Consumer feces impact coral health in guild-specific ways

Abstract

Microbiota from consumer feces can impact resource species in guild-specific ways. We tested the effect of fresh and heat-killed feces from corallivorous (coral-eating) and grazer/detritivorous fish on coral health and found that fresh grazer/detritivore feces, but not fresh corallivore feces, affected coral health in detrimental ways compared to heat-killed feces, suggesting that microbiota in grazer/detritivore feces were harmful. Bacterial diversity across 10 fish species suggests our experimental findings are generalizable to consumer guild: corallivore feces contained more coral-associated bacteria, and lower abundances of the coral pathogen, Vibrio coralliilyticus. These findings recontextualize the ecological roles of consumers on coral reefs: although herbivores support coral dominance through removal of algal competitors, they also disperse coral pathogens. Corallivore predation can wound corals, yet their feces contain potentially beneficial coral- associated bacteria, supporting the hypothesized role of corallivores in coral symbiont dispersal. Such consumer-mediated microbial dispersal as demonstrated here has broad implications for environmental management.