Phytoplankton and environmental factors in the Paraíba do Norte River Estuary, northeastern Brazil: composition, distribution and quantitative remarks

Abstract

This paper reports the results obtained from studies on the estuarine phytoplankton of the Paraiba do Norte River in northeastern Brazil. Surface and near-bottom samples were taken at four stations numbered seawards, during high and low tides from September 1978 to September 1979. A total of 139 phytoplankters were encountered. Diatoms and dinoflagellates showed highest diversity in most saline areas. Typical freshwater organisms were restricted to stations I and II where salinity was more reduced. Maximum cell densities were: 11,256,000 cells/1, 4,380,000 cells/1, 1,276,000 cells/1 and 1,035,000 cells/1, for stations I, II, III and IV, respectively. Sewage enrichments were probably responsible for the greatest values of the first two stations. However, in these stations the turbidity reduces light penetration, limiting phytoplankton growth particularly during the rainy season. The phytoflagellates (maximum of up to 4,874,000 cells/1) and the diatoms Thalassiosira spp (maximum of up to 9,262,000 cells/1) were dominant during the annual cycle. Other important taxa were Navicula spp, Cylindrotheca closterium, Paralia sulcata, Thalassionema nitzschioides and the dinoflagellate Protoperidinium spp. Seasonal variations of phytoplankton densities, dissolved oxygen, phosphate, water transparency, temperature, salinity and suspended material are also presented.