UC San Diego

Robust parrotfish assemblages have been shown to control algal proliferation and promote the settlement of corals and crustose coralline algae (CCA). At relatively high densities, parrotfish have been suggested to negatively affect net reef accretion through bioerosion and targeted corallivory. Most evidence describing the impacts of parrotfish grazing are based upon correlations benthic change and behavior or abundance, with less known about process-based change of individual parrotfish bite scars through time. We estimated parrotfish grazing selectivity and determined the change in composition of parrotfish bite scars relative to change in the overall landscape using data collected from the fore reef habitat at Palmyra Atoll. We identified over 2100 parrotfish bite scars estimated the substrate they were taken on, and described the change in benthic composition within the scar area identified over the 12 month duration of the study. Bite scars were most abundant on turf algae, but were found on all dominant benthic functional groups. Of bites taken on coral, 96% of scars returned to complete coverage of live coral by the end of the study, while only 67% of points on coral remained alive during this study across the overall reef. Further, coral recruitment to bite scars was virtually nonexistent (n=1). Change within bite scars was dependent on the composition of the surrounding substrate, but 33% and 38% of bites on turf and mixed turf/CCA, respectively, progressed to CCA. Successional trajectories on bite scars, compared with change on the overall reef landscape, suggest parrotfish grazing maintains a calcifier-rich benthos.