FEAR AND FLATTENING: REEF HABITAT COMPLEXITY ALTERS REEF FISH FORAGING BEHAVIORS
Date
2024
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Abstract
A robust and diverse reef fish community is generally reflective of healthy, resilient reefs. Herbivorous fishes play a critical role in controlling algal populations on coral reefs, yet they are increasingly threatened by human pressures and other climate stressors. These fishes often concentrate their grazing near the protective refuge of coral reefs due to perceived predation risk. With increasing coral degradation due to bleaching and subsequent coral mortality, benthic complexity is lost, yet the impact of this loss on herbivore foraging behavior is unclear. This study employed a space-for-time substitution to assess how varying levels of reef structural complexity influence reef fish biodiversity and foraging behavior in Kāne‘ohe Bay, O‘ahu, Hawai‘i. Reef complexity was quantified using Structure-from-Motion (SfM) photogrammetry, while fish community structure (biodiversity, abundance) and foraging behaviors (foraging frequency, distance traveled from reef, and number of bites) were recorded through in-situ surveys. Results revealed that reef complexity significantly influenced species richness and foraging patterns. While fish species richness showed a positive association with reef height, reef fish abundance exhibited a more nuanced relationship which was influenced by site-specific variability. Herbivorous fish tended to concentrate foraging closer to reef margins as structural complexity decreased, whereas higher complexity reefs supported foraging further from the reef’s edge. This pattern was dominated by genera such as Acanthurus and Zebrasoma, which tended to forage farther from the reef margin, and Chlorurus, Ctenochaetus, and Scarus which foraged closer. Notably, this trend was consistent across complexity levels, as no significant differences in foraging behavior were observed for the herbivore species studied. These findings highlight the critical role of reef structural complexity in shaping fish community dynamics and behavior. The degradation of reef complexity may confine herbivore foraging to areas near remaining reef structures, potentially creating a feedback loop where reduced complexity promotes algal colonization, further diminishing reef health and resilience.
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Biology, Coral reefs, foraging risk, herbivorous reef fish, spatial patterns, structural complexity, structure from motion
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29 pages
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