Habitat choice, recruitment and the response of coral reef Wshes to coral degradation

The global degradation of coral reefs is having profound eVects on the structure and species richness of associated reef Wsh assemblages. Historically, variation in the composition of Wsh communities has largely been attributed to factors aVecting settlement of reef Wsh larvae. However, the mechanisms that determine how Wsh settlers respond to diVerent stages of coral stress and the extent of coral loss on Wsh settlement are poorly understood. Here, we examined the eVects of habitat degradation on Wsh settlement using a two-stage experimental approach. First, we employed laboratory choice experiments to test how settlers responded to early and terminal stages of coral degradation. We then quantiWed the settlement response of the whole reef Wsh assemblage in a Weld perturbation experiment. The laboratory choice experiments tested how juveniles from nine common Indo-PaciWc Wshes chose among live colonies, partially degraded colonies, and dead colonies with recent algal growth. Many species did not distinguish between live and partially degraded colonies, suggesting settlement patterns are resilient to the early stages of declining coral health. Several species preferred live or degraded corals, and none preferred to associate with dead, algal-covered colonies. In the Weld experiment, Wsh recruitment to coral colonies was monitored before and after the introduction of a coral predator (the crown-of-thorns starWsh) and compared with undisturbed control colonies. StarWsh reduced live coral cover by 95–100%, causing persistent negative eVects on the recruitment of coral-associated Wshes. Rapid reductions in new recruit abundance, greater numbers of unoccupied colonies and a shift in the recruit community structure from one dominated by coral-associated Wshes before degradation to one predominantly composed of algal-associated Wsh species were observed. Our results suggest that while resistant to coral stress, coral death alters the process of replenishment of coral reef Wsh communities.