Dietary resilience of coral reef fishes to habitat degradation

The ability of consumers to adjust their diet in response to resource shifts is a key mechanism allowing the persistence of populations and the underlying species’ adaptive capacity. Yet on coral reefs, one of the marine habitats most vulnerable to global change, the extent to which species alter their diet remains poorly understood. Here, we integrated DNA-based gut content analyses (metabarcoding), otolith analysis, body condition, and field surveys to test how dietary versatility can mediate effects of habitat degradation on two invertivorous fishes: Chaetodon capistratus, a browser, and Hypoplectrus puella, an active predator. Metabarcoding revealed significant dietary variation in both species across reefs with different levels of coral cover. However, the response was more pronounced in the browser, whose diet was anthozoan-dominated on healthy reefs, whereas annelid-dominated on degraded reefs. We found slower growth and reduced body condition on degraded reefs in the browser but not the active predator. Our results suggest that while dietary versatility serves as a mechanism to cope with degraded environments, the degree to which dietary shifts can buffer from the effects of habitat degradation varies between species. Finally, we detected intraspecific dietary variation across sites that suggests food webs and energy flow differ at relatively small scales between healthy and degraded reefs.