The effect of a natural water-movement related disturbance on the structure of meiofauna and macrofauna communities in the intertidal sand flat of Rocas Atoll (NE, Brazil)

Rocas, the only atoll in the South Atlantic, is located 266 km off the nort heast Brazilian coast. Spatial patterns in community structure of meiofauna , particularly nematodes, and macrofauna were examined along a transect thr ough the sediment path from windward to leeward of the Rocas Atoll sand fat . Differences in benthic community structure between four zones of the sand flat were found to be significant and related to the major local processes of carbonate-grain transport and sedimentation. Both meiobenthic and macro benthic assemblages were significantly more diverse and abundant within the sediment inflow zone (the initial part of the detrital path of Rocas sand flat) than in the other zones, where a clear impoverishment of benthic inve rtebrates occurred. This first study of the benthos of an inter-tidal sand flat over a reef island in the Atlantic showed that the meiofauna is numeri cally dominated by the nematodes Metoncholainus sp. 1 (Oncholaimidae) and E psilonema sp. 1 (Epsilonematidade), whilst the macrofauna is largely domina ted by oligochaetes and large Oncholaimidae nematodes. Analysis of the spec ies composition, trophic structure and abundance of both the meiobenthos an d the macrobenthos revealed an impoverished community subjected to an inten se water-movement disturbance. (C) 1999 Elsevier Science B.V. All rights re served.