Herbivory by the Dusky Damselfish Stegastes fuscus (Cuvier, 1830) in a tropical rocky shore: effects on the benthic community

Experiments were carried out on rocky shores at Arraial do Cabo (Southeast Brazil) to evaluate how the dusky damselfish, Stegastes fuscus (Cuvier, 1830) affects the benthic community structure. Cage exclusion showed that S. fuscus strongly influences the algal community in its territories, keeping it in an early succession stage and,preventing dominance by Jania spp. Diversity and biomass of the epilithic algal community (EAC) were higher inside territories than outside. These dense mats hold a diverse and abundant cryptofauna (congruent to 72 ind/100 cm(2)) that was significantly higher inside territories. Algae comprise 70% of the S. fuscus diet, with the remaining 30% composed of animal material. The fish feeds selectively mainly on red filamentous algae, such as Polysiphonia spp., Ceramium spp. and Centroceras clavulatum, albeit it also ingests a great amount of calcareous algae (25% of total algae); Total assimilation and nitrogen assimilation were low in S. fuscus. Gut contents turnover varied from 3.7 in summer to 4.1 in winter. The net primary productivity (NPP) values of EAC within territories were intermediate ranging from 0.86 to 2.34 gC day(-1) territory(-1) in winter and in summer, respectively. Grazing rates did not vary greatly between seasons. In summer damselfish do not appear to affect production on territories, but in winter consumption could remove 100% of primary production, indicating a high turnover rate by EAC. S. fuscus plays an important trophodynamic role in this system, since its abundance is high and overall energy flux is enhanced inside its territories. (C) 1998 Elsevier Science B.V. All rights reserved.