Coral-dwelling fishes resistant to bleaching but not to mortality of host corals

Abstract

Coral bleaching is becoming an increasingly common disturbance on coral reefs, and although corals can remain bleached for months prior to recovery or death, little is known about how bleaching affects the associated fish community. The present study reports on recruitment and persistence of coral-dwelling fishes during a natural coral bleaching event in Kimbe Bay, Papua New Guinea. Transect surveys revealed that up to 80% of branching coral habitats were affected by bleaching. Healthy (i.e. unbleached), severely bleached, and dying colonies of corymbose Acropora spp. were tagged along the reef crest, and resident fish communities were monitored over time. There was no difference in the number of Pomacentrus moluccensis that settled on healthy versus bleached corals. Furthermore, the mean number of P. moluccensis recruits remaining on healthy and bleached corals did not differ after 4 wk. In contrast, the number of recruits remaining on dead colonies was lower after 4 wk and the frequency of recruit retention was significantly lower on dead colonies compared to healthy or bleached colonies. Similarly, the abundance of coral-dwelling gobies living on healthy or bleached corals did not decrease significantly over 8 wk, but all gobies disappeared from corals that died from bleaching. These results suggest that P. moluccensis recruits do not avoid bleached corals at settlement and that subsequent survival and/or movement of both recruits and adult coral-dwelling gobies is not negatively influenced, provided that the host coral remains alive. However, it is clear that if corals die from bleaching, coral-specialised fishes will quickly disappear, even prior to structural erosion of the habitat.