Is rate of removal of algae by grazers reduced inside territories of tropical damselfishes?

Abstract

This paper describes an experiment designed to measure the standing crop and the per unit area rates of production of algal tissue and yield to large grazers of the epilithic algal community (EAC) inside and outside the territories of the herbivorous pomacentrid Stegastes fasciolatus (Ogilby) on an outercontinental shelf coral reef in the central Great Barrier Reef. Standing crop of the EAC was significantly higher inside(29.25 g C· m −2,95% C. L. = 2.59) than outside (18.45 g C· m −2,95% C. L. = 3.02) territories. Rates of production of algal tissue inside and outside territories were respectively 1.20 (95% C. L. = 0.23) and 0.69 (95 % C.L. = 0.22) g C · m −2· day −1 . Rates of yield to large grazers inside and outside territories were respectively 0.98 (95% C. L. = 0.33) and 0.48 (95% C. L. = 0.39) gC· m −2· day −1.Neither production of algal tissue nor yield were significantly higher inside than outside territories because of high within-site variances. Rate of production of algal tissue did not differ significantly from yield both inside and outside territories. Grazing intensity measured as bite rates may be lower inside than outside territories but grazing intensity measured as rate of removal of algal tissue may be as high, if not higher, inside than outside territories.