13 times higher than for the phytoplankton, suggesting that bacteriovores may be exposed to higher dietary Se concentrations than herbivores.
Stewart, A.R., Luoma, S.N., Schlekat, C.E., Doblin, M.A. & Hieb, K.A. 2004, 'Food web pathway determines how selenium affects aquatic ecosystems: A San francisco Bay case study', Environmental Science and Technology, vol. 38, no. 17, pp. 4519-4526.
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Chemical contaminants disrupt ecosystems, but specific effects may be under-appreciated when poorly known processes such as uptake mechanisms, uptake via diet, food preferences, and food web dynamics are influential. Here we show that a combination of food web structure and the physiology of trace element accumulation explain why some species in San Francisco Bay are threatened by a relatively low level of selenium contamination and some are not. Bivalves and crustacean Zooplankton form the base of two dominant food webs in estuaries. The dominant bivalve Potamocorbula amurensis has a 10-fold slower rate constant of loss for selenium than do common crustaceans such as copepods and the mysid Neomysis mercedis (rate constant of loss, k e = 0.025, 0.155, and 0.25 d -1, respectively). The result is much higher selenium concentrations in the bivalve than in the crustaceans. Stable isotope analyses show that this difference is propagated up the respective food webs in San Francisco Bay. Several predators of bivalves have tissue concentrations of selenium that exceed thresholds thought to be associated with teratogenesis or reproductive failure (liver Se > 15 ?g g -1 dry weight). Deformities typical of selenium-induced teratogenesis were observed in one of these species. Concentrations of selenium in tissues of predators of Zooplankton are less than the thresholds. Basic physiological and ecological processes can drive wide differences in exposure and effects among species, but such processes are rarely considered in traditional evaluations of contaminant impacts.
Aridgides, L.J., Doblin, M.A., Berke, T., Dobbs, F.C., Matson, D.O. & Drake, L.A. 2004, 'Multiplex PCR allows simultaneous detection of pathogens in ships' ballast water', Marine Pollution Bulletin, vol. 48, no. 11-12, pp. 1096-1101.
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There is enormous potential for global transfer of microorganisms, including pathogens, in ships' ballast water. We contend that a major advancement in the study of ballast-water microorganisms in particular, and of aquatic pathogens in general, will be expedited sample analysis, such as provided by the elegant technology of DNA microarrays. In order to use DNA microarrays, however, one must establish the appropriate conditions to bind target sequences in samples to multiple probes on the microarrays. We conducted proof-of-concept experiments to optimize simultaneous detection of multiple microorganisms using polymerase chain reaction (PCR) and Southern hybridization. We chose three target organisms, all potentially found in ballast water: a calicivirus, the bacterium Vibrio cholerae, and the photosynthetic protist Aureococcus anophagefferens. Here, we show simultaneous detection of multiple pathogens is possible, a result supporting the promising future use of microarrays for simultaneous detection of pathogens in ballast water. &copy; 2003 Elsevier Ltd. All rights reserved.
Purkerson, D.G., Doblin, M.A., Bollens, S.M., Luoma, S.N. & Cutter, G.A. 2003, 'Selenium in San Francisco Bay zooplankton: Potential effects of hydrodynamics and food web interactions', Estuaries, vol. 26, no. 4, pp. 956-969.
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The potential toxicity of elevated selenium (Se) concentrations in aquatic ecosystems has stimulated efforts to measure Se concentrations in benthos, nekton, and waterfowl in San Francisco Bay (SF Bay). In September 1998, we initiated a 14 mo field study to determine the concentration of Se in SF Bay zooplankton, which play a major role in the Bay food web, but which have not previously been studied with respect to Se. Monthly vertical plankton tows were collected at several stations throughout SF Bay, and zooplankton were separated into two operationally defined size classes for Se analyses: 73-2,000 ?m, and ?2,000 ?m. Selenium values ranged 1.02-6.07 ?g Se g-1 dry weight. No spatial differences in zooplankton Se concentrations were found. However, there were inter- and intra-annual differences. Zooplankton Se concentrations were enriched in the North Bay in Fall 1999 when compared to other seasons and locations within and outside SF Bay. The abundance and biovolume of the zooplankton community varied spatially between stations, but not seasonally within each station. Smaller herbivorous-omnivorous zooplankton had higher Se concentrations than larger omnivorous-carnivorous zooplankton. Selenium concentrations in zooplankton were negatively correlated with the proportion of total copepod biovolume comprising the large carnivorous copepod Tortanus dextrilobatus, but positively correlatid with the proportion of copepod biovolume comprising smaller copepods of the family Oithonidae, suggesting an important role of trophic level and size in regulating zooplankton Se concentrations. &copy; 2003 Estuarine Research Federation.
Laroussi, M., Dobbs, F.C., Wei, Z., Doblin, M.A., Ball, L.G., Moreira, K.R., Dyer, F.F. & Richardson, J.P. 2002, 'Decontamination of water by excimer UV radiation', IEEE Transactions on Plasma Science, vol. 30, no. 4 I, pp. 1501-1503.
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Water is one of the most important substances on which life depends. However, water may also serve as a medium by which disease is spread to humans, animals, and plants. Therefore, the biological decontamination of this vital substance is of paramount importance. Several methods have been used to decontaminate water and assure its clean supply. Unfortunately, most of these methods use potentially hazardous chemicals, which require proper storage and transport and are not environmentally friendly. Here we present a decontamination method based on the use of UV radiation emitted by the decay of excimers generated by a nonequilibrium discharge operating in the high-pressure regime. We found that at an appropriate wavelength, this type of UV radiation has a devastating effect on micro-organisms.
Baines, S.B., Fisher, N.S., Doblin, M.A. & Cutter, G.A. 2001, 'Uptake of dissolved organic selenides by marine phytoplankton', Limnology and Oceanography, vol. 46, no. 8, pp. 1936-1944.
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Se is present in multiple oxidation states in nature, each of which has unique chemical and biological reactivities. As a consequence, the rate of Se incorporation into food webs or its role as either a limiting nutrient or a toxic substance is a function of complex biogeochemistry. In particular, little is understood about the accumulation of dissolved organic selenides by phyto- or bacterioplankton. We assessed the bioavailability of dissolved organic selenides to marine and estuarine phytoplankton by presenting various algal species with filtered lysates of the diatom, Thalassiosira pseudonana, grown on media amended with radiolabeled selenite (75Se[IV]). Species known to accumulate selenite effectively also accumulated Se from radiolabeled cell lysates and to approximately the same extent. When exposed to a 4.5-nM solution of lysate Se, T. pseudonana, Heterocapsa triquetra (Dinophyceae), Tetraselmis levis (Prasinophyceae), Synechococcus bacillus (Cyanobacteria), and Dunaliella tertiolecta (Chlorophyceae) incorporated 42%-53%, 42%, 30%, 32%, and 4% of the dissolved Se, respectively. Se cell contents of T. pseudonana, T. levis, and D. tertiolecta grown in media containing 4.5 nM lysate Se were very similar to Se content of cells grown in 4.5 nM selenite. Our results suggest that recycling of Se(-II) may be more important than previously thought. Consequently, uptake of organic selenides by phytoplankton may need to be considered in models predicting Se incorporation into aquatic food webs, given that it is a significant fraction of dissolved Se in estuarine and oceanic waters.
Doblin, M.A., Blackburn, S.I. & Hallegraeff, G.M. 2000, 'Intraspecific variation in the selenium requirement of different geographic strains of the toxic dinoflagellate Gymnodinium catenatum', Journal of Plankton Research, vol. 22, no. 3, pp. 421-432.
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The requirement for selenium (iv) was assessed in five strains of the toxic dinoflagellate Gymnodinium catenatum Graham, representing three populations from Tasmania (australia), as well as one each from Japan and Spain. Strains were grown in nutrient-enriched sea water medium with 10-9 M selenium added as selenite (H2SeO3), or with no added selenium, and monitored for growth and cell yield. Strains exhibited different selenium (se) requirements, as evidenced by (i) a decrease in exponential growth rate (10-20%) and cell yield (up to 80%) (Japanese strain); (ii) a decrease in cell yield only (Tasmania Derwent Estuary 1987, Tasmania Huon Estuary and Spanish strains); and (iii) no decrease in growth or cell yield (tasmania Derwent Estuary 1993 strain). Variation in the response to Se deficiency was greatest between the two strains isolated from the Derwent Estuary, Tasmania, in different years (1987 and 1993) and less between Tasmanian strains from different localities (huon and Derwent Estuaries are 50 km apart) or between Tasmanian and Japanese or Spanish strains. Strain variability in micro-nutrient responses such as described here may provide a partial explanation for different bloom patterns exhibited by the same dinoflagellate taxon under apparently similar environmental conditions.
Doblin, M.A., Blackburn, S.I. & Hallegraeff, G.M. 1999, 'Comparative study of selenium requirements of three phytoplankton species: Gymnodinium catenatum, Alexandrium minutum (Dinophyta) and Chaetoceros cf. tenuissimus (Bacillariophyta)', Journal of Plankton Research, vol. 21, no. 6, pp. 1153-1169.
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This study investigated the selenium (Se) requirements of three phytoplankton species which commonly bloom in southern Australian estuaries. The present study showed that the toxic dinoflagellate Gymnodinium catenatum Graham had an obligate requirement for Se (IV) in culture. After two transfers (~4 weeks ? 7 generations) in Se-deficient seawater medium, this phytoplankton species exhibited a decline in growth rate (25%) and biomass yield (90%), while complete cessation of cell division occurred under prolonged (8 weeks ? 12 generations) Se starvation. Addition of 10-9-10-7 M H2SeO3 to nutrient-enriched seawater medium resulted in increased G.catenatum growth and biomass yields in direct proportion to the Se concentrations offered. In contrast to G.catenatum, Se limitation was observed in the dinoflagellate Alexandrium minutum Halim after four transfers (5 weeks ? 20 generations) in Se-deficient medium. Exponential growth rates of A.minutum decreased slightly (5-10%) when Se was not supplied, but biomass yields decreased as much as 80-90%. The diatom Chaetoceros cf. tenuissimus Meunier showed no evidence of Se limitation even after eight transfers (8 weeks; >60 generations) in Se-deficient medium. Variations in growth rates and biomass yields between transfers provide valuable information about the relative potential for Se limitation in the three species studied. In addition, differences in Se requirement between these bloom-forming phytoplankton species suggest that this micronutrient may play a role in structuring phytoplankton communities in southern Australian waters.
Doblin, M.A., Blackburn, S.I. & Hallegraeff, G.M. 1999, 'Growth and biomass stimulation of the toxic dinoflagellate Gymnodinium catenatum (Graham) by dissolved organic substances', Journal of Experimental Marine Biology and Ecology, vol. 236, no. 1, pp. 33-47.
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Blooms of the toxic dinoflagellate Gymnodinium catenatum are annually recurrent events in south-east Tasmanian waters. Extensive blooms are preceded by a rainfall 'trigger' and the associated influx of dissolved organic matter (DOM; otherwise known as humic substances) from land runoff. Culture studies were conducted to investigate the potential nutritive influence of DOM on G. catenatum. Using a seawater-based growth medium (28&#8240; salinity), enriched with nutrients but no DOM, the trace element selenium (as 10-9 M selenite) limited growth rate and biomass (cell density and chlorophyll a). Addition of standard humic acid (aquatic Suwannee River Humic Acid available from the International Humic Substances Society; SHA) caused a 5-25 and 30-90% decrease in G. catenatum growth and biomass, respectively. In contrast, growth and biomass of G. catenatum were increased by approximately 15 and 30-60%, respectively, when Suwannee River SHA and natural DOM (isolated from Huon River water, south-east Tasmania, by ultrafiltration) were added to cultures in the absence of any other chelators or associated trace metals. Under these conditions, biomass was limited by the macronutrients nitrate and phosphate suggesting that dissolved organic substances can change overall nutrient availability and/or uptake by G. catenatum, either by addition of nutrients (e.g. nitrogen and phosphorus) to the system, or by interaction with other nutrients (e.g. selenium). The importance of selenium for G. catenatum growth, its introduction into coastal systems in land runoff, and the interaction of selenium with DOM supports the widely accepted hypothesis that dissolved organic substances alter the supply of nutrients available for algal growth. From these observations it is clear that the outcome of DOM-nutrient interactions on algal growth is variable, and depends on the composition and amount of DOM, the concentration of nutrients in solution and the species- or strain-specific cellular nutrient...
Doblin, M.A. & Clayton, M.N. 1995, 'Effects of secondarily-treated sewage effluent on the early life-history stages of two species of brown macroalgae: Hormosira banksii and Durvillaea potatorum', Marine Biology, vol. 122, no. 4, pp. 689-698.
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Sewage effluent has a deleterious effect on the early life-history stages of Hormosira banksii (Turner) Decaisne and Durvillaea potatorum (Labillardi&egrave;re) Areschoug. High concentrations of sewage effluent (28 and 40% in seawater) inhibit zygote germination by 55 to 95%, retard embryo growth (80 to 100%) and cause severe embryo mortality, with less than 60 and 5% surviving after 14 d, respectively. It is probable that such adverse effects would significantly reduce levels of recruitment of these species in sewage-affected localities, and that sewage effluent has played an important role in the decline of these species from several rock platforms in south-east Victoria, Australia. Zygote germination, embryo growth and embryo mortality were inhibited ?40% more strongly in sewage effluent than diluted seawater, showing that the effect of sewage effluent is not simply one of seawater dilution. However, this effect was only observed at high concentrations (28 and 40%). The absence of any difference between the low concentrations of sewage effluent (4 and 12% in seawater) and diluted seawater suggests that the dilution of waste water is important in mitigating its more harmful effects. The sensitivity of H. banksii and D. potatorum embryos to the composition of the medium in which they grow and the ease with which they can be manipulated in culture suggest that they may be utilised as biological indicators of water quality. &copy; 1995 Springer-Verlag.


Hallegraeff, G.M., Beardall, J., Brett, S., Doblin, M.A., Hosja, W., de Salas, M. & Thompson, P. www.oceanclimatechange.org.au 2009, Marine climate change in Australia: Impacts and adaptation responses: Phytoplankton, pp. 1-10, Australia.
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