Biogeography versus resource management: how do they compare when prioritizing the management of coral reef fish in the south‐western Indian Ocean?

Abstract

AbstractAimNumbers of coral reef species are broadly influenced by historical, physical and geographical factors that are often the basis for prioritizing conservation and management investments. In contrast, the number of species at a site is often influenced by site‐specific factors, including abundance, benthic cover and other habitat features (depth and exposure), fishing pressure and resource management. Conservation policies and programmes often prioritize geographies or specific management systems within specific geographies. I evaluate the variance in number of species at the site scale and estimate the contributions of fishing pressure, local habitat factors and regional geography to local diversity.LocationCoral reefs of the south‐western Indian Ocean (SWIO).MethodsSite‐level species richness data from an extensive field sample of common coral reef fish at 266 sites in seven SWIO countries were analysed to create four species richness metrics to evaluate the effects of local site, geography and management.ResultsThe local number of species was strongly predicted by an asymptotic relationship with fish biomass, followed by habitat variables, and lastly by the geographical positions of latitude and longitude. A species richness centre or ‘hotspot’ was found between Madagascar and the African coastline, but the variance attributable to geography when biomass and habitat effects were removed was small. Evaluation of the number of species in five existing fisheries management categories indicated that differences were chiefly influenced by biomass rather than habitat factors.Main conclusionsAlthough the centre of species richness may indicate a climate refugium that should be considered in conservation prioritization, this diversity‐centre effect can weaken if habitat and biomass features are reduced by climate disturbances and fishing. Consequently, the highest priority for conserving local numbers of reef fish species is to maintain biomass above the c. 600 kg ha−1 threshold found in this study.