Coral bleaching and habitat degradation increase susceptibility to predation for coral-dwelling fishes

Abstract

Climate-induced coral bleaching frequently leads to declines in the abundance and diversity of coral-associated fishes, though the proximate causes of these declines are largely unknown. In this study, we show that coral-dwelling damselfishes associated with bleached and dead coral hosts are more susceptible to predation compared with fishes associated with healthy coral colonies. Although the predator (Pseudochromis fuscus) actively avoided both bleached and recently dead corals, they were almost twice as likely to strike at prey associated with the stark white colonies of bleached corals. These results suggest that coral-dwelling fishes are much more conspicuous against the bleached-white background, increasing their susceptibility to predation. Direct estimates of predation rates in aquaria were 33% and 37% on bleached and recently dead coral colonies, respectively, compared with 25% on healthy coral colonies. However, predation rates were highest (42%) on algal-covered corals, reflective of colonies that have further degraded after bleaching. We argue that increased susceptibility to predation may contribute to declines in abundance of coral-dwelling fishes after host coral bleaching. Even if predation does not cause increased in situ mortality, it is likely that increased exposure to predators will provide significant motivation for coral-dwelling fishes to vacate bleached coral hosts.