Macrobenthic Community Changes Related to Eutrophication inPalude della Rosa(Venetian Lagoon, Italy)

Changes in macrozoobenthic communities were studied in a shallow eutrophic basin known as thePalude della Rosain the Venetian lagoon, Italy. The sampling was conducted on a monthly basis from December 1991 to July 1993 at four representative stations. The observed fluctuations of the benthic community structure closely followed the seasonal cycle of the green macroalgaUlva rigidaC. Ag., and its overgrowth. Sediment enrichment in organic matter, due to this algal overgrowth, modified the environmental conditions, leading to anoxic crisis over the summer. Significant differences in community composition and diversity were found between those stations that were heavily influenced byUlvapresence and those less influenced. All species were strongly affected by the crisis; so much so that benthic macrofauna almost disappeared. This period was then followed by a recolonization phase of the devoid bottom. Such a recolonization took place over the following winter, following a pattern similar to that found in other studies of organic enrichment elsewhere. The community structural changes were analysed by means of univariate and multivariate techniques.