SPATIAL DISTRIBUTION OF PLANKTON COMMUNITIES ALONG A SALINITY GRADIENT IN THE VENICE LAGOON ITALY

With the aim to describe the distribution of the plankton communities, a series of samplings were carried out on February, 1983, on 14 stations located along a salinity gradient in the northern basin of the Venice lagoon. Hydrological (temperature, salinity, pH, dissolved oxygen concentration) and biological parameters (chlorophyll a content, phyto- and zooplankton abundances) were observed during ebb and flood, spring and neap tide. Salinity gradients modifies the spatial distribution of the communities, especially inside the phytoplankton assemblage. Using the Principal Component Analysis and the Cluster Analysis, we discriminate three groups of phytoplankton associations, each of them characterized by the presence of guide species in close relationship with the water bodies. Zooplankton community was dominated by the presence of one species in the sampling period. Salinity acts even on plankton diversity. Diversity index decreases together with salinity, increasing only as phytoplankton assemblage is concerned proceeding to diluted waters.