I am a senior lecturer in the School of Life Sciences (SoLS), Program Director BSc Marine Biology and leader of the Marine Microphycology Lab (MML).
Our research in the MML is focused on understanding phytoplankton physiology and DMSP ecology in a changing world. Through coupling photobiology with biochemistry we aim to advance the understanding of phytoplankton phenotypic plasticity and how it influences ocean functioning, phototrophic inter-organism interactions (phytoplankton-bacteria) and symbioses (dinoflagellates-cnidarian; microalgal-protist). Specifically, our research tries to uncover the role of biogenic sulphur in microalgal physiology and its influence on marine productivity, social networks and biological partnerships. Our research spans a broad range of organisms (phytoplankton, corals, foraminifera) and diverse habitats (coral reefs, temperate coastal waters, Antarctic waters, sea ice), examining these responses, processes and interactions at various spatial and temporal scales.
To find out more, please visit my webpage.
Current members of MML:
Dr Stephanie Gardner - PhD Candidate (completed)
Ms Cristin Sheehan - PhD Candidate
Ms Eva Fernandez - PhD Candidate
Mr James O'Brien - PhD Candidate
Ms Michelle Havlik - Honours student
Stephanie Gardner - The ecophysiology of dimethylsulphoniopropionate (DMSP) in coral reef ecosystems: from cells to communities (co-supervised by Prof. Peter Ralph and Dr Jean-Baptiste Raina).
Cristin Sheehan - Life in the freezer: the role of dimethylsulphoniopropionate (DMSP) in the physiological and biochemical adaptations of Antarctic microalgae (co-supervised by Prof. Peter Ralph)
Eva Fernandez - Sulphur-mediated phytoplankton ecophysiology: the role of dimethylsulphoniopropionate (DMSP) in cellular function and marine microbial foodwebs (co-supervised by Assoc. Prof. Justin Seymour)
James O'Brien - Sulphur-mediated marine microbial interactions (co-supervised by Assoc. Prof. Justin Seymour)
Alicia Cook - When the heat is on: the effect of repeated stress and history of heat stress on stress recovery and performance in desert plants (Principle supervisor Assoc. Prof. Andrea Leigh)
Michelle Havlik - Does the osmotrophic uptake of DMSP enhance Antarctic phytoplankton productivity? (2017)
James O'Brien - Emiliania huxleyi: sulphur-mediated microbial interactions under mesoscale oceanographic perturbations (2016)
Isobel Cummings - Fading Fossils: the fate of foraminifera in a future ocean (2014)
Simon Hardy - The effect of temperature on carbon stores in seagrass habitat (2014)
Fabio Ramos - Assessing the ecological interactions between marine bacteria and phytoplankton (2013)
Cristin Sheehan - Sunlight through glasshouses: understanding diatom physiology and productivity under a changing climate (2013)
- Australian Marine Sciences Association
- Australian Coral Reef Society
- Australasian Society for Phycology and Aquatic Botany
Can supervise: YES
The fundamental goal of my research is to characterise phytoplankton phenotypic plasticity to environmental change and understand the role it plays in influencing marine productivity and phototrophic inter-organism interactions. Underpinning my research is the understanding that shifts in phytoplankton physiology can disrupt ocean function and species interactions, which can profoundly affect productivity, biogeochemistry and ecology of marine organisms and ocean ecosystems.
My key research themes are:
Phytoplankton phenotypic plasticity: Characterising phenotypic traits of different phytoplankton taxa to help answer questions about which taxonomic groups and individual species will benefit from future ocean conditions and transform our understanding of how physiological plasticity modulates the functionality of phytoplankton in a changing environment.
Phytoplankton physiology: Understanding photosynthetic stress and sulphur production with respect to its role in oxidative stress and antioxidant processes in photoautotrophs, including phytoplankton, corals, macroalgae and foraminifera.
Phytoplankton-bacteria interactions: Determining how phytoplankton physiological condition influences bacterial associations at different spatial scales (micro-oceanographic). Specifically, how changes in the production and sensing of chemical cues (like DMSP) regulate these marine microbial interactions.
Marine microalgal symbioses (host-symbiont interactions): Investigating coral health at the cnidarian-dinoflagellate (cell-cell) interface - utilising single cell methods (epifluorescence microscopy, microscope fluorometry, infra-red microspectroscopy) to examine the physiological and biochemical responses that occur at the cellular scale.
Exploring phototaxis of endosymbionts in foraminifera - exploring the possible role of host-mediated symbiont shuffling in the regulation of photosynthesis and calcification.
Examining the physiological and biochemical link between sulphur (DMSP) and oxidative stress in corals and foraminifera to determine the role of DMSP production in the molecular and physiological response of the photosymbiotic organism to thermal stress.
Subject Coordinator and Chief Lecturer for Marine Communities (91157)
Guest Lecturer for the Biocomplexity (91123)
Deppeler, S., Petrou, K., Schulz, K.G., Westwood, K., Pearce, I., McKinlay, J. & Davidson, A. 2018, 'Ocean acidification of a coastal Antarctic marine microbial community reveals a critical threshold for CO2 tolerance in phytoplankton productivity', Biogeosciences, vol. 15, no. 1, pp. 209-231.View/Download from: Publisher's site
© 2017 Author. High-latitude oceans are anticipated to be some of the first regions affected by ocean acidification. Despite this, the effect of ocean acidification on natural communities of Antarctic marine microbes is still not well understood. In this study we exposed an early spring, coastal marine microbial community in Prydz Bay to CO 2 levels ranging from ambient (343atm) to 1641atm in six 650 L minicosms. Productivity assays were performed to identify whether a CO 2 threshold existed that led to a change in primary productivity, bacterial productivity, and the accumulation of chlorophyll a (Chl a) and particulate organic matter (POM) in the minicosms. In addition, photophysiological measurements were performed to identify possible mechanisms driving changes in the phytoplankton community. A critical threshold for tolerance to ocean acidification was identified in the phytoplankton community between 953 and 1140atm. CO 2 levels 1140atm negatively affected photosynthetic performance and Chl a-normalised primary productivity (csGPP 14C ), causing significant reductions in gross primary production (GPP 14C ), Chl a accumulation, nutrient uptake, and POM production. However, there was no effect of CO 2 on C VN ratios. Over time, the phytoplankton community acclimated to high CO 2 conditions, showing a down-regulation of carbon concentrating mechanisms (CCMs) and likely adjusting other intracellular processes. Bacterial abundance initially increased in CO 2 treatments 953atm (days 3-5), yet gross bacterial production (GBP14C) remained unchanged and cell-specific bacterial productivity (csBP14C) was reduced. Towards the end of the experiment, GBP14C and csBP14C markedly increased across all treatments regardless of CO 2 availability. This coincided with increased organic matter availability (POC and PON) combined with improved efficiency of carbon uptake. Changes in phytoplankton community production could have negative effects on the Antarctic food web a...
Ocean warming is resulting in increased occurrence of mass coral bleaching; a response in which the intracellular algal endosymbionts (Symbiodinium sp.) are expelled from the coral host due to physiological stress. This detrimental process is often attributed to overproduction of reactive oxygen species (ROS) that leak out of the endosymbionts and causes damage to the host cell, though direct evidence validating this link is limited. Here, for the first time, we used confocal microscopy and fluorescent dyes to investigate if endosymbiont ROS production significantly and predictably affects physiological parameters in its host cell. Heat treatment resulted in a 60% reduction in coral symbiont density, a ~70% increase in median endosymbiont ROS and a small reduction in photosystem efficiency (FV/FM, 11%), indicating absence of severe light stress. Notably, no other physiological parameters were affected in either endosymbionts or host cells, including reduced glutathione and ROS-induced lipid peroxidation. Taken together, the increase in endosymbiont ROS could not be linked to physiological damage in either partner, suggesting that oxidative stress is unlikely to have been the driver for symbiont expulsion in this study.
Petrou, K., Nielsen, D.A. & Heraud, P. 2018, 'Single-cell biomolecular analysis of coral algal symbionts reveals opposing metabolic responses to heat stress and expulsion', Frontiers in Marine Science, vol. 5, no. MAR.View/Download from: Publisher's site
© 2018 Petrou, Nielsen and Heraud. The success of corals in nutrient poor environments is largely attributed to the symbiosis between the cnidarian host and its intracellular alga. Warm water anomalies have been shown to destabilize this symbiosis, yet detailed analysis of the effect of temperature and expulsion on cell-specific carbon and nutrient allocation in the symbiont is limited. Here, we exposed colonies of the hard coral Acropora millepora to heat stress and using synchrotron-based infrared microspectroscopy measured the biomolecular profiles of individual in hospite and expelled symbiont cells at an acute state of bleaching. Our results showed symbiont metabolic profiles to be remarkably distinct with heat stress and expulsion, where the two effectors elicited opposing metabolic adjustments independent of treatment or cell type. Elevated temperature resulted in biomolecular changes reflecting cellular stress, with relative increases in free amino acids and phosphorylation of molecules and a concomitant decline in protein content, suggesting protein modification and degradation. This contrasted with the metabolic profiles of expelled symbionts, which showed relative decreases in free amino acids and phosphorylated molecules, but increases in proteins and lipids, suggesting expulsion lessens the overall effect of heat stress on the metabolic signature of the algal symbionts. Interestingly, the combined effects of expulsion and thermal stress were additive, reducing the overall shifts in all biomolecules, with the notable exception of the significant accumulation of lipids and saturated fatty acids. This first use of a single-cell metabolomics approach on the coral symbiosis provides novel insight into coral bleaching and emphasizes the importance of a single-cell approach to demark the cell-to-cell variability in the physiology of coral cellular populations.
Gardner, S.G., Raina, J.-.B., Nitschke, M.R., Nielsen, D.A., Stat, M., Motti, C.A., Ralph, P.J. & Petrou, K. 2017, 'A multi-trait systems approach reveals a response cascade to bleaching in corals.', BMC biology, vol. 15, no. 1, p. 117.View/Download from: UTS OPUS or Publisher's site
Climate change causes the breakdown of the symbiotic relationships between reef-building corals and their photosynthetic symbionts (genus Symbiodinium), with thermal anomalies in 2015-2016 triggering the most widespread mass coral bleaching on record and unprecedented mortality on the Great Barrier Reef. Targeted studies using specific coral stress indicators have highlighted the complexity of the physiological processes occurring during thermal stress, but have been unable to provide a clear mechanistic understanding of coral bleaching.Here, we present an extensive multi-trait-based study in which we compare the thermal stress responses of two phylogenetically distinct and widely distributed coral species, Acropora millepora and Stylophora pistillata, integrating 14 individual stress indicators over time across a simulated thermal anomaly. We found that key stress responses were conserved across both taxa, with the loss of symbionts and the activation of antioxidant mechanisms occurring well before collapse of the physiological parameters, including gross oxygen production and chlorophyll a. Our study also revealed species-specific traits, including differences in the timing of antioxidant regulation, as well as drastic differences in the production of the sulfur compound dimethylsulfoniopropionate during bleaching. Indeed, the concentration of this antioxidant increased two-fold in A. millepora after the corals started to bleach, while it decreased 70% in S. pistillata.We identify a well-defined cascading response to thermal stress, demarking clear pathophysiological reactions conserved across the two species, which might be central to fully understanding the mechanisms triggering thermally induced coral bleaching. These results highlight that bleaching is a conserved mechanism, but specific adaptations linked to the coral's antioxidant capacity drive differences in the sensitivity and thus tolerance of each coral species to thermal stress.
Gardner, S.G., Raina, J.-.B., Ralph, P.J. & Petrou, K. 2017, 'Reactive oxygen species (ROS) and dimethylated sulphur compounds in coral explants under acute thermal stress.', Journal of Experimental Biology, vol. 220, no. Pt 10, pp. 1787-1791.View/Download from: UTS OPUS or Publisher's site
Coral bleaching is intensifying with global climate change. Although the causes for these catastrophic events are well understood, the cellular mechanism that triggers bleaching is not well established. Our understanding of coral bleaching processes is hindered by the lack of robust methods for studying interactions between host and symbiont at the single-cell level. Here, we exposed coral explants to acute thermal stress and measured oxidative stress, more specifically, reactive oxygen species (ROS), in individual symbiont cells. Furthermore, we measured concentrations of dimethylsulphoniopropionate (DMSP) and dimethylsulphoxide (DMSO) to elucidate the role of these compounds in coral antioxidant function. This work demonstrates the application of coral explants for investigating coral physiology and biochemistry under thermal stress and delivers a new approach to study host-symbiont interactions at the microscale, allowing us to directly link intracellular ROS with DMSP and DMSO dynamics.
Macreadie, P.I., Nielsen, D.A., Kelleway, J.J., Atwood, T.B., Seymour, J.R., Petrou, K., Connolly, R.M., Thomson, A.C.G., Trevathan-Tackett, S.M. & Ralph, P.J. 2017, 'Can we manage coastal ecosystems to sequester more blue carbon?', Frontiers in Ecology and the Environment, vol. 15, no. 4, pp. 206-213.View/Download from: UTS OPUS or Publisher's site
© The Ecological Society of America To promote the sequestration of blue carbon, resource managers rely on best-management practices that have historically included protecting and restoring vegetated coastal habitats (seagrasses, tidal marshes, and mangroves), but are now beginning to incorporate catchment-level approaches. Drawing upon knowledge from a broad range of environmental variables that influence blue carbon sequestration, including warming, carbon dioxide levels, water depth, nutrients, runoff, bioturbation, physical disturbances, and tidal exchange, we discuss three potential management strategies that hold promise for optimizing coastal blue carbon sequestration: (1) reducing anthropogenic nutrient inputs, (2) reinstating top-down control of bioturbator populations, and (3) restoring hydrology. By means of case studies, we explore how these three strategies can minimize blue carbon losses and maximize gains. A key research priority is to more accurately quantify the impacts of these strategies on atmospheric greenhouse-gas emissions in different settings at landscape scales.
Petrou, K., Ralph, P.J. & Nielsen, D.A. 2017, 'A novel mechanism for host-mediated photoprotection in endosymbiotic foraminifera.', ISME Journal, vol. 11, no. 2, pp. 453-462.View/Download from: Publisher's site
Light underpins the health and function of coral reef ecosystems, where symbiotic partnerships with photosynthetic algae constitute the life support system of the reef. Decades of research have given us detailed knowledge of the photoprotective capacity of phototrophic organisms, yet little is known about the role of the host in providing photoprotection in symbiotic systems. Here we show that the intracellular symbionts within the large photosymbiotic foraminifera Marginopora vertebralis exhibit phototactic behaviour, and that the phototactic movement of the symbionts is accomplished by the host, through rapid actin-mediated relocation of the symbionts deeper into the cavities within the calcium carbonate test. Using a photosynthetic inhibitor, we identified that the infochemical signalling for host regulation is photosynthetically derived, highlighting the presence of an intimate communication between the symbiont and the host. Our results emphasise the central importance of the host in photosymbiotic photoprotection via a new mechanism in foraminifera that can serve as a platform for exploring host-symbiont communication in other photosymbiotic organisms.
Alacid, E., Park, M.G., Turon, M., Petrou, K. & Garcés, E. 2016, 'A Game of Russian Roulette for a Generalist Dinoflagellate Parasitoid: Host Susceptibility Is the Key to Success.', Frontiers in Microbiology, vol. 7, pp. 1-13.View/Download from: UTS OPUS or Publisher's site
Marine microbial interactions involving eukaryotes and their parasites play an important role in shaping the structure of phytoplankton communities. These interactions may alter population densities of the main host, which in turn may have consequences for the other concurrent species. The effect generalist parasitoids exert on a community is strongly dependent on the degree of host specificity. Parvilucifera sinerae is a generalist parasitoid able to infect a wide range of dinoflagellates, including toxic-bloom-forming species. A density-dependent chemical cue has been identified as the trigger for the activation of the infective stage. Together these traits make Parvilucifera-dinoflagellate hosts a good model to investigate the degree of specificity of a generalist parasitoid, and the potential effects that it could have at the community level. Here, we present for the first time, the strategy by which a generalist dinoflagellate parasitoid seeks out its host and determine whether it exhibits host preferences, highlighting key factors in determining infection. Our results demonstrate that in its infective stage, P. sinerae is able to sense potential hosts, but does not actively select among them. Instead, the parasitoids contact the host at random, governed by the encounter probability rate and once encountered, the chance to penetrate inside the host cell and develop the infection strongly depends on the degree of host susceptibility. As such, their strategy for persistence is more of a game of Russian roulette, where the chance of survival is dependent on the susceptibility of the host. Our study identifies P. sinerae as a potential key player in community ecology, where in mixed dinoflagellate communities consisting of hosts that are highly susceptible to infection, parasitoid preferences may mediate coexistence between host species, reducing the dominance of the superior competitor. Alternatively, it may increase competition, leading to species exclusion. I...
Baird, M.E., Adams, M.P., Babcock, R.C., Oubelkheir, K., Mongin, M., Wild-Allen, K.A., Skerratt, J., Robson, B.J., Petrou, K., Ralph, P.J., O'Brien, K.R., Carter, A.B., Jarvis, J.C. & Rasheed, M.A. 2016, 'A biophysical representation of seagrass growth for application in a complex shallow-water biogeochemical model', ECOLOGICAL MODELLING, vol. 325, pp. 13-27.View/Download from: Publisher's site
Doblin, M.A., Petrou, K., Sinutok, S., Seymour, J.R., Messer, L.F., Brown, M.V., Norman, L., Everett, J.D., McInnes, A.S., Ralph, P.J., Thompson, P.A. & Hassler, C.S. 2016, 'Nutrient uplift in a cyclonic eddy increases diversity, primary productivity and iron demand of microbial communities relative to a western boundary current', PEERJ, vol. 4.View/Download from: UTS OPUS or Publisher's site
Gardner, S.G., Nielsen, D.A., Laczka, O., Shimmon, R., Beltran, V.H., Ralph, P.J. & Petrou, K. 2016, 'Dimethylsulfoniopropionate, superoxide dismutase and glutathione as stress response indicators in three corals under short-term hyposalinity stress', PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES, vol. 283, no. 1824.View/Download from: UTS OPUS or Publisher's site
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', ENVIRONMENTAL MICROBIOLOGY REPORTS, vol. 8, no. 2, pp. 235-238.View/Download from: Publisher's site
Petrou, K., Kranz, S.A., Trimborn, S., Hassler, C.S., Ameijeiras, S.B., Sackett, O., Ralph, P.J. & Davidson, A.T. 2016, 'Southern Ocean phytoplankton physiology in a changing climate', JOURNAL OF PLANT PHYSIOLOGY, vol. 203, pp. 135-150.View/Download from: UTS OPUS or Publisher's site
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.', The ISME journal, vol. 10, pp. 416-426.View/Download from: UTS OPUS or Publisher's site
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.The ISME Journal advance online publication, 31 July 2015; doi:10.1038/ismej.2015.123.
Hill, R., Bellgrove, A., Macreadie, P.I., Petrou, K., Beardall, J., Steven, A. & Ralph, P.J. 2015, 'Can macroalgae contribute to blue carbon? An Australian perspective', LIMNOLOGY AND OCEANOGRAPHY, vol. 60, no. 5, pp. 1689-1706.View/Download from: Publisher's site
Tout, J., Jeffries, T.C., Petrou, K., Tyson, G.W., Webster, N.S., Garren, M., Stocker, R., Ralph, P.J. & Seymour, J.R. 2015, 'Chemotaxis by natural populations of coral reef bacteria', ISME JOURNAL, vol. 9, no. 8, pp. 1764-1777.View/Download from: UTS OPUS or Publisher's site
Curtis, E.M., Knight, C., Petrou, K. & Leigh, A. 2014, 'A comparative analysis of photosynthetic recovery from thermal stress: a desert plant case study', Oecologia, vol. 175, pp. 1051-1061.View/Download from: UTS OPUS or Publisher's site
Our understanding of the effects of heat stress on plant photosynthesis has progressed rapidly in recent years through the use of chlorophyll a fluorescence techniques. These methods frequently involve the treatment of leaves for several hours in dark conditions to estimate declines in maximum quantum yield of photsystem II (FV/FM), rarely accounting for the recovery of effective quantum yield (?F/FM') after thermally induced damage occurs. Exposure to high temperature extremes, however, can occur over minutes, rather than hours, and recent studies suggest that light influences damage recovery. Also, the current focus on agriculturally important crops may lead to assumptions about average stress responses and a poor understanding about the variation among species thermal tolerance. We present a chlorophyll a fluorescence protocol incorporating subsaturating light to address whether species thermal tolerance thresholds (T50) are related to the ability to recover from short-term heat stress in 41Australian desert species. We found that damage incurred by 15-min thermal stress events was most strongly negatively correlated with the capacity of species to recover after a stress event of 50 °C in summer. Phylogenetically independent contrast analyses revealed that basal divergences partially explain this relationship. Although T50 and recovery capacity were positively correlated, the relationship was weaker for species with high T50 values (>51 °C). Results highlight that, even within a single desert biome, species vary widely in their physiological response to high temperature stress and recovery metrics provide more comprehensive information than damage metrics alone.
Petrou, K., Belgio, E. & Ruban, A.V. 2014, 'pH sensitivity of chlorophyll fluorescence quenching is determined by the detergent/protein ratio and the state of LHCII aggregation', Biochimica et Biophysica Acta (BBA) - Bioenergetics, vol. 1837, no. 9, pp. 1533-1539.View/Download from: UTS OPUS or Publisher's site
Here we show how the protein environment in terms of detergent concentration/protein aggregation state, affects the sensitivity to pH of isolated, native LHCII, in terms of chlorophyll fluorescence quenching. Three detergent concentrations (200, 20 and 6 µM n-dodecyl -d-maltoside) have been tested. It was found that at the detergent concentration of 6 µM, low pH quenching of LHCII is close to the physiological response to lumen acidification possessing pK of 5.5. The analysis has been conducted both using arbitrary PAM fluorimetry measurements and chlorophyll fluorescence lifetime component analysis. The second led to the conclusion that the 3.5 ns component lifetime corresponds to an unnatural state of LHCII, induced by the detergent used for solubilising the protein, whilst the 2 ns component is rather the most representative lifetime component of the conformational state of LHCII in the natural thylakoid membrane environment when the non-photochemical quenching (NPQ) was absent. The 2 ns component is related to a pre-aggregated LHCII that makes it more sensitive to pH than the trimeric LHCII with the dominating 3.5 ns lifetime component. The pre-aggregated LHCII displayed both a faster response to protons and a shift in the pK for quenching to higher values, from 4.2 to 4.9. We concluded that environmental factors like lipids, zeaxanthin and PsbS protein that modulate NPQ in vivo could control the state of LHCII aggregation in the dark that makes it more or less sensitive to the lumen acidification. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: Keys to Produce Clean Energy.
Petrou, K., Trimborn, S., Rost, B., Ralph, P.J. & Hassler, C.S. 2014, 'The impact of iron limitation on the physiology of the Antarctic diatom Chaetoceros simplex', Marine Biology, vol. 161, pp. 925-937.View/Download from: UTS OPUS or Publisher's site
Iron availability strongly governs the growth of Southern Ocean phytoplankton. To investigate how iron limitation affects photosynthesis as well as the uptake of carbon and iron in the Antarctic diatom Chaetoceros simplex, a combination of chlorophyll a fluorescence measurements and radiotracer incubations in the presence and absence of chemical inhibitors was conducted. Iron limitation in C. simplex led to a decline in growth rates, photochemical efficiency and structural changes in photosystem II (PSII), including a reorganisation of photosynthetic units in PSII and an increase in size of the functional absorption cross section of PSII. Iron-limited cells further exhibited a reduced plastoquinone pool and decreased photosynthetic electron transport rate, while non-photochemical quenching and relative xanthophyll pigment content were strongly increased, suggesting a photoprotective response. Additionally, iron limitation resulted in a strong decline in carbon fixation and thus the particulate organic carbon quotas. Inhibitor studies demonstrated that, independent of the iron supply, carbon fixation was dependent on internal, but not on extracellular carbonic anhydrase activity. Orthovanadate more strongly inhibited iron uptake in iron-limited cells, indicating that P-type ATPase transporters are involved in iron uptake. The stronger reduction in iron uptake by ascorbate in iron-limited cells suggests that the re-oxidation of iron is required before it can be taken up and further supports the presence of a high-affinity iron transport pathway. The measured changes to photosystem architecture and shifts in carbon and iron uptake strategies in C. simplex as a result of iron limitation provide evidence for a complex interaction of these processes to balance the iron requirements for photosynthesis and carbon demand for sustained growth in iron-limited waters.
Trimborn, S., Thoms, S., Petrou, K., Kranz, S.A. & Rost, B. 2014, 'Photophysiological responses of Southern Ocean phytoplankton to changes in CO2 concentrations: Short-term versus acclimation effects', Journal Of Experimental Marine Biology And Ecology, vol. 451, pp. 44-54.View/Download from: UTS OPUS or Publisher's site
The present study examines how different pCO2 acclimations affect the CO2- and light-dependence of photophysiological processes and O2 fluxes in four Southern Ocean (SO) key phytoplankton species. We grew Chaetoceros debilis (Cleve), Pseudo-nitzschia subcurvata (Hasle), Fragilariopsis kerguelensis (O'Meara) and Phaeocystis antarctica (Karsten) under low (160 µatm) and high (1000 µatm) pCO2. The CO2- and light-dependence of fluorescence parameters of photosystem II (PSII) were determined by means of a fluorescence induction relaxation system (FIRe). In all tested species, nonphotochemical quenching (NPQ) is the primary photoprotection strategy in response to short-term exposure to high light or low CO2 concentrations. In C. debilis and P. subcurvata, PSII connectivity (p) and functional absorption cross-sections of PSII in ambient light (sPSII') also contributed to photoprotection while changes in re-oxidation times of Qa acceptor (tQa) were more significant in F. kerguelensis. The latter was also the only species being responsive to high acclimation pCO2, as these cells had enhanced relative electron transport rates (rETRs) and sPSII' while tQa and p were reduced under short-term exposure to high irradiance. Low CO2-acclimated cells of F. kerguelensis and all pCO2 acclimations of C. debilis and P. subcurvata showed dynamic photoinhibition with increasing irradiance. To test for the role and presence of the Mehler reaction in C. debilis and P. subcurvata, the light-dependence of O2 fluxes was estimated using membrane inlet mass spectrometry (MIMS). Our results show that the Mehler reaction is absent in both species under the tested conditions. We also observed that dark respiration was strongly reduced under high pCO2 in C. debilis while it remained unaltered in P. subcurvata. Our study revealed species-specific differences in the photophysiological responses to pCO2, both on the acclimation as well as the short-term level.
Garces, E., Alacid, E., Rene, A., Petrou, K. & Simo, R. 2013, 'Host-released dimethylsulphide activates the dinoflagellate parasitoid Parvilucifera sinerae', ISME Journal, vol. 7, pp. 1065-1068.View/Download from: UTS OPUS or Publisher's site
Parasitoids are a major top-down cause of mortality of coastal harmful algae, but the mechanisms and strategies they have evolved to efficiently infect ephemeral blooms are largely unknown. Here, we show that the generalist dinoflagellate parasitoid Parvilucifera sinerae (Perkinsozoa, Alveolata) is activated from dormancy, not only by Alexandrium minutum cells but also by culture filtrates. We unequivocally identified the algal metabolite dimethylsulphide (DMS) as the density-dependent cue of the presence of potential host. This allows the parasitoid to alternate between a sporangiumhosted dormant stage and a chemically-activated, free-living virulent stage. DMS-rich exudates of resistant dinoflagellates also induced parasitoid activation, which we interpret as an example of coevolutionary arms race between parasitoid and host. These results further expand the involvement of dimethylated sulphur compounds in marine chemical ecology, where they have been described as foraging cues and chemoattractants for mammals, turtles, birds, fish, invertebrates and plankton microbes.
Petrou, K., Jimenez-denness, I., Chartrand, K.M., Mccormack, C., Rasheed, M. & Ralph, P.J. 2013, 'Seasonal heterogeneity in the photophysiological response to air exposure in two tropical intertidal seagrass species', Marine Ecology Progress Series, vol. 482, pp. 93-106.View/Download from: UTS OPUS or Publisher's site
Photosynthesis, chlorophyll a fluorescence, leaf bio-optical properties and pigments were measured in 2 tropical intertidal seagrass species, Zostera muelleri ssp. capricorni and Halophila ovalis before, during and after air-exposure over a tidal cycle. Data were collected across 4 seasons (October and January-growing seasons; May and July-senescent seasons) to determine seasonal dynamics in physiological responses to air exposure. Both species showed clear light-dependent responses with a decline in photosynthetic efficiency and increased photoprotection during periods of combined maximum daily irradiance and air exposure for all seasons. In Z. muelleri ssp. capricorni there was a negative correlation between air-exposed effective quan - tum yield and light intensity, suggesting exposure was driving this decline. Conversely, sensitivity (decline in effective quantum yield of photosystem II) to increased irradiance dominated the response in H. ovalis, with no change in the magnitude of this response between air-exposed and submerged blades. The response to air exposure observed in Z. muelleri ssp. capricorni showed seasonal variation, with a greater decline in photosynthesis during the spring (October). Tidal exposure did not provide intertidal seagrasses a 'window' of photosynthetic respite (increase in photosynthesis) from high natural or anthropogenic turbidity. However, the periods immediately prior to and after exposure were important for providing an optimum period for net photosynthetic gain.
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.View/Download from: UTS OPUS or Publisher's site
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.View/Download from: UTS OPUS or Publisher's site
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.
Cassar, N., DiFiore, P.J., Barnett, B.A., Bender, M.L., Bowie, A.R., Tilbrook, B., Petrou, K., Westwood, K.J., Wright, S.W. & Lefevre, D. 2011, 'The influence of iron and light on net community production in the Subantarctic and Polar Frontal Zones', Biogeosciences, vol. 8, no. 2, pp. 227-237.View/Download from: UTS OPUS or Publisher's site
The roles of iron and light in controlling biomass and primary productivity are clearly established in the Southern Ocean. However, their influence on net community production (NCP) and carbon export remains to be quantified. To improve our understanding
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.View/Download from: UTS OPUS or Publisher's site
Marine primary production is a fundamental measure of the oceanâs 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.
Petrou, K. & Ralph, P.J. 2011, 'Photosynthesis and net primary productivity in three Antarctic diatoms: possible significance for their distribution in the Antarctic marine ecosystem', Marine Ecology Progress Series, vol. 437, pp. 27-40.View/Download from: UTS OPUS or Publisher's site
Photosynthesis and net primary productivity were measured in 3 Antarctic diatoms, Fragilariopsis cylindrus, Pseudo-nitzschia subcurvata and Chaetoceros sp., exposed to rapid changes in temperature and salinity representing a range of conditions found during a seasonal cycle. Measured differences in fluorescence-derived photosynthetic activity and oxygen evolution suggested that some alternative electron cycling activity was present under high irradiances. F. cylindrus displayed the highest rates of relative electron transport and net primary productivity under all salinity and temperature combinations and showed adaptive traits towards the sea-ice-like environment. P. subcurvata displayed a preference for low saline conditions where production rates were greatest. However, there was evidence of photosynthetic sensitivity to the lowest temperatures and highest salinities, suggesting a lack of adaptation for dealing with sea-ice-like conditions. Chaetoceros sp. showed high plasticity, acclimating well to all conditions but performing best under pelagic conditions. The study shows species-specific sensitivities to environmental change, highlighting photosynthetic capacity as a potentially important mechanism in ecological niche adaptation. When these data were modelled over different seasons, integrated daily net primary production was greatest under summer pelagic conditions. The findings from this study support the general observations of light control and seasonal development of net primary productivity and species succession in the Antarctic marine ecosystem.
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.View/Download from: UTS OPUS or Publisher's site
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 speciesâ 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 diatomsâFragilariopsis cylindrus, Pseudo-nitzschia subcurvata and Chaetoceros sp.âto 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 speciesâ distribution
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.View/Download from: UTS OPUS or Publisher's site
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., 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.View/Download from: UTS OPUS or Publisher's site
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., 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.View/Download from: UTS OPUS or Publisher's site
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 µmol photons m-2 s-1, 50 µmol photons m-2 s-1, 100 µmol photons m-2 s-1, and 200 µmol photons m-2 s-1). Photosynthetic capacity of photosystem II (PSII) dropped significantly over 3 h under 200 µmol photons m-2 s-1, but largely recovered when placed in a low-light environment (10 µmol 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 µmol 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.
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.View/Download from: UTS OPUS or Publisher's site
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.
Ralph, P.J., Wilhelm, C., Lavaud, J., Jakob, T., Petrou, K. & Kranz, S.A. 2011, 'Fluorescence as a Tool to Understand Changes in Photosynthetic Electron Flow Regulation' in Suggett, D.J., Borowitzka, M.A. & Prasil, O. (eds), Chlorophyll a Fluorescence in Aquatic Sciences : Methods and Applications, Springer, United Kingdom, pp. 75-89.View/Download from: UTS OPUS or Publisher's site
This chapter investigates the use of chlorophyll a fluorescence to better understand changes in the regulation of photosynthetic electron transport. It describes the different electron pathways utilised by photosynthetic organisms, including pathways used in photosynthesis as well as alternative electron cycling (AEC). The major photoprotective processes are described, in particular, non-photochemical quenching (NPQ) and its three components, energy-dependent quenching (qE), state-transition quenching (qT), and photoinhibition (qI). Fluorescence and NPQ responses to light stress are compared across a higher plant, diatom and cyanobacteria. Photosynthesis is a complex interaction of complementary processes making the identification and isolation of a particular photosynthetic pathway or process inherently difficult. Therefore, we describe the use of chemicals which allow for the differentiation of mechanistic photosynthetic processes, such as electron transport pathways, CO2 fixation and the use of trans-thylakoid proton gradients, which can be effectively understood and quantified using chlorophyll fluorescence detection techniques.
Chartrand, K.M., Rasheed, M., Petrou, K. & Ralph, P.J. 2012, 'Establishing tropical seagrass light requirements in a dynamic port environment', Proceedings of the 12th International Coral Reef Symposium, Cairns, Australia, 9-13 July 2012, International Coral Reef Symposium, ReefBase, Cairns.View/Download from: UTS OPUS
Tropical seagrasses inhabit naturally turbid waters with dynamic light environments and variable water quality in coastal waters adjacent to the Great Barrier Reef. Large tidal fluxes amplify the magnitude of these conditions with extreme high and low light over relatively short time scales (i.e. hours). Large port developments in the region have the potential to confound the complex relationships between seagrass physiology and this dynamic light field with the onset of dredging and their associated turbid plumes. Understanding the capacity for seagrasses to respond to changes in the quantity and quality of the light environment will allow for prediction of how seagrass species and populations will tolerate changes in light attenuation that may occur during dredging. We present a strategy for determining seasonal-specific light requirements for an intertidal tropical seagrass community in a port environment. Locally relevant light requirements are established by describing the relationships among photosynthetic inputs and losses, tidal exposure, shifts in spectral light quality, seasonality and the capacity to utilise below ground carbon reserves. The outcomes of the study provide guidelines for a mitigation strategy that is focused on maintaining critical windows of light to support seagrass growth and the longer term survival of these productive coastal ecosystems.
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.
Chartrand, K.M., McKenna, S.A., Petrou, K., Jimenez Denness, I.M., Franklin, J., Sankey, T.L., Hedge, S.A., Rasheed, M. & Ralph, P.J. DEEDI Publication 2010, Port Curtis Benthic Primary Producer Habitat Assessment and Health Studies Update: Interim Report December 2010, pp. 1-128, Cairns.View/Download from: UTS OPUS
Prof. Rafel Simo (Institut de Ciencies del Mar)
Dr Phil Heraud (Monash University)
Dr Andrew Davidson (Australian Antarctic Division)
Prof. Ruth Gates (University of Hawaii)
Dr Brook L Nunn (University of Washington)
Dr Scarlett Trimborn (Alfred Wegener Institute)
Dr Christel Hassler (University of Geneva)
Dr Sven Kranz (Florida State University)
Prof. John Beardall (Monash University)
Prof. Alexander Ruban (Queen Mary University London)
Dr Ester Garces (Institut de Ciencies del Mar)