A balancing act in coral reefs: how stoichiometry creates resilience in tropical reef systems

Biogeochemical Cycles



Coral reefs are one of the most biodiverse ecosystems on Earth. The ecosystem services they provide, including coastal protection, tourism, food security and medical derivatives, are valued at over $100 billion annually. However, around the world coral reefs are facing increasing pressure from direct human activities such as coastal development and pollution, as well as rapidly altering environmental conditions as a result of climate change. These pressures can cause degradation of coral cover, proliferation of algal growth and ultimately a complete ecosystem shift and loss of the reef habitat. Physiological resilience to these pressures, at the organism to community scale, is crucial for the future survival of coral reefs.

Paradoxically, despite being highly productive and supporting diverse marine ecosystems, coral reefs thrive in low-nutrient environments thanks to efficient nutrient recycling and retention. How they maintain the ratio between the basic elements of life (e.g. carbon, nitrogen, calcium) may therefore be fundamental to how coral reefs respond to environmental change. This so-called “ecological stoichiometry” has a long history of research within the open ocean, but the cycling of nutrients and balance of elements within coral reef systems remains largely unknown. Recent work by the supervisory team suggests that corals, and other calcifying organisms, can exhibit a wide range in C:N ratios, suggesting that the stoichiometry of a coral reef system may be highly dynamic in response to environmental change.

The aim of this project is to quantify the variability of elemental stoichiometry within the coral reef system and to identify the environmental drivers controlling this variability. Given their uncertain future, this information will provide a foundation for predicting coral reef resilience, and place these ecosystems within the wider context of global biogeochemical cycling.

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Image Captions

Picture5.jpg: How does this bounty of marine life impact the cycling of the basic elements needed for life on the planet? [credit: Philip Hamilton / Coral Reef Image Bank

Picture2.png: Coral and algal sampling on a coral reef by one of the project supervisors [credit: Nick Kamenos]


The PhD student will have the opportunity to collect coral reef and water samples from multiple sites within the Caribbean (SCUBA diving is optional) for stoichiometric analysis. Sampling surveys will be conducted at the organism to community scale and combined with advanced ecological survey techniques (e.g. 3D habitat modelling) and historical biodiversity data to enable a mechanistic understanding of stoichiometric dynamics within the reef. This could be conducted in the laboratory should Covid-19 travel restrictions still be in place; physical distancing in the field and off-peak visits will also be possible. Innovative mass spectrometry technologies available at the Lyell Centre will also enable stoichiometric partitioning at the organism-level, e.g. between lipids and carbohydrates. Further mechanistic insight will be gained via the opportunity to conduct multifactorial laboratory aquarium experiments under highly controlled conditions of light, temperature, nutrients and carbon chemistry, using state-of-the-art facilities available within the Lyell Centre.

Project Timeline

Year 1

Literature review, field & analytical technique development, summer fieldwork

Year 2

Sample analysis & interpretation, laboratory experiments, summer fieldwork, presentation at a national conference

Year 3

Sample analysis & interpretation, write-up for publication, presentation at an international conference

Year 3.5

Writing-up of results and completion of thesis, submission of papers for publication

& Skills

Project support

The facilities, equipment and expertise available within the institutions and supervisory team provide a combination of world-leading field, analytical and laboratory capability and technical support that ideally fits this PhD project, maximising the expert training that will be available.

This project will equip the student with a range of skills, including fieldwork, analytical science, numeracy and translation of science for wider audiences. Specific research skills will include:
– Elemental and water chemistry analysis
– Coastal marine fieldwork
– Invertebrate and algal culturing and husbandry
– Experimental design
– Environmental statistics

PhD support

The Lyell Centre has a large research student cohort that will provide peer-support throughout the studentship, including participation in the annual post-graduate research conference. All project supervisors are also highly research-active. This PhD student will interact with all members of their research groups through lab-group meetings at the Lyell Centre, University of Glasgow and Operation Wallacea, providing an opportunity to learn about other techniques and research areas which may be applicable to their research. Additionally, the supervisors are all based in research-active departments that span a broad range of ecological, environmental and geoscience research, exposing the scholar to a range of other research areas. Active participation in these research groups will provide the opportunity to discuss cutting-edge topics in the field, review recent papers and to present current research plans to academics with a common research interest in an informal and supportive atmosphere. The PhD student will also have the opportunity to undertake a placement with Operation Wallacea, providing work experience within a non-academic organisation.

Where required, and to maintain continued professional development, the scholar will be supported to attend specialist courses directly aligned to the project, for example:
– Elemental analysis via mass spectrometry and sample partitioning via selective extraction protocols.
– Field first aid course in the first 6 months of the project.
– Potentially, scientific diving courses
– Analytical training provided by the supervisors and / or specialist technicians for each piece of instrumentation required for analyses.
– Attendance to transferable skills training such as data management, scientific writing and science communication. These are provided for free within Heriot-Watt University’s Research Futures Academy.

References & further reading

Sterner, R.W., 2015. Ocean stoichiometry, global carbon, and climate. Proceedings of the National Academy of Sciences, 112(27), pp.8162-8163.

Moreno, A. R., & Martiny, A. C. (2018). Ecological stoichiometry of ocean plankton. Annual review of marine science, 10, 43-69.

Elser, J. J. (2000). Ecological stoichiometry: from sea to lake to land. Trends in Ecology & Evolution, 15(10), 393-394.

Further Information

In the first instance, enquiries should be directed to the primary supervisor, Dr Heidi Burdett (h.burdett@hw.ac.uk). Please indicate why you are interested in this project and attach your CV to the email.

For eligible candidates, funding is available to cover tuition fees, stipend and research costs. However, please note that this project is in competition with others for funding, and success will depend on the quality of applications received.

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