Climate change and habitat fragmentation in coral reef ecosystems

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One of the most striking impacts of human development is the replacement of natural wildlife habitat with either agriculture or urban environments. Not only does such development reduce the overall availability of wildlife habitat, it often fragments the landscape so that habitat patches become smaller and increasingly isolated. This so called 'habitat fragmentation' causes many problems for wildlife including reducing biodiversity and the value of ecosystem services. Not surprisingly, habitat fragmentation has become one of the most intensively-studied phenomena in terrestrial ecology, underpinning the fields of landscape ecology and population biology. Despite the existence of major disturbance phenomena in marine ecosystems, the effects of habitat fragmentation in marine systems have barely been considered. There are several reasons for this including difficulties in mapping habitats underwater, limited availability of ecosystem models, and difficulty in establishing the connectivities among populations through larval dispersal. Although the lack of study of habitat fragmentation in marine ecosystems is understandable, the potential importance of this process sits high on the conservation agenda, primarily because of the impacts of climate change. In 1998, for example, unusually high sea temperatures in tropical regions led to unprecedented mortality of reef corals with many reefs losing 99% of their living coral and an estimated 25% of the world's reefs losing their coral dominance within a few months. With the recent emergence of models of ecosystem dynamics and larval connectivity among coral reefs, the constraints to studying fragmentation in marine systems have recently been lifted. The research team is multi-disciplinary and provides the four key ingredients needed to study climate change impacts on marine habitats. These are (1) mapping of the existing distribution of reef habitat with satellite imagery (PI, Peter Mumby an ecologist), (2) modelling the ecological dynamics within patches of reef (Mumby), (3) spatially-realistic model of the dispersal of larvae among patches of reef (Project Partner, Claire Paris a biological oceanographer), and (4) access to and use of global climate models (Co-I, Peter Cox, Met Office Professor of Climate Dynamics at the University of Exeter). The model will be used to ask fundamentally-important questions about climate change and opportunities for human mitigation and adaption. First we recognize that the Earth is already locked into a degree of warming even if urgent action was taken to reduce greenhouse gas emissions. We examine the consequences of these inevitable impacts on reefs, even if we were to take appropriate local conservation (i.e., providing a 'best-case' scenario of expected change). We then evaluate the impact of international action to reduce greenhouse gas emissions by simulating how each emission scenario effects reefs through the processes of rising hurricane intensity, coral bleaching, and ocean acidification. Of course, most conservation action is taken at local scales so we also quantify the extent to which taking appropriate local action, such as preventing overexploitation of herbivorous fishes, influences the future trajectories of reef habitat loss and fragmentation. For example, to what extent does local action buy time for reefs to adapt? The net impacts of ocean acidification are poorly understood so we will carry out a preliminary sensitivity analysis of reefs to at least one putative impact of acidification (reduced coral growth rate). Lastly, we undertake field studies to test the predictions of the model by simulating the actual disturbance histories of reefs since 1950 and comparing the predicted patterns of reef health to those found in the field. If the grant is funded by NERC, the University of Exeter has committed to fund an inter-disciplinary PhD studentship to extend the analyses over a continuous range of emission scenarios