Size and wave exposure shape parrotfish distributions and function in shallow coral reefs

Abstract

Abstract Wave exposure is a powerful environmental filter in shallow coral reefs, influencing species distributions and mediating patterns of decline and recovery. How mobile species navigate wave regimes is often mediated by size, morphology and swimming behaviour. How species navigate turbulent wave regimes is especially important in the case of functionally important groups like parrotfish. We explored how wave exposure shapes the distribution, biomass and bioerosional role of parrotfish assemblages in coral reefs using in-water visual surveys in the Lakshadweep Archipelago. Despite being relatively fusiform, we found that parrotfish distribution was strongly influenced by wave exposure, mediated by individual size and body shape. There was a clear decoupling between density, biomass and bioerosion in relation to wave regimes. Parrotfish density was highest in shallow exposed sites, dominated by large shoals of small individuals with low body depth ratios. In contrast, biomass was highest in deeper locations, where larger individuals were most abundant. This differential filtering of species and sizes resulted in considerable heterogeneity in the spatial distribution of bioerosional processes on the reef. Our study highlights the importance of size and shape as critical traits in influencing community assembly and determining the distribution of function in parrotfish.