My primary area of expertise is stable isotope analysis. Stable isotopes are naturally occurring alternative forms of elements like carbon and nitrogen, which are distinguished by their different molecular weights. They are an amazing tool that let us trace the flow of nutrients up the food chain, or track the migration of fish, birds, and insects across entire continents and oceans. Using isotopes, I have studied the habitat use and diet of sharks on the Great Barrier Reef, examined the effects of human pollution on prawns, and mapped the influence of climate on grass and shrub distribution across Australia. My other key research interests include species distribution modeling, animal tracking, and food webs. I am always open to collaboration and supervision on a wide assortment of topics. Below are brief summaries of some of my major research projects, past and present.
C3 and C4 distribution in Australia
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Understanding the environmental forces that drive plant distribution are critical to protecting our native ecosystems. Australia is an ecologically diverse country with a enormous range of climate conditions. In this project, I seek to understand the climate and soil conditions that control the distribution of warm-season (aka C4) and cool-season (aka C3) plants. My goal is to create Australia-wide spatial vegetation models that can predict the distribution of these species across the country and into the future. I also plan to build δ13C leaf isoscape, a map that predicts of carbon isotope ratios of plants at a continental scale. Isoscapes are incredibly useful tools when studying animal migration and diet.
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Deepwater shark diet revealed using isotope analysis
Dr Cassie Rigby hard at work near Swain Reefs, southern Great Barrier Reef Marine Park. She is holding an eastern spotted gummy shark, which lives at a depth of 400 metres. Photo by © Cassandra Rigby
Australia’s Great Barrier Reef is famous for its coral reef systems, but 1/3 of the reserve consists of largely unknown deep water habitat. These areas are increasingly being fished and deep dwelling sharks and rays are often caught as bycatch. In this project, we used stable isotope analysis to evaluate the diet, movement, and ecological interactions of deepwater sharks in Australian waters. We found that most deepwater sharks in our study had unique isoptice niches, indicating they eat different prey. We also found that shark size has a big influence on diet. This research would not be possible without the generous support of the Save Our Seas Foundation. Read more on my Save Our Seas Project Page
New tracer methods for revealing the hidden connections between ecosystems
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Marine and terrestrial ecosystems are connected by rivers, which carry nutrients, animals, and human pollutants across the land-sea boundary. In this project, we wanted to understand how land-based inputs effect coastal marine habitats. We analysed the concentrations of different metals, trace elements, and isotopes in nearshore prawns and used them as "bio-indicators" of pollution in a busy urban bay (Moreton Bay, Brisbane). We found prawns collected closer to shore had higher concentrations of certain metals and tracers, which tells us nearshore areas are more strongly affected by human activities, like agriculture and sewage. The good news is the concentrations of pollutants in prawns was low, so it does not appear to effect prawn condition and they are safe for human consumption.
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Most of us enjoy having prawns for dinner, but the chemical ‘fingerprints’ of these tasty critters can also tell us a lot about the health about coastal habitats!
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PhD Research: Shark movement and diet in a diverse coastal ecosystem
Different species have been found to exhibit generalist, opportunistically selective, and specialist resource use strategies. Sharks using these distinct strategies will have unique impacts on marine communities and respond differently to environmental fluctuation. I used a combination of passive acoustic telemetry and stable isotope analysis to determine the space use, habitat selection, and habitat specialization patterns of different shark populations on the GBR. By using two distinct techniques to study animal movement over large and small scales, l was able to better understand the foraging behaviours and distribution patterns of shark species.
Supervised Student Projects
Rachel Atkins (Honours, 2020) – “Carbon isotopic tools for determining the photosynthetic pathway of floral communities”, Department of Earth Sciences, University of Adelaide
Patrick Timmins (Honours, 2019) “Direct measurement of soil microplastic concentration using MIR spectroscopy”, School of Agriculture, Food, and Wine, University of Adelaide
Patrick Timmins (Honours, 2019) “Direct measurement of soil microplastic concentration using MIR spectroscopy”, School of Agriculture, Food, and Wine, University of Adelaide
