Abstract

In order to estimate the amounts of organic carbon and nitrogen flowing through a herbivorous fish, ingestion, absorption, defecation and excretion were studied in a widely distributed fish in coral reefs, the black damselfish Stegastes nigricans. Two study sites were chosen on a coral reef at La Réunion, in summer. One site is oligotrophic (site O), while the other is nutrient-enriched (site D for disturbed), subject to submarine groundwater discharges. Ingestion and defecation activities were monitored by recording bites rates and faeces production, and excretion quantified by in vitro experiments. Feeding activity (number of bites and faeces) and individual trophic fluxes were larger at site D than at site O. More algal food and thus more organic carbon and nitrogen were consumed, absorbed and redistributed into the reef system by an individual fish at site D than at site O, suggesting a positive feed-back of herbivores on nutrient-enrichment.