PRODUCTION AND REWORKING OF SEDIMENT BY PARROTFISHES (FAMILY SCARIDAE) ON THE GREAT-BARRIER-REEF, AUSTRALIA

Sediment produced by parrotfishes (family Scaridae) may comprise new b ioeroded material and/or reworked sediment. The relative contribution of the two components was examined in two bioeroding Chlorurus species , C. gibbus and C. sordidus, from Lizard Island in the Northern Great Barrier Reef, The relative importance of reworked sediment was determi ned based on direct estimates of sediment ingestion. In C. gibbus, 2.4 % of the sediment produced is reworked. In C. sordidus, reworking cont ributes 27.2 %. Comparisons of sediment size-distributions in epilithi c algal communities, gut contents and defaecation sites suggest that b oth C. gibbus and C. sordidus markedly decrease the particle size of s ediment as a result of ingestion and trituration in the pharyngeal app aratus.