Effects of multiple environmental stressors on reef corals

Predictions suggest that coral reefs will soon fall victim to the changes in environmental conditions associated with climate change such as rising seawater temperatures, ocean acidification and anthropogenic nutrient enrichment of coastal reefs ((Hoegh-Guldberg et al., 2007)

All of these stressors affect coral growth and calcification. However, recent research of the supervisory team has shown that a much more detailed view of the effect of these major environmental stressors is required, in particular when they act in combination. These recent findings show, for instance, that it is actually a temporary nutrient starvation resulting from skewed nutrient ratios or eutrophication that renders coral more susceptible to heat stress, and not necessarily the nutrient enrichment per se (D’Angelo & Wiedenmann, 2014, Rosset et al., 2017).

This project will determine in controlled laboratory experiments how the combination of environmental stressors (low pH / high temperature / nutrient availability) affects coral growth and how these effects are reflected in the structure and composition of the coral skeletons. Analyzing these proxies in archived coral skeleton material from localities with contrasting environmental conditions from different parts of the world, the project will establish the contribution of individual stress factors affecting coral reefs from the recent past to present.

Replicate colonies of established laboratory strains of different coral species will be used as models. The corals will be cultured in separate compartments of the experimental mesocosm at the National Oceanography Centre, Southampton. The unique capacity of the experimental systems will allow for the exposure to different nutrient regimes, pH and temperature. Carbonate chemistry will be modified by bubbling CO2 in experimental compartments. Environmental parameters will be monitored daily in the culture systems.

Coral growth and net calcification rate will be measured by buoyant weight analysis and measurements of linear extension of corals with branching and digitate morphology. The porosity of the coral skeletons will be examined using X-Ray micro-computed tomography (Micro-CT) in the Biomedical Imaging Unit at the University of Southampton.

The project will make use of the analytical facilities at the University of Southampton to determine C, Ca, nitrogen (N), phosphate (P), and N:P ratios to calibrate the effects of changes in temperature and pH under different nutrient environments on the skeletal composition.

Coral material originating from different regions and collected at distinct times, available at the Natural History Museum in London, will be analysed using the protocols optimised from the experiments performed under controlled conditions.

The SPITFIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted at Ocean and Earth Science, National Oceanography Centre Southampton.

The student will perform an interdisciplinary research project. The training will involve a broad spectrum of methods ranging from the aquaculture of reef corals and physiological experiments performed under tightly controlled laboratory conditions to elemental composition, structure and imaging analysis of skeletal samples. The student will be encouraged to contribute own ideas to shape the course of the project. The skills acquired during this project represent also key-qualifications for careers in other fields of academic and industry research.