The studied area is limited by São Francisco River mouth, to the South, and by Coroa das Lavadeiras, State of Rio Grande do Norte, to the North. This area presents only two seasons, summer and winter. During the summer, the freshwater inflow is smaller, the southeast winds are dominant, the temperature, the salinity and the transparence of water are high. The winter is characterized by greater freshwater inflow, east winds, smaller temperature and low salinity and transparence only in coastal and estuarine waters. Off São Francisco River mouth the water conditions are inverted and the salinity and transparence variations affect all continental shelf. In the soft bottoms are found the following communities: a) Supralittoral beach; 2) Mediolittoral beach; 3) Infralittoral beach; 4) Circalittoral mud (São Francisco mouth); 5) Circalittoral gravel mud (São Francisco mouth).
