Impact of Tapes philippinarum harvesting on nutrient dynamic in the Varano lagoon.

Lagoons are subjected to intensive fishing and aquaculture exploitation producing benefits to the human population but also sometimes ecological disturbance. Among these activities, harvesting of clams has important socio-economic and environmental implications for lagoon ecosystem. Harvesting of the clams could add to the general disturbance regime in the lagoon through damage to the benthic community but the effects upon sediment stability and biogeochemical cycles remain unclear. Sediments represent a ''recorder'' of water column processes and are the main storage and supply of nutrients which follows a release to the overlying water. Among important factors influencing nutrient release from sediments there are chemical physical parameters, sediment grain size, physical circulation and benthic disturbance. Human-induced resuspension effects often result from dredging operations that remove or redistribute sediments producing disturbance. During the last years, in the Varano lagoon there was an invasion by non indigenous clam species, Tapes philippinarum. The effect of harvesting of the clams was investigated after a short period of heavily not regulated fishing. Physical-chemical parameters, nutrients, chlorophyll a and total suspended matter values have been compared to previous samplings to assess hydrologic disturbance.