ON AN EXTREMELY DENSE BLOOM OF THE DINOFLAGELLATE ALEXANDRIUM-TAMARENSE IN LAGOONS OF THE PO RIVER DELTA - IMPACT ON THE ENVIRONMENT

An extremely dense bloom of the potentially toxic dinoflagellate Alexa ndrium tamarense was observed in the lagoons of Ca Pisani (Veneto, Ita ly) in summer 1993. The lagoons were experiencing a significant eutrop hication impact, receiving waste waters from intensive fish culture pl ants. During their bloom dinoflagellates in the lagoons reached densit ies of 2 to 4 x 10(6) cells . dm(-3) and a biomass of over 100 g . m(- 3). The bloom produced drastic ecological changes in the lagoons. It c aused nocturnal anoxia, mortality of macrophytes and the build-up of l abile organic matter in the water column. Grazing by the tintinnid Fav ella sp. contributed to the termination of the bloom of the flagellate s. The results show that coastal aqua culture probably stimulates dino flagellate blooms in shallow brackish lagoons.