The composition of algal vegetation in and outside damselfish territories on a Florida reef

Abstract

Algal species composition and relative abundance inside and outside territories of Eupomacentrus planifrons (Cuvier and Valenciennes) and E. partitus (Poey) were investigated in a reef formation at 6-m depth at Molasses Reef, John Pennekamp Coral Reef State Park, Key Largo, Florida Keys. In total, 43 species of eukaryotic fleshy and filamentous algae were found inside 9 investigated E. planifrons territories, 35 inside 10 E. partitus territories, and 22 in 6 samples from undefended areas. Cover of fleshy and filamentous algae, as well as mean number of species per unit of surface area, were significantly higher inside E. planifrons territories than inside territories of E. partitus ( P<0.01) or outside territories of both fish species ( P<0.05). Filamentous blue-green algae were conspicuous both inside and outside damselfish territories. Relative cover of crustose corallines did not differ significantly between the three categories. Territories of E. planifrons were characterised by red algae belonging to the family Gelidiaceae and small branched corallines. Herposiphonia secunda (C. Ag.) Ambr. was characteristic of E. partitus territories, while no particular algal species was characteristic of undefended reef areas. The absence of some algal species outside defended areas is an indication that these species escape grazing inside territories. It is suggested that the species composition inside territories of E. planifrons and E. partitus depends mainly on the recruitment of spores which settle inside these territories and on differences in competitive ability between the algal species. Although the damselfishes have a pronounced effect on the density of the vegetation, there is no indication that they influence the species composition by weeding activities or by selective grazing.