IL MACROZOOBENTHOS.

Macrobenthic samples were collected in 4 sites inside the Acquatina lake (3 replicates for each site in two times: July 2006 and January 2007). A total of 5029 individuals belonging to 50 taxa were found, with molluscs taxonomically dominant (26 taxa), followed by polychaetes (19 taxa), which was instead numerically dominant due to the massive presence of the species Heteromastus filiformis. Data were analysed by multivariate techniques. The assemblage was quite homogeneous within the lake, with more quantitative than qualitative differences among sites. Statistical analysis showed two sites, representing the two extreme of the biotope condition, as the most variable ones and separated from the others, located in the middle of the investigated biotope. The separation of the two sites from this central more homogeneous area was due to a different distribution between molluscs and polychaetes species. The comparison of the polychaete distribution between data relative to a previous period of study and present ones revealed a more diversified assemblage, with the disappearance of some opportunistic forms, and with an homogenization within the basin, underlining the disappearance of the strong salinity gradient.