CARBONATE TRANSPORT AND WITHIN REEF PATTERNS OF BIOEROSION AND SEDIMENT RELEASE BY PARROTFISHES (FAMILY SCARIDAE) ON THE GREAT-BARRIER-REEF

The patterns of erosion and defaecation by 2 species of parrotfish Chlorurus gibbus and C. sordidus (family Scaridae) were examined at 2 sites on Lizard Island, Great Barrier Reef, Australia. Feeding behaviour and associated external bioerosion were examined at 3 spatial scales: reef zone, microhabitat and bite site. Feeding patterns in both species showed strong selectivity for specific reef zones, microhabitats and substratum types. Both species fed predominantly in the shallows, with strong preferences for coral stumps. C. gibbus strongly selected the reef crest and turf algae at both sites. C. sordidus showed differential selectivity at the 2 sites. It is suggested that these site and species differences are a result of interactions with territorial herbivores. In C. sordidus the patterns of feeding and defaecation across the reef were extremely similar. There was no net movement of material. In contrast, C. gibbus showed a strong preference for feeding in shallow reef zones, with defaecation marked by movement away from feeding areas to specific defaecation sites, usually in deeper areas of the reef. This resulted in an active net movement of carbonate off the reef.