Diatomáceas em Sedimentos da Praia de Itupanema, Barcarena, Pará: Análise da Composição, Abundância e Diversidade de Espécies

Abstract

Diatoms are used in paleolimnological and paleoenvironmental studies because of their preservation in sediments, high reproductive rate and rapid response to changes in nutrient composition and other water quality variables. We analyzed the ITI (42 cm) and IT2 (20 in) clay-sand samples collected from Itupanerna beach, municipality of Barcarena, Pará. In the laboratory of Paleopalinology and Paleoecology/CCTE/MPEG, 2 in3 subsamples of ITl (8) and IT2 (4) were taken at 3 cm intervals and treated according to conventional techniques (RIBEIRO et al., 2005). Three slides were made for diatom identification and counting of 300 valves/level, under a ZEISS light microscope. Data included the estimation of species richness, relative abundance, frequency of occurrence, diversity (Shannon) and equability. Along IT1, there were strong variations in species richness, diversity and equitability, where Polymyxus coronalis stood out at the base, with abundance around 94 %, gradually decreasing towards the surface. In IT2, P. coronalis had lower abundance values (16.3 %) at the base, presenting the same trend observed in ITl. However, richness, diversity and equitability in IT2 did not undergo great variations. Aulacoseira granulata was the most representative species in terms of abundance (46.7 %) and frequency (100 %). There was a continuous increase of its abundance (0-47.8 %), towards the surface in IT2, evidencing increased limnetic conditions and higher nutrient contents. The distribution of species in the cores was associated with changes in nutrient levels and substrate grain size, indicated by the ecological specificity of the most abundant and frequent taxa. The biological data also indicate changes in salinity.