# Dietary resilience of coral reef fishes to habitat degradation

## TL;DR

This study shows how two types of reef fish adjust their diets when coral reefs degrade, and how these changes affect their health differently.

## Contribution

The study reveals species-specific dietary and body condition responses to habitat degradation in reef fishes.

## Key findings

- Butterflyfish diets shifted from coral to worms on degraded reefs, with more variable body condition.
- Hamlet body condition declined in larger individuals on degraded reefs, showing species-specific coping.
- Dietary shifts suggest altered food webs and energy flow between healthy and degraded reefs.

## Abstract

The ability of consumers to adjust their diet in response to resource shifts is a key mechanism allowing the persistence of populations and 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 and the consequences of dietary shifts for consumer performance and ecosystem functioning remain poorly understood.Here, we tested how dietary versatility can mediate the effects of habitat degradation on two invertivorous reef fishes—Chaetodon capistratus, a browser, and Hypoplectrus puella, an active predator—and whether diet shifts relate to variation in body condition and growth.We integrated DNA‐based gut content analyses (metabarcoding), otolith analysis, body condition and field surveys to link diet profiles to growth and relative body condition across reefs differing in coral cover.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 healthier reefs, whereas it was annelid‐dominated on degraded reefs. We found significantly more variable body condition on degraded reefs in the browser, while the body condition of the active predator decreased in larger individuals on degraded reefs.Our results suggest that while dietary versatility serves as a mechanism to cope with degraded environments, the degree to which dietary shifts can buffer against the effects of habitat degradation varies between species. Overall, the variation in trophic niche across sites suggests that food webs and energy flow differ at relatively small scales between healthy and degraded reefs.

The ability of consumers to adjust their diet in response to resource shifts is a key mechanism allowing the persistence of populations and 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 and the consequences of dietary shifts for consumer performance and ecosystem functioning remain poorly understood.

Here, we tested how dietary versatility can mediate the effects of habitat degradation on two invertivorous reef fishes—Chaetodon capistratus, a browser, and Hypoplectrus puella, an active predator—and whether diet shifts relate to variation in body condition and growth.

We integrated DNA‐based gut content analyses (metabarcoding), otolith analysis, body condition and field surveys to link diet profiles to growth and relative body condition across reefs differing in coral cover.

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 healthier reefs, whereas it was annelid‐dominated on degraded reefs. We found significantly more variable body condition on degraded reefs in the browser, while the body condition of the active predator decreased in larger individuals on degraded reefs.

Our results suggest that while dietary versatility serves as a mechanism to cope with degraded environments, the degree to which dietary shifts can buffer against the effects of habitat degradation varies between species. Overall, the variation in trophic niche across sites suggests that food webs and energy flow differ at relatively small scales between healthy and degraded reefs.

Metabarcoding of gut contents shows that two common benthic‐feeding reef fishes with different feeding stratgies—a butterflyfish (Chaetodon capistratus) and a hamlet (Hypoplectrus puella)—shift diets on degraded reefs. These shifts mirror contrasting patterns in body condition: butterflyfish showed strong individual variation, whereas condition was only reduced in larger hamlets on degraded reefs, suggesting species‐specific coping mechanisms in response to coral loss.