Algal food processing by Stegastes nigricans, an herbivorous damselfish: differences between an undisturbed and a disturbed coral reef site (La Reunion, Indian Ocean)

There has, as yet, been little study of nutrient disturbance and its conseq uences on the functional biology of primary consumers in coral reefs. The p rocessing of epilithic algal communities by the damselfish Stegastes nigric ans was investigated at La Reunion, at two sites of a fringing reef, oligot rophic for one and eutrophic for the other. Differences between sites were analyzed in quantifying organic matter, organic carbon, nitrogen, and organ ic 'nutrients' (carbohydrate, lipid and protein) in the algal food, the dig estive contents and the faeces of S. nigricans. In the disturbed site, alga l turfs and digestive contents presented significantly higher organic matte r, organic carbon, nitrogen and organic nutrient values. Absorption efficie ncy of total matter was higher in fish from this site (26.8 %) than from th e undisturbed site (16.3 %), as well for organic matter, organic carbon, ni trogen and organic nutrients. A larger mean total length was also measured for fish sampled in the disturbed site (11.4 cm versus 10.9 cm). The reinje ction of organic nutrients by this herbivorous fish appeared to be enhanced in this site. It is suggested that eutrophication is the main disturbance factor accounting for the recorded differences. (C) 2000 Ifremer/CNRS/IRD/E ditions scientifiques et medicales Elsevier SAS.