Due to potential environmental problems in Sepetiba Bay, it is necessary to identify sites for environmental monitoring. Kutuca Beach was chosen for this purpose since community structure data from collections in 1999 detected high diversity. Over a period of 21 months, 63 taxa were collected (Chlorophyta, 22%; Ochrophyta, 16%; Rhodophyta, 62%). The destructive sampling used six random plots (25x25 cm) in each of two 20-meter long lines horizontal to the rocky shore. When the 1999 results were compared with these, it was observed that biomass went from 490.9±201.2 g.m-2 to 199.57±29.33 g.m-2, richness from 13.0±4.5 to 5.06±1.72, diversity H'=2.2±0.41 to H'=1.3±0.39 and equitability J'= 0.65± 0.06 to J'=0.55±0.17. Four taxa (Sargassum spp., Caulerpa sertularioides (S.G. Gmel.) M. Howe, Hypnea musciformis (Wulfen in Jacquin) J.V. Lamour. and Gracilaria cervicornis (Turner) J. Agardh) contributed 15% to 33% of the biomass, while in 1999, eight taxa (Caulerpa sertularioides,Dictyopteris delicatula J.V. Lamour., Gracilaria cervicornis, Sargassum spp., Codium taylorii P.C. Silva, Padina gymnospora (Kützing) Sonder, Galaxaura marginata (Ellis & Solander) J.V. Lamouroux and Hypnea spinella (C. Agardh) Kütz.) contributed 5% to 20% of the biomass. These results showed the existence of disturbance that probably is a consequence of dredging to increase the navigation channel to Sepetiba Port, as well as the entrance of cold fronts. In spite of fact that the invasive potential of the exotic species Kappaphycus alvarezii (Doty) Doty ex Silva was assessed as negative during this period, permanent monitoring of this species is recommended.
environmental monitoring; Marambaia island; phytobenthic assemblage; Sepetiba bay
