I am a marine biologist in the Future Reefs Group with research interests including: the impact of climate change on coral reefs, photophysiology of marine organisms (e.g. corals and phytoplankton) and using active Chlorophyll-a fluorometry to estimate phytoplankton primary productivity.
My current research project is to understand how climate-change driven loss of oxygen from the oceans is impacting coral reef ecosystems. I work in a team team studying how corals on the Great Barrier Reef respond to hypoxic (low oxygen) conditions, to determine the oxygen concentration at which corals experience physiological stress. Understanding how such hypoxia thresholds vary for key coral species and how these are modified by other stressors (e.g. ocean warming and acidification) will help us better understand how future reef systems will respond to ongoing ocean deoxygenation.
My other main research focus is the application of active fluorometry and other bio-optical tools to assess health and productivity of photosynthetic marine organisms such as corals and algae. This follows on from research conducted during my PhD (Biogical Oceanography) where i examined taxonomic and environmental factors which regulate phytoplankton photosynthetic efficiency in Australian waters.
Alongside my research, I also oversee the day-to-day running of our coral aquarium facility within the C3 Climate Change Cluster. Here, our team of researchers and volunteers grow and propogate tropical corals for use in a range of research projects examining how climate change impacts coral reefs. This directly minimises our research "footprint" on the reef itself and gives our students and researchers direct access to a range of hard and soft coral species for use in aquarium-based experiments.
I have ~5 years experience in tropical aquaculture, having worked for Tropical Marine Centre (UK), and several other commercial aquarium facilities in the following areas:
- Captive propagation of hard and soft corals.
- Aquaculture of high-value ornamental bivalves (Tridacnid clams).
- Animal husbandry (corals, invertebrates, fish, exotics such as sharks and rays).
- Commercial-scale captive breeding (tropical)
- Design and setting-up of aquarium systems (public display, commercial and research)
Can supervise: YES
- Ocean deoxygenation and how this impacts coral reefs.
- Using bio-optical tools (e.g. Fast Repetition Rate fluorometry, FRRf) to measure photosynthetic rates and photophysiology of marine organisms.
- Environmental control of photosynthesis and productivity of photosynthetic marine organisms (e.g. how light, temperature and nutrient availability regulate the electron requirement for carbon fixation).
- Aquaculture and captive-propagation of reef building corals, marine and freshwater fish species and bivalves such as giant clams.
- Predicting and modelling primary production from bio-optical assessments to understand atmospheric CO2 drawdown and implications for global climate.
Varkey, D, Mazard, S, Jeffries, T, Hughes, D, Seymour, J, Paulsen, IT & Ostrowski, M 2018, 'Stormwater influences phytoplankton assemblages within the diverse, but impacted Sydney Harbour estuary', PLoS ONE, vol. 13, no. 12, pp. e0209857-e0209857.View/Download from: UTS OPUS or Publisher's site
Sydney Harbour is subjected to persistent stress associated with anthropogenic activity and global climate change, but is particularly subjected to pulse stress events associated with stormwater input during episodic periods of high rainfall. Photosynthetic microbes underpin metazoan diversity within estuarine systems and are therefore important bioindicators of ecosystem health; yet how stormwater input affects their occurrence and distribution in Sydney Harbour remains poorly understood. We utilised molecular tools (16S/18S rRNA and petB genes) to examine how the phytoplankton community structure (both prokaryotes and eukaryotes) within Sydney Harbour varies between high and low rainfall periods. The relative proportion of phytoplankton sequences was more abundant during the high rainfall period, comprising mainly of diatoms, an important functional group supporting increased productivity within estuarine systems, together with cyanobacteria. Increased spatial variability in the phytoplankton community composition was observed, potentially driven by the steepened physico-chemical gradients associated with stormwater inflow. Conversely, during a low rainfall period, the proportion of planktonic photosynthetic microbes was significantly lower and the persistent phytoplankton were predominantly represented by chlorophyte and dinoflagellate sequences, with lower overall diversity. Differences in phytoplankton composition between the high and low rainfall periods were correlated with temperature, salinity, total nitrogen and silicate. These results suggest that increased frequency of high-rainfall events may change the composition, productivity and health of the estuary. Our study begins to populate the knowledge gap in the phytoplankton community structure and substantial changes associated with transient environmental perturbations, an essential step towards unravelling the dynamics of primary production in a highly urbanised estuarine ecosystem in response to cli...
Hughes, DJ, Varkey, D, Doblin, MA, Ingleton, T, Mcinnes, A, Ralph, PJ, van Dongen-Vogels, V & Suggett, DJ 2018, 'Impact of nitrogen availability upon the electron requirement for carbon fixation in Australian coastal phytoplankton communities', Limnology and Oceanography, vol. 63, no. 5, pp. 1891-1910.View/Download from: UTS OPUS or Publisher's site
© 2018 Association for the Sciences of Limnology and Oceanography Nitrogen (N) availability affects phytoplankton photosynthetic performance and regulates marine primary production (MPP) across the global coast and oceans. Bio-optical tools including Fast Repetition Rate fluorometry (FRRf) are particularly well suited to examine MPP variability in coastal regions subjected to dynamic spatio-temporal fluctuations in nutrient availability. FRRf determines photosynthesis as an electron transport rate through Photosystem II (ETRPSII), requiring knowledge of an additional parameter, the electron requirement for carbon fixation (KC), to retrieve rates of CO2-fixation. KC strongly depends upon environmental conditions regulating photosynthesis, yet the importance of N-availability to this parameter has not been examined. Here, we use nutrient bioassays to isolate how N (relative to other macronutrients P, Si) regulates KC of phytoplankton communities from the Australian coast during summer, when N-availability is often highly variable. KC consistently responded to N-amendment, exhibiting up to a threefold reduction and hence an apparent increase in the efficiency with which electrons were used to drive C-fixation. However, the process driving this consistent reduction was dependent upon initial conditions. When diatoms dominated assemblages and N was undetectable (e.g., post bloom), KC decreased predominantly via a physiological adjustment of the existing community to N-amendment. Conversely, for mixed assemblages, N-addition achieved a similar reduction in KC through a change in community structure toward diatom domination. We generate new understanding and parameterization of KC that is particularly critical to advance how FRRf can be applied to examine C-uptake throughout the global ocean where nitrogen availability is highly variable and thus frequently limits primary productivity.
Hughes, DJ, Campbell, DA, Doblin, MA, Kromkamp, JC, Lawrenz, E, Moore, CM, Oxborough, K, Prášil, O, Ralph, PJ, Alvarez, MF & Suggett, DJ 2018, 'Roadmaps and Detours: Active Chlorophyll- a Assessments of Primary Productivity Across Marine and Freshwater Systems.', Environmental science & technology, vol. 52, pp. 12039-12054.View/Download from: UTS OPUS or Publisher's site
Assessing phytoplankton productivity over space and time remains a core goal for oceanographers and limnologists. Fast Repetition Rate fluorometry (FRRf) provides a potential means to realize this goal with unprecedented resolution and scale yet has not become the "go-to" method despite high expectations. A major obstacle is difficulty converting electron transfer rates to equivalent rates of C-fixation most relevant for studies of biogeochemical C-fluxes. Such difficulty stems from methodological inconsistencies and our limited understanding of how the electron requirement for C-fixation (Φe,C) is influenced by the environment and by differences in the composition and physiology of phytoplankton assemblages. We outline a "roadmap" for limiting methodological bias and to develop a more mechanistic understanding of the ecophysiology underlying Φe,C. We 1) re-evaluate core physiological processes governing how microalgae invest photosynthetic electron transport-derived energy and reductant into stored carbon versus alternative sinks. Then, we 2) outline steps to facilitate broader uptake and exploitation of FRRf, which could transform our knowledge of aquatic primary productivity. We argue it is time to 3) revise our historic methodological focus on carbon as the currency of choice, to 4) better appreciate that electron transport fundamentally drives ecosystem biogeochemistry, modulates cell-to-cell interactions, and ultimately modifies community biomass and structure.