Trophic plasticity in an obligate corallivorous butterflyfish

Changes in the abundance and/or taxonomic composition of corals are having direct impacts on the structure of reef fish assemblages, with those species that rely directly on live coral for food or shelter being most affected. Despite this, many specialist coral feeders persist on reefs where preferred coral taxa are rare. We examined feeding selectivity of the obligate corallivorous butterflyfish Chaetodon octofasciatus, a species known to feed predominantly on Acropora spp. corals, between a heavily urbanized coral reef system (Singapore) with low Acropora spp. cover, and a relatively intact reef system containing high Acropora spp. cover (Pulau Tioman, eastern Peninsular Malaysia). Both reef systems supported similar densities of C. octofasciatus, with live coral dominating the diet in both locations. In Pulau Tioman, C. octofasciatus fed on 14 genera, (27.45% of available coral genera), with over a third of bites on Acropora spp. In contrast, C. octofasciatus on Singaporean reefs fed on 26 genera (45% of available coral genera), with only 4% of bites on Acropora spp. Despite specialist corallivores being viewed as highly susceptible to reductions in their preferred dietary coral taxa, this research highlights the potential importance of diet plasticity in sustaining populations.