Analysis of lagoonal ecosystems in the Po River delta associated with intensive aquaculture

Observations on structure and functioning of coastal lagoon ecosystems expe riencing a high level of eutrophication impact were accomplished in three l agoons of Ca'Pisani integrated within an experimental aquaculture enterpris e variously fertilized by waste effluents discharged from and intensive fis h culture plant. During August and early September an extremely dense bloom of dinoflagellate Alexandrium tamarense was recorded in these lagoons with the density of phytoplankton up to 190 g m(-3) of wet biomass, and primary production 2 to 6 mg Cl-1 day(-1). The diel dissolved oxygen fluctuations in water column during the bloom reached 15-20 mg O-2 l(-1). The wet biomas s of bacterioplankton in the lagoons attained 5-9 g m(-3). The microzooplan kton was dominated by ciliates with biomass 1 to 19 g m(-3). The daytime me sozooplankton was dominated by calanoid copepods with a biomass 0.05-0.25 g m(-3), while the biomass of the demersal zooplankton at night attained 2 t o 14 gm(-3). In the lagoon of Ocaro, the phototrophic plankton was dominate d by the symbiotic ciliate Mesodinium. The labile sulphides content in the upper layer of the bottom attained over 190 g dm(-3) of wet silt. The rate of microbial sulphate reduction was 5-10 mg S dm(-3) day(-1). The data are generalized within the energy balance in these specific anthropogenically t ransformed pelagic communities. (C) 1999 Academic Press.