Comparison Between the Energy Flow Networks of Two Habitats in the Venice Lagoon

The energy flows of two habitats are quantified and compared by using a trophic network model. The habitats are representative of two typical subsystems of the Venice Lagoon: the seagrass meadows, which represent a mature stage in the ecological succession of lagoon environments, and the Tapes philippinarum fishing grounds, which are subjected to mechanical clam harvesting. The results obtained for the 'seagrass habitat' are consistent with other field studies, confirming the 'key-stone' role played by phanerogams in a lagoon environment. The results for the 'Tapes habitat' show that the energy flow from the sediment to the water column is extremely important. Indeed, the high T philippinarum biomass cannot be supported solely by the primary production of the local phytoplankton. Instead, this biomass could be supported by a supply provided by the sediment resuspension caused by intensive clam fishing. These findings suggest the presence of a positive feedback between fishing effort and T philippinarum standing crop.