FORAGING BY THE STOPLIGHT-PARROTFISH SPARISOMA-VIRIDE .2. INTAKE AND ASSIMILATION OF FOOD, PROTEIN AND ENERGY

Daily food intake by the herbivorous parrotfish Sparisoma viride, as w ell as assimilation efficiencies of algal food, protein and energy, we re quantified through a combination of laboratory feeding trials and f ield observations. The intake of algal ash-free dry wt (AFDW) per bite increases linearly with fish wet wt (FWW, g) and algal biomass (mg AF DW CM-2), and is further determined by the skeletal density of the lim estone substrate. Low-density substrates yield higher amounts of AFDW per bite than do high-density substrates. The percentage of the total food intake that is derived from endolithic and crustose coralline alg ae increases with the size of the fish, and can be > 70 % depending on the biomass of epilithic algae. The daily pattern of foraging activit y is positively correlated with diurnal changes in food quality, while seasonal daylength variations result in 13 % variation in total daily bites taken. Daily number of bites of S. viride in the field decrease s with fish size, and is further dependent on life phase and foraging depth. In experiments, fish attained an assimilation efficiency of ca 20 % from a natural diet of low algal biomass and high-density dead co ral substrates that predominates in the shallow reef. Assimilation eff iciency was ca 70 % from a diet of high algal biomass and low-density substrates that predominates on the deeper reef parts. In spite of low er daily foraging effort, territorial fish, living in deeper parts of the reef, ingest and assimilate higher amounts of AFDW, protein and en ergy per day than non-territorial fish foraging on the shallow reef. T he difference is caused by increased availability of high-yield food a nd substrate types inside territories compared to the situation on the shallow reef. Daily assimilated energy (kJ d-1) is 0.85 x FWW 0.773 f or fish foraging in the shallow reef zone, and 1.22 x FWW0.854 for S. viride foraging inside territories on the deeper reef.