A balancing act? Elemental stoichiometry in coral reefs of the Anthropocene

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. Fundamental to how coral reefs respond to environmental change is ecological stoichiometry – how they maintain the ratio between the basic elements of life (e.g. carbon, nitrogen, calcium) required for growth and survival. Ecological stoichiometry has a long history, rooted in part by our understanding of how marine plankton control the global cycling of carbon (C), nitrogen (N) and phosphorus (P). We are now learning that rather than occurring at fixed ratios, the cycling and use of these elements shows important plasticity across organisms and ecosystems, with the sum of parts being more influential than individual species or processes. However, 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 more dynamic than previously assumed. These initial insights need to be expanded and placed in the wider context of coral reef ecology and nutrient cycling, answering fundamental questions about what the natural elemental balance is in coral reefs, how coral reefs respond to carbon or nutrient enrichment, how light and prey availability affects the balance between autotrophy and heterotrophy and how coral reefs impact wider nutrient cycling in the oceans.

Project aim: This project will quantify the stoichiometric variability associated with coral reef habitats and identify how this responds to environmental and ecological pressures. This is important as it will transform our understanding of the role of coral reef systems in global biogeochemical cycles, and their resilience to human and environmental pressures.

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Image Captions

Picture1.png: “Coral and algal sampling on a coral reef by one of the project supervisors. Image credit: Nick Kamenos.”
CoralReefImageBank.jpg: “How does this bounty of marine life impact the cycling of the basic elements needed for life on the planet? Image credit: Umeed Mistry / Coral Reef Image Bank.”


The scholar will have the opportunity to collect coral reef and water samples from multiple sites within the Caribbean (SCUBA diving is optional) for elemental analysis. This will be conducted at the organism to community scale and combined with advanced ecological survey techniques to enable a mechanistic understanding of stoichiometric dynamics within the reef. Innovative mass spectrometry technologies available to the scholar 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 and set-up of controlled laboratory experiments for preliminary work and sample collection, preparation of literature review for publication

Year 2

Further laboratory experiments (e.g. feeding experiments), concurrent sample analysis & interpretation, summer fieldwork, presentation at a national conference and publication preparation on initial results

Year 3

Final laboratory experiments, concurrent 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 final 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 aquarium 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

Scholar support: The Lyell Centre, Heriot-Watt University has a large research student cohort that will provide peer-support throughout the studentship. The scholar will participate in the annual post-graduate research conference within the School of Energy, Geoscience, Infrastructure and Society (EGIS), providing an opportunity to present their research to postgraduates and staff within the School, and to also learn about the research conducted by their peers. All project supervisors are highly research-active: the scholar 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. Via CASE-partnership, the scholar will also have the opportunity to undertake a 3-month placement with Operation Wallacea, providing work experience within a non-academic organisation.

Where required, and to maintain continued professional development, the scholar will be encouraged to attend specialist courses directly aligned to the project:
• Elemental analysis via mass spectrometry and sample partitioning via selective extraction protocols.
• This project will involve some fieldwork, thus the scholar may attend a field first aid course in the first 6 months of the project.
• If desired, the scholar may attend diving orientated courses
• Analytical training will be provided by the supervisors and / or specialist technicians for each piece of instrumentation required for analyses.
• The project supervisors will also support and encourage the scholar’s attendance on transferable skills training such as data management, scientific writing and science communication. These are provided for free by Heriot-Watt University.

References & further reading

Moreno, A.R. and Martiny, A.C., 2018. Ecological stoichiometry of ocean plankton. Annual review of marine science, 10, pp.43-69.
Lovelock, C.E., Reef, R. and Pandolfi, J.M., 2014. Variation in elemental stoichiometry and RNA: DNA in four phyla of benthic organisms from coral reefs. Functional ecology, 28(5), pp.1299-1309.
Sterner, R. W., and Elser, J. J. (2002). Ecological Stoichiometry: The Biology of Elements from Molecules to the Biosphere. Princeton, NJ: Princeton University Press.Van de Waal, D.B., Elser, J.J., Martiny, A., Sterner, R.W. and Cotner, J., 2018. Progress in ecological stoichiometry. Frontiers in microbiology, 9, p.1957.

Further Information

In the first instance, enquiries should be directed to the Lyell supervisory team: Drs Alex Poulton (a.poulton@hw.ac.uk) and 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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