Associate Professor Martina Doblin

Biography

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 diversity of living marine eukaryotes to improve our understanding of their role in the ocean;
  • 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 my knowledge about algae to yield a better understanding of the effects of a changing climate and human activities on the base of the foodweb.

Professional

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

  • Convenor, IMOS Bio-optical Working Group

  • Marine National Facility Chief Scientist

Media:
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
 
Phone
+61 2 9514 8307
Fax
+61 2 9514 4079
Room
CB04.05.50G

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

Can supervise: Yes

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

Conference Papers

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', Wageningen, The Netherlands, December 2010 in Euro ISRS Symposium 2010, ed J. Kaandorp, E. Meesters, R. Osinga, J. Verreth, T. Wijgerde, 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', Wageningen, The Netherlands, December 2010 in Euro ISRS Symposium 2010, ed J. Kaandorp, E. Meesters, R. Osinga, J. Verreth, T. Wijgerde, 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, August 2009.
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, July 2009.
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, July 2007.

Journal Articles

Everett, J., Baird, M.E., Roughan, M., Suthers, I. & 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 S) and Smoky Cape (31 S). Within the central EAC separation zone, positive surface Chl. a anomalies occurred 65% of the time when both wind-stress (sw) and bottom-stress (sB) 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 sW resulting in a 70% increase in surface Chl. a at some locations, when compared to downwelling-favourable sW. 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 S) contained P20% 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 Sea). These patterns of phytoplankton biomass show contrasting temporal dynamics north and south of the central EAC separation zone with more episodic upwelling-driven Chl. a anomalies to the north, compared with regular annual spring bloom dynamics to the south. We expect changes in the strength of the EAC to have greater influence on shelf phytoplankton dynamics to the north of the separation zone.
Laczka, O.F., Labbate, M. & Doblin, M.A. 2014, 'Application of an ELISA-type amperometric assay to the detection of Vibrio species with screenprinted electrodes', Analytical Methods, vol. 6, pp. 2020-2023.
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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 photo-protective 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.
Clark, J.S., Poore, A.G., 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 (20C and 28C). Embryo growth was reduced at 28C, 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.
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, no. 1, 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+0.20 ml individual-1 h-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.
Sackett, O.E., Petrou, K., Reedy, B.J., De Grazia, A., Hill, R., Doblin, M.A., Beardall, J., Ralph, P.J. & Heraud, P. 2013, 'Phenotypic plasticity of Southern Ocean diatoms: Key to success in the sea ice habitat?', PLoS One, vol. 8, no. 11, pp. e81185-1-e81185-12.
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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.
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, pp. 1-10.
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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.
Gobler, C.J., Lobanov, A.V., Tang, Y., Turanov, A.A., Zhang, Y., Doblin, M.A., Taylor, G.T., Grigoriev, I.V., Sanudo-Wilhelm, S.A. & Gladyshev, V.N. 2013, 'The central role of selenium in the biochemistry and ecology of the harmful pelagophyte, Aureococcus anophagefferens', The 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 consisted 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 495% 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.
Hallegraeff, G.M., Blackburn, S.I., Doblin, M.A. & Bolch, C. 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 C) and warm-temperate ecotypes (12+18 C), but these appear unrelated to ITS genotypes and PST toxin phenotypes.
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 degrees C and +6 degrees 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 (FV/FM). Nitrogen depletion yielded a partially reduced electron transport chain in which maximum fluorescence (FM) could only be obtained by adding 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). reoxidation curves showed the presence of QB nonreducing PSII centers under nitrogen depletion. Fast induction curves (FICs) and electron transport rates (ETRs) revealed slowing of the electrons transferred from the primary (QA) to the secondary (QB) quinone electron acceptors of PSII. The data presented show that nitrogen depletion in F. cylindrus leads to the formation of QB nonreducing PSII centers within the photosystem. On a physiological level, the formation of QB 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.
Gilbert, J.A., Hill, R., Doblin, M.A. & Ralph, P.J. 2012, 'Microbial consortia increase thermal tolerance of corals', Marine Biology, vol. 159, 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 a and c-Proteobacteria. Corals were gradually heated from the control temperature of 26 to 31 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 FV/FM, typical of thermal stress. However, heated corals treated with antibiotics showed severe tissue loss in addition to a decline in FV/ FM. 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.
Sinutok, S., Hill, R., Doblin, M.A., Kuhl, 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, pp. 1201-1213.
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The effects of elevated CO 2 and temperature on photosynthesis and calcification of two important calcifying reef algae (Halimedamacroloba and Halimeda cylindracea) were investigated with O 2 microsensors and chlorophyll a fluorometry through a combination of two pCO 2 (400 and 1,200 atm) and two temperature treatments (28 and 32 C) equivalent to the present and predicted conditions during the 2100 austral summer. Combined exposure to pCO 2 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 O 2 production and a threefold reduction in calcification rate in the elevated CO 2 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 CO 2 and temperature in both species, where exposure to elevated CO 2 or temperature alone decreased photosynthesis and calcification, but exposure to both elevated CO 2 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.
Seymour, J.R., Doblin, M.A., Jeffries, T.C., Brown, M.V., Newton, K., Ralph, P.J., Baird, M.E. & Mitchell, J.G. 2012, 'Contrasting microbial assemblages in adjacent water masses associated with the East Australian Current', Environmental Microbiology Reports, vol. 4, 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
Baird, M.E., Suthers, I., Griffin, D.A., Hollings, B., Pattiaratchi, C.B., Everett, J., Roughan, M., Oubelkheir, K. & Doblin, M.A. 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.
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 carbonfixation 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.
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
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 degrees C, 30 degrees C, 32 degrees C, and 34 degrees 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 degrees C under all CO(2) levels, all species died. Chlorophyll (Chl) a and b concentration in Halimeda spp. significantly decreased in 203 Pa, 32 degrees C and 34 degrees 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 degrees 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 degrees C and 34 degrees C in all pH treatments). The rate of oxygen production 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 degrees 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.
Thompson, P., Bonham, P., Waite, A., Clementson, L., Cherukuru, N., Hassler, C.S. & 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 degrees and 34.51S latitude.
Hassler, C.S., Djajadikarta, J., Doblin, M.A., Everett, J. & Thompson, P. 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).
Doblin, M.A., Petrou, K., 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 30 m. 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.
Earp, A.A., Hanson, C.E., Ralph, P.J., Brando, V.E., Allen, S., Baird, M.E., Clementson, L., Daniel, P., Dekker, A.G., Fearns, P.R., Parslow, J.S., 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 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.
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 sur
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.
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 - 26%, 54 - 40% and 59 - 38% replacement with mid-ocean water to be within ocean baseline concentration ranges.
Gribben, P.E., Wright, J.T., O'Connor, W.A., Doblin, M.A., Eyre, B. & Steinberg, P. 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.
Fahnenstiel, G., Hong, Y., Millie, D., Doblin, M.A., Johengen, T. & Reid, D. 2009, 'Marine dinoflagellate cysts in the ballast tank sediments of ships entering the Laurentian Great Lakes', Verhandlungen Internationale Verein Limnology, vol. 30, no. 7, pp. 1035-1038.
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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 0.0008 psu yr+1. All stations showed positive trends in temperature, with the fastest surface warming (0.0202C 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.
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
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, 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.
Gilbert, P.M., Azanza, R., Burford, M.A., 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.A., Drennen, T., Dyhrman, S., Fukuyo, Y., Furnas, M., Galloway, J., Graneli, E., Ha, D., Hallegraeff, G.M., Harrison, J., Harrison, P., Heil, C.A., Heimann, K., Howarth, R., Jauzein, M., Kana, A.A., Kana, T.M., Kim, H., Kudela, R., Legrand, C., Mallin, M., Mulholland, M., Murray, S.A., 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. - 2008 Elsevier Ltd. All rights reserved.
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 undertsnading of th 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 and 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 ina varierty of ways. Using temperature tolerence as a measure of survivability and the temperature difference between ballst-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 thePort of Hampton Roads in lower Chesapeake Bay shows on the order of 10 20 microorganisms are discharged annually into the region.
Ralph, P.J., Durako, M.J., Enriquez, S., Collier, C. & 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.
Doblin, M.A., Coyne, K.J., Rinta-kanto, J., Wilhelm, S. & 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 weas detected in ballast water at intermidiate and final ports of call in all three experiemnts, 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 mucrocystin synthetase gene, mcyE, in ballst tanks indicated entrained cells were capable of producing mycrocystin, 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 bllom (HAB) species to distant ports in the world's largest freshwater resevoir, 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.
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 potenti
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 Sacramen
Doblin, M.A., Thompson, P.A., Revill, A.T., Butler, E.C., 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).
Willhelm, 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 Anayses 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 sturcture of marine microbisal food webs, few studies have directly addresed their role in large lake systems. As part of an ongoing study of the microbial acology of Lake Erie, we have examined the distribution and diversity of viruses in this system. One surprising result has bee the pervasive distribution of cyanophages that infect the marine cyanobacterial isolate Synechococcus sp. strain WH7803. Viruses that typically infect this cyanobacterium wre 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.
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, 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 of the generation of standard curves from plasmids or laboratory cultures that may be unrealistic whencompared 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 awways for two HAB species, Chattonella subsala and Heterosigma akashiwo, in which we introduce a known concentration of exogenous DNA plasmid into the extraction buffer as a refernce 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 application 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 smaples, Out 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.
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 behaviour of harmful raphidophytes in the Delaware Inland Bays utilizing quantitative real-time PCR', Aquatic Microbial Ecology, vol. 40, 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 ti 2m) Delaware Inland Bays (DIB), USA. Raphidophytes vertically migrate in other deeper water ecosystems to utilise 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 characterise and understamd the migration oatterns of DIB raphidiphytes, 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 inthe response of C. subsalsa and H. akashiwo to light:dark period manipulations suggested possible diffeerneces in external versus endogenous regulation of migration behaviour in the 2 species. Natural blooms in the filed (enclosed in a mesocosm system) also exhibited patterns of 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 behaviour 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 poweful tool for fine spatial temporal scale detection and enum,eration of vertically migrating harmful algal species.
Drake, L.A., Meyer, A.E., Forsberg, R.L., Baier, R.E., Doblin, M.A., Heinemann, S.H., Johnson, W.P., Koch, M., Roblee, 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, 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 invatsions is the potential for biofilms within ships' ballast water tanks to harbour pathogens, and, in tuen, seed othe waters. To begin to evaluate this vector, we collected biofilm samples fromtanks' 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 ballst 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.
Doblin, M.A., Coyne, K.J., Popels, L.C., 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 (similar to2 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.K., 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-mum 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 & 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 mug 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.
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. 4A, 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 mum, and greater than or equal to2,000 mum. Selenium values ranged 1.02-6.07 mug 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 correlated 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.
Laroussi, M., Dobbs, F.C., Wei, Z., Doblin, M.A., Ball, L.G., Moreira, K., Dyer, F. & Richardson, J. 2002, 'Decontamination of water by excimer UV radiation', IEEE Transactions On Plasma Science, vol. 30, no. 4, 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 im
Baines, S.B., Fisher, N.K., 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 functio
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-en
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 f
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 humi
Doblin, M.A. & Clayton, M.N. 1995, 'Effects Of Secondarily Treated Sewage Effluent On The Early Life-History Stages Of 2 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 Hosmosira banksii (Turner) Decaisne and Durvillaea potatorum (Labillardiere) Areschoug. High concentrations of sewage effluent (28 and 40% in seawater) inhibit zygote germinatio

Reports

Hallegraeff, G.M., Beardall, J., Brett, S., Doblin, M.A., Hosja, W., de Salas, M. & Thompson, P. 2009, 'Marine climate change in Australia: Impacts and adaptation responses: Phytoplankton', www.oceanclimatechange.org.au, Australia, pp. 1-10.
Salas, M.d., Cheal, A., Lough, J., McKinnon, D., Meekan, M., Sweatman, H., Coleman, M., Chambers, L., Dunlop, N., Church, J., Dowdney, J., Feng, M., Griffiths, S., Hobday, A., Matear, R., Poloczanska, E., Richardson, A., Ridgway, K., Risbey, J., Thompson, P., Thresher, R., Weller, E., Saintilan, N., Wilson, S., Lenanton, R., Hosja, W., Moore, P., Wernberg, T., Marshall, P.D., Connolly, R., Hill, K., Congdon, B., Devney, C., Fuentes, M., Graham, N., Hamann, M., Kingsford, M., Munday, P., Pratchett, M., Sheaves, M., Beardall, J., Brett, S., Waschka, M., Dann, P., Edgar, G., Swadling, K., Connell, S., Russell, B., Ward, T., Lukoschek, V., McGregor, S., Jenkins, G., Campbell, A., Steinberg, P., Anthony, K., Lovelock, C., Skilleter, G., Figueira, W.F., Booth, D.J., Doblin, M.A., Davidson, J., Holbrook, N., Howard, W., Kendrick, G. & Smale, D. 2009, 'Report Card of Marine Climate Change for Australia', NCCARF Publication, Australia, pp. 1-2.