Diatomáceas em sedimentos superficiais da planície costeira da ilha do Marajó/Pará

Abstract

The coastal plain of Marajó Island is physiographically part of the Insular Estuarine sector of the Paraense coast. Field sampling was carried out at three points on the surface of different substrates (muddy and sandy), in the intertidal zones of Cajuúna, Pesqueiro, Araruna and Garrote, totaling 12 samples, analyzed according to conventional methods used for the analysis of diatoms in sediment. At Cajuúna, 37 taxa were identified, with Nitzschia sp3 (37%), Navícula sp1 (27.33%) and Cyclotella meneghiniana Kütz. (15.33%) being the most abundant, totaling 70% of relative abundance. At Pesqueiro beach, with 48 species, C. meneghiniana (13.67%), Tryblioptychus cocconeiformis (Cleve) Hendey (13%) and Thalassiosira sp1 (12%) were the species that reached the highest values of relative abundance. In Barra Velha, 37 species were identified. Nitzschia sp5 (37%), C. meneghiniana (17.67%), Caloneis sp2 (14.33%) and A. granulata (11%) reached relative abundance values above 70%. At Garrote, surface samples totaled 48 species, with Navícula sp1 (21%), Polymyxus coronalis L.W; Bailey (18.33%) and Cymatosira belgica Grunow (18.67%) as the most numerically expressive species. The analysis of the diatom assemblages showed differences in species abundance in the various environments of the coastal plain (mangrove, muddy/sandy tidal plain, salt field and tidal channel), linked probably, to the type of substrate, level of the tidal water column and presence/absence of vegetation. There is an increase in species richness from Cajuúna to Garrote, which may be related to the proximity of the mouth of the Paracauari River, which promotes greater contribution of freshwater species to the estuarine environment.