Bioerosion caused by foraging of the tropical chiton Acanthopleura gemmata at One Tree Reef, southern Great Barrier Reef

The bioerosive potential of the intertidal chiton Acanthopleura gemmata on One Tree Reef was determined by quantification of CaCO3 in daily faecal pellet production of individuals transplanted into mesocosms after nocturnal-feeding forays. Mean bioerosive potential was estimated at 0.16 kg CaCO3 chiton(-1) yr(-1). Bioerosion rates were estimated for populations on two distinct chiton habitats, reef margin (0.013 kg CaCO3 m(-2) yr(-1)) and beachrock platform (0.25 kg CaCO3 m(-2) yr(-1)). Chiton density on the platform was orders of magnitude greater than on the reef margin. The surface-lowering rate (0.16 mm m(-2) yr) due to bioerosion by the beachrock population is a substantial contribution to the total surface-lowering rate of 2 mm m(-2) yr(-1) previously reported for One Tree Reef across all erosive agents. At high densities, the contribution of A. gemmata to coral reef bioerosion budgets may be comparable to other important bioeroders such as echinoids and fish.