Ecologia do fitoplÃncton de um ambiente tropical hipersalino (Rio Pisa Sal, Galinhos, Rio Grande do Norte, Brasil)




The environments at the Northeast coast of Rio Grande do Norte State are under strong anthropic stress (mainly oil exploration, salt production and marine shrimp culture expansion etc). The present study was conducted in the Pisa Sal River estuary, which belongs to Galinhos-Guamarà ecocomplex, and provides the main water supply and drainage to the Camarus shrimp culture farm. The present research was carried out to assess the influence of these activities on phytoplankton composition and biomass along with the abiotic parameters as environmental quality indicators. Sampling was made in three fixed stations during the dry (September, November/02, January, May, July/03) and rainy (March/03) seasons, at the diurnal low and high tides, in a spring tide. Climatological (temperature, humidity, rainfall, insolation, evaporation, wind velocity and direction) and hydrological (tides, depth, water salinity, pH and dissolved oxygen) data were collected to correlate with the biological (chlorophyll a and microphytoplankton species composition) data. The microphytoplankton was collected with the plankton net of 38 micrometers of mesh size. Besides, the light extinction coefficient, the dissolved oxygen saturation rate, the microphytoplankton abundance, the microphytoplankton frequency of occurrence, species diversity, evenness, date and the observed dissimilarity among stations were collected and pooled to test the significance in Principal Component Analysis (PCA). It was identified 210 phytoplankton taxa, the diatoms species are overwhelming followed by dinoflagellates, blue-greens algae, and a few species of euglenophyceae. The flora was composed by true marine planktonic species (neritic and oceanic) and tycoplanktonics, demonstrating the direct influence of the coastal marine water. However, some freshwater species were registered due the rivers influence in this ecocomplex. The most dominant and abundant species were Thalassiosira subtilis, Thalassionema nitzschioides, Asterionellopsis glacialis and Chaetoceros danicus. Species diversity and evenness were high showing a well balanced community and influenced by the climatological (density independent) parameters. The PCA showed a direct correlation among chlorofill a, dissolved oxygen, water and air temperatures, Asterionellopsis glacialis, Chaetoceros danicus, Pleuro-Gyrosigma sp., Rhizosolenia setigera, Thalassionema frauenfeldii and Thalassionema nitzschioides. The analyzed results show that the Pisa Sal River estuary is hyperhaline, with a strong marine influence. Although the dissolved oxygen is high the environment is eutrophic, towards a tendency of hypereuthrophic condition during the rainy season, presenting already a deteriorating condition


hyperhaline biomass eutrophic hipersalino oceanografia biomassa taxonomia taxonomy fitoplÃncton eutrÃfico pisa sal river estuary estuÃrio do rio pisa sal phytoplankton

Documentos Relacionados