- Samples of the staghorn coral Acropora were taken from within territories defende by damselfish (Pisces: Pomacentridae) and from undefended areas. The fish utilized in this experiment were Hemiglyphidodon plagiometopon Bleeker and Pomacentrus bankanensis Bleeker. The extent of bioerosion was determined by randomly selecting pieces of coral substrate from treatment and control areas, cutting transverse sections, and determining total eroded area with the aid of enlarged photographs. Boreholes within the photos were traced with a digitizing sensor and area was integrated with the aid of a computer.Corals inside territoties were significantly more bioeroded (p<0.001) than corals outside areas. Most of the destruction was caused by boring sponges (Cliona sp.) and sipunculids (Cleosiphon). It is suggested that bioerosion is accelerated within territories as a result of reduction in grazing by fish.