Seasonal and spatial structure of microphytoplankton in the tropical estuary of Formoso River, Pernambuco State, Brazil

(Seasonal and spatial structure of microphytoplankton in the tropical estuary of Formoso River, Pernambuco State, Brazil). This work aimed to evaluate spatial and temporal variations of the microphytoplankton and environmental variables in the Formoso River estuary, southern coast of Pernambuco state. The samples were collected at three stations, in the rainy season (May to July/2002) and dry season (October to December/2002). The plankton samples were obtained through horizontal superficial hauls, with a 64im-mesh net. Temperature and transparency were recorded in situ and, at the same time, water samples were collected using a Kitahara bottle to analyze salinity, pH, dissolved oxygen, nutrients and biomass. A total of 204 taxa were identified with the diatom group (75%) ranking first; dominant species were Chaetoceros costatus Pavillard, Chaetoceros curvisetus Cleve, Chaetoceros sp., Coscinodiscus centralis Ehrenberg, followed by the dinoflagellates (10.79%), cyanophycea (6.37%), chlorophycea (3.92%), euglenophycea (3.43%) and silicoflagellates (0.49%). Oxygen concentrations evidence a high capacity of environment renewal due to sea-water input; higher concentrations of nutrients and microalgae biomass occurred during the rainy season and at low tide. The parameters rainfall and sea-water input influenced hydrology and phytoplankton community distribution to the greatest degree, contributing to species richness.