The infaunal community in experimentally seeded low and high density Manila clam (Tapes philippinarum) beds in a Po River Delta lagoon (Italy)

The Sacca di Goro is a shallow, brackish, eutrophic coastal lagoon in the southernmost part of the Po River Delta (northern Adriatic Sea, Italy). It is heavily exploited for rearing the Manila clam (Tapes philippinarum), mean annual production since 1986 being 10 000 t. Commercial cultivation of bivalves can exert severe impact on a local environment, especially on the invertebrate community, reducing species richness and abundance. An in situ experiment was conducted from March 2003 to February 2004 to examine the effect of clam cultivation on the macrobenthic community. Replicated sites within an area licensed for clam farming were seeded with low (500 m−2) and high (1500 m−2) clam densities; the surrounding unseeded areas were used as a control. There were only weak effects of clam presence and density on macrobenthic community abundance and functional group composition. The main determinants regulating the macrobenthic community were seasonal variations in other biota, particularly proliferation of the invasive mussel, Musculista senhousia, in August, which in turn caused a significant increase in the biomass of surface deposit-feeders and the subsequent development of Ulva rigida beds in September.