Ecological versatility and the decline of coral feeding fishes following climate driven coral mortality

Coral reefs are under threat due to climate-mediated coral mortality, which affects some reef coral genera more severely than others. The impact this has on coral reef fish is receiving increasing attention, with one focal area assessing impacts on fish that feed directly on live coral. It appears that the more specialised a species of corallivore, the more susceptible it is to coral declines. However data are sparse for the Indian Ocean, and little is known about why some corals are preferentially fed upon over others. Here I assess feeding specialisation in three species of coral feeding butterflyfish in the Chagos Archipelago, central Indian Ocean, assess the food quality of the coral genera they target and document patterns of decline in the Seychelles following a severe coral mortality event. Cheatodon trifascialis was the most specialised coral feeder, preferentially selecting for Acropora corals, however, when Acropora was scarce, individuals showed considerable feeding plasticity, particularly for the dominant Pocillopora corals. C. trifasciatus also preferentially fed on Acropora corals, but fed on a much more diverse suite of corals and also displayed some selectivity for Porites. C. auriga is a facultative corallivore and consumed ∼55% live coral, which lies within the wide range of coral dependence reported for this species. C:N ratio analysis indicated Lobophyllia and Acropora have the highest food quality, with Pocillopora having the lowest, which conforms with diet selection of corallivores and helps explain preferential feeding. Obligate specialist feeders displayed the greatest declines through coral mortality in the Seychelles with obligate generalists also declining substantially, but facultative feeders showing little change. Clearly a greater understanding of the species most vulnerable to disturbance, their habitat requirements and the functional roles they play will greatly assist biodiversity conservation in a changing climate.