Intense fish herbivory is critical to maintaining healthy coral reefs by limiting algal proliferation. Healthy herbivore populations are maintained partly by the high structural complexity of coral reefs by providing refuge from predators. However, coral reef ecosystems are increasingly losing structural complexity due to anthropogenic stressors, potentially disrupting the behavior of herbivorous fishes. We examined the relationship between the structural complexity and the anti-predator behavior of a common herbivorous fish, Ancanthurus nigrofuscus, on a fringing reef of Mo’orea, French Polynesia. We compared anti-predator behavior in 3 paired plots that differed significantly in rugosity (LME, p=0.0068). Across 181 replicate behavioral trials, individual fish hid from an approaching snorkeler more frequently in high rugosity plots but fled more often in low rugosity plots (chi-squared, p<0.0001). However, counter to predictions, fish size or plot rugosity had no impact on flight initiation distance (LME, p=0.539). This change in fish behavior could have far-reaching implications, as declines in structure that result in fish fleeing more could reduce total herbivory, potentially triggering cascading effects that accelerate the global decline in coral reef ecosystems. Thus, understanding these dynamics is essential for mitigating the ongoing deterioration of reef ecosystems

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