Vertical distribution of benthic marine organisms on rocky coasts of the Fernando de Noronha Archipelago (Brazil)

Abstract

Qualitative samples of flora and fauna were collected in several points, from the supralittoral fringe down to 30 m, using mainly aqualungs. Species distribution and abundance were determined along four transects, up to 200 m long, in selected places. Samples were taken from 25 x 25 cm quadrats positioned at fixed intervals along the transects down to a variable depth, depending on algal percentage cover and their substrate. The intertidal zone was populated essentially by molluscs. The subtidal was covered predominantly by macroalgae. Montastrea cavernosa, Siderastrea stellata and Mussismillia hispida were the only animal species with a significant percentage cover within the quadrats. Dictyopteris justii, D. plagiograma, Dictyita cervicornis, D. linearis, D. mertensii, Sargassum platycarpum, Sargassum sp, and Stypopodium zonale were the plants with the highest biomass and/or percentage cover, along with Amphiroa fragilissima, Caulerpa verticillata, and crustose corallines. The scarcity of sea urchins, along with the dominance of algae known to produce chemical feeding deterrents or to have a calcareous nature, points towards a strong pressure by predators, with fishes probably playing a key role in the maintenance of the structure of this subtidal community.