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) and is heavily exploited for rearing of the Manila clam Tapes philippinarum, where mean annual production is 10000 tonnes, since 1986. Commercial cultivation of bivalves can exert severe impact on the 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 variation of other biotic components, particularly the proliferation of the invasive mussel, Musculista senhousia, in August, causing a significant increase in surface deposit feeders, and the subsequent development of Ulva rigida beds in September.