Analysis of Lagoonal Ecosystems in the Po River Delta Associated with Intensive Aquaculture

Abstract

Observations on structure and functioning of coastal lagoon ecosystems experiencing a high level of eutrophication impact were accomplished in three lagoons of Ca’Pisani integrated within an experimental aquaculture enterprise variously fertilized by waste effluents discharged from and intensive fish culture plant. During August and early September an extremely dense bloom of dinoflagellateAlexandrium tamarensewas recorded in these lagoons with the density of phytoplankton up to 190gm−3of wet biomass, and primary production 2 to 6mgCl−1day−1. The diel dissolved oxygen fluctuations in water column during the bloom reached 15–20mgO2l−1. The wet biomass of bacterioplankton in the lagoons attained 5–9gm−3. The microzooplankton was dominated by ciliates with biomass 1 to 19 gm−3. The daytime mesozooplankton was dominated by calanoid copepods with a biomass 0·05–0·25gm−3, while the biomass of the demersal zooplankton at night attained 2 to 14gm−3. In the lagoon of Ocaro, the phototrophic plankton was dominated by the symbiotic ciliateMesodinium.The labile sulphides content in the upper layer of the bottom attained over 1gSdm−3of wet silt. The rate of microbial sulphate reduction was 5–10mgSdm−3day−1. The data are generalized within the energy balance in these specific anthropogenically transformed pelagic communities.