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Resource Availability Drives Large Differences in the Fine-Scale Spatial Pattern of Parrotfish Herbivory on a Coral Reef


Herbivory by fishes and sea urchins is a powerful mechanism on coral reefs that mitigates coral-algal competition by physically removing algae and creating bare space. The fine-scale spatial patterning of herbivory has the potential to foster coral recruitment by creating a spatially continuous refuge for coral settlement and survival. The temporal nature of grazing also has the potential to influence competitive outcomes between coral and algae by preventing algal dominance and consistently exposing bare substrate at a particular location. Here we explore the intraspecific variability in the fine-scale feeding behavior of a large, mobile coral reef herbivore on a small, pristine Central Pacific atoll. We document how two different resource regimes appear to drive differences in the social structure and the spatial and temporal feeding behavior of the Steephead Parrotfish, Chlorurus microrhinos. We report that feeding behavior is spatially focused when resources are abundant and regrow quickly, resulting in dense patches of bite scars (>100 bites m-2). There also appears to be a temporal periodicity to feeding behavior when resource are abundant and predictable, although our study duration did not allow for the precise timing between feeding bouts to be detected. We found that movement increases and feeding behavior is distributed sparsely across food patches when resources were scarce and recovered more slowly. The differences we report here occur at sites that are only a few kilometers away from one another, but result in dramatically different impacts to the benthos that could alter the survival of corals at their earliest life stages.

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