Ingestion and transformation of algal turf by Echinometra mathaei on Tiahura fringing reef (French Polynesia).

The sea urchin Echinometra mathaei is the most abundant herbivore on many tropical reefs. We studied the ingestion and digestion diel rhythms, transformation of algal turf and bioerosion attributable to this species on the Tiahura fringing reef in French Polynesia. Ingestion rates showed a circadian rhythm with most feeding taking place during the night. Absorption of food occurred throughout the day with urchins digesting food outside of the feeding period. A total of 73% of the faecal pellets consisted of CaCO(3) eroded from the reef, 20% consisted of organic matter and 7% the refractory organic matter. Of the organic matter, lipids, carbohydrates and chlorophyll were digested and absorbed and proteins were expelled in the faecal pellets. An average individual bioerosion of 0.32 g day(-1) was estimated for E. mathaei from approximately a 35-mm test diameter on the Tiahura fringing reef. We further estimated that E. mathaei release 70.5 g m(2) y(-1) of carbohydrates, 43.8 g m(2) y(-1) of lipid, 23.3 g m(2) y(-1) of protein and 2.0 g m(2) y(-1) of total chlorophyll pigments.