Meiobenthic and macrobenthic community structure in carbonate sediments ofRocas Atoll (north-east, Brazil)

Rocas is the only atoll of the South Atlantic and it is built almost exclus ively by coralline red algae, vermetid gastropods and encrusting foraminife rans. Patterns in the community structure of meiofauna and macrofauna, part icularly nematodes and polychaetes, at Rocas Atoll, north-east Brazil, are determined and compared for different habitats: sublittoral, tidal flat, re ef pools and lagoon. Nematodes and copepods were the most abundant meiofaun al taxa. In all studied habitats at Rocas Atoll, oligochaetes, nematodes an d polychaetes numerically dominate the macrofauna. Univariate and multivari ate analyses reveal clear differences in community structure between the ha bitats of the atoll, especially between the sublittoral and the inner habit ats. The number of species, total density, diversity (H') and trophic struc ture vary significantly between the habitats, but the differences are depen dent on which faunistic category (meiobenthic or macrobenthic) is analysed. Nematodes belonging to the Epsilonematidae and Draconematidae, together wi th a diverse community of meiobenthic polychaetes, characterize the sublitt oral habitat of Rocas Atoll. Both meiofauna and macrofauna are depressed in the tidal flat, and the local sediment instability particularly affects th e polychaete abundance. Reef pools and lagoons support a very dense aggrega tion of invertebrates, particularly the macrofauna, when compared with othe r carbonate reef sediments. However, differences in the structure of meiofa una and macrofauna communities between reef pools and lagoons are not signi ficant. Changes in meiobenthic and macrobenthic community structure are rel ated to the gradation in the physical environment of the atoll. (C) 1999 Ac ademic Press.