COMPARATIVE-ANALYSIS OF FORAGING AND HABITAT USE BY THE SYMPATRIC CARIBBEAN PARROTFISH SCARUS-VETULA AND SPARISOMA-VIRIDE (SCARIDAE)

On the fringing reef of Bonaire, Netherlands Antilles, a comparative s tudy was made of habitat use, diet selection, foraging behaviour and f ood acquisition of the parrotfish species Scarus vetula and Sparisoma viride. The species are sympatric and live in the same reef habitats ( depth zones). Both species show similar foraging selectivity, but expl oit algal resources differently. Preferred food items are turf algae o n substrates infested with endolithic algae, whereas crustose corallin es are avoided. Foraging preferences are related to yield, i.e. the am ount of AFDW (ash-free dry weight), protein and energy that can be har vested per bite. Foraging behaviour differs between the species. S. ve tula takes more bites in long forays, has higher bite rates (no, of bi tes s(-1)), and makes fewer and smaller scars on grazing substrates th an S. viride. Furthermore, S. vetula prefers flat substrate surfaces w hile adult S. viride graze by preference on concave surfaces. Species- specific differences in preference and utilization of grazing substrat es are related to feeding mode. S. vetula employs a scraping feeding m ode by which mainly epilithic algae are ingested. In contrast, S. viri de is an excavating grazer that ingests large amounts of endolithic an d crustose algae. Intake and assimilation of algal AFDW, protein and e nergy were quantified through a combination of laboratory feeding tria ls and field observations. S. vetula has lower food intake (mg AFDW bi te(-1)) than S. viride (0.8 x 10(-3) x fish wet wt, FWW, and 2.3 x 10( -3) x FWW respectively), resulting from smaller (shallower) bites. Ass imilation efficiencies of total AFDW, protein and energy by S. vetula were higher than in S. viride grazing on the same dead coral substrate s, In spite of different feeding modes and different fractions of the primary production harvested, daily amounts of assimilated nutrients a nd energy are similar for both species, resulting from higher feeding rates (no. of bites h(-1)) and higher assimilation efficiency in S. ve tula.