Distribution of sponges (Porifera) in the Biological Reserve of Atol das Rocas, NE Brazil

Abstract

Due to the richness and uniqueness of its fauna, Atol das Rocas harbours the first Marine Biological Reserve in Brazil, but only six species of sponges were previously recorded from the atoll. In the present study the structure of the sponge community in the Biological Reserve of Atol das Rocas is described through quali- and quantitative sampling in 18 collection sites. Thirty-six sponge species from 24 families were found, which summed with previous records makes a total of 39 species now known from the atoll. At least six species are new, and four (Plakortis sp.3, Clathrina sp., Holoxea violacea and Aplysina sp.) are provisionally endemic of Atol das Rocas. Total species diversity and evenness were moderately high (H=2.38, J=0.71), as well as total sponge abundance (14.2 ind.m-2). Spirastrella hartmani (5.4 ind.m-2) and Chondrilla aff. nucula (1.1 ind.m-2) were the most abundant sponge species in the atoll. Highest sponge diversity (H’= 2.13) and density (70.4 ind.m-2) were found at Fenda site, a cryptic environment with low water movement and 7m depth. The lowest diversity (H’= 0.22) and density (1.7 ind.m-2) were found at the shallow (10-30cm depth), exposed tide pools. Atol das Rocas shares several sponge species with Fernando de Noronha (13/39) and with the littoral of Pernambuco (12/39). The degree of endemism of the sponge community observed in the atoll was low (10%) if compared to New Caledonia reef for example (71%), but this number can increase with more collections and refinement of taxonomic studies.