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Abstract
During the years from 1979 to 1984, macroalgal samples were taken every month in 15 stations, representative of the Venice littoral, in order to determine the species and the vertical distribution of phytobenthic associations. A great difference has been found with the results of previous papers (Schiffner & Vatova, 1938; Pignatti, 1962), due to the eutrophication increase. Many oligotrophic species, such as those belonging to the «Cystoseira association» have disappeared, whereas some genera, once very abundant, are presently strongly reduced, for instance Laurencia, Polysiphonia and Dasya. On the contrary many Ulvaceae have colonized all the studied area thanks to their adaptation to pollution. The percentage of Chlorophyceae has increased considerably, ranging from 20 to 34%, whereas Rhodophyceae decreased from 65 to 51%. Phaeophyceae percentage remained pratically unchanged ranging from 13 to 15%. Zostera marina, Zostera noltii and Cymodocea nodosa, once spread in all the lagoon, now only grow far from the urban wastes of Venice and the industrial effluents of Porto Marghera.
The limits of the deepest vegetational zones and the vertical distribution of their characteristic populations has also changed and many macroalgal species presently characterize higher level waters.
