Need for restricting bivalve culture in the southern basin of the Lagoon of Venice

At present, one of the environmental emergencies in the Lagoon of Venice is the impact of short-necked clam (Tapes philippinarum) fishery, which is pr actically an unregulated fishery. Although one of the proposed solutions wo uld be the restriction of Tapes fishery to licensed areas, high seeding den sity can cause undesired effects on the environment. In this study several hydrobiological variables are compared between small areas of the Lagoon of Venice traditionally used for bivalve culture (clam, T. philippinarum and mussel, Mytilus galloprovincialis), and areas in the southern basin with se agrass meadows. Labile and suspended organic matter in the water was higher in areas with bivalve farming than in Zostera areas (undisturbed control). The same pattern was recorded for contents of total organic matter and aci d volatile sulphides. The biomass of microplankton in farming areas was qui te high (0.8-2.7 g m(-3)). Mesozooplankton was extremely abundant, particul arly at night, when its biomass was 1-2 orders of magnitude higher than dur ing the day. Its composition was different in the culture areas and in Zost era areas. The biomass of Tapes in culture beds and their filtering capacit y were also estimated.