Functional ecology of fish on coral reefs: the roles of seascape and subsistence fishing

Abstract

Globally, fish are being removed from our oceans at unsustainable rates. This is particularly true for coral reef fish, which, in addition to overfishing, are also under threat from global warming, ocean acidification, and pollution. Current conservation strategies for coral reef fisheries either indirectly control the amount of fish caught through restrictions on fishing effort, techniques, and areas, or directly limit fish catch using quotas for each fishery. However, to ensure that these conservation strategies function to their utmost potential, we need to identify the fishing techniques and seascape characteristics that have the most impact on coral reefs and their associated fish assemblages. This thesis used a field study on a group of remote Pacific atolls to establish how fishing using traditional techniques for food, not profit (subsistence fishing) affected coral reef fish assemblages. I demonstrate that subsistence fishing may be an effective way of providing food for small island communities, while also maintaining pristine reef fish assemblages. This thesis also investigated how connections in coastal seascapes affected crucial ecosystem functions on coral reefs. I show that connectivity can exert opposing effects on ecosystem functions, and that the distribution of fish and the ecosystem functions they provide may not align. I advocate that if marine spatial plans aim to incorporate ecosystem functions into their framework, they need to explicitly measure ecosystem function, rather than using proxies such as fish abundance. Finally, this thesis reports how the arrangement of mangroves and coral reefs in coastal seascapes varied globally, and how these differences affected the distribution of fish. I show that the configuration of coastal mangrove and coral reef seascapes, and their effects on fish, are correlated with tidal range, and I suggest that we cannot make global generalisations about the scale at which mangrove connections modify fish assemblages on coral reefs. This thesis makes direct recommendations on how to improve the conservation of coral reef fish. By endorsing low-impact fishing techniques and improving our understanding of seascape ecology, we can expect to improve conservation strategies for coral reefs, making them as practical and effective as possible.