Fish predation on corals promotes the dispersal of coral symbionts

Abstract

Predators drive top-down effects that shape prey communities, but the role of predators in dispersing prey microbiomes is rarely examined. We tested whether coral-eating (corallivorous) fish disperse the single-celled dinoflagellate symbionts (family Symbiodiniaceae) of their prey. Our findings demonstrate that: (1) coral-eating fish egest feces containing live Symbiodiniaceae at densities up to seven orders of magnitude higher than other environmental reservoirs such as sediments and water; (2) Symbiodiniaceae communities in the feces of most corallivores are compositionally similar to those in corals; (3) some obligate corallivore species release over 100 million Symbiodiniaceae cells per 100 m2 per day; and (4) after being egested, corallivore feces often come in direct contact with coral colonies (potential hosts for Symbiodiniaceae). These findings suggest that fish predators can play an important role in symbiont acquisition by corals; such predators may have a previously unrecognized, indirect positive effect on prey health.