Zooplankton composition along the confinement gradient of the Taranto Sea System (Ionian Sea, south-eastern Italy)

A 2-year study was conducted on 4 interconnected, progressively more confined coastal basins with the aim of describing zooplankton composition and its dynamics. A total of 346 taxa (175 species) were recorded. 24 species were new records for the Italian fauna. Taxa richness was partly attributed to the intense sampling effort. Using an additional net with narrower mesh sizes enabled to enrich the taxa list, and a correct estimation of the abundances, especially for the smaller species. Regarding spatial partitioning, 87.5% of categories were linked to only 1 or 2 adjacent sampling stations. Regarding time partitioning, 80.6% of categories showed an intermittent presence (seasonality). Distance from the open sea (confinement) was found to be directly correlated with the numerical abundance of specimens and its variability. In contrast, it was inversely correlated with species richness. Cumulative data after 2 years, confirmed the inverse correlation of species number with confinement. However, the final species richness led to less important differences between the four basins. A comparison with data from 1990 to 91 highlighted substantial differences in zooplankton composition. However, in one case it has been demonstrated that the difference was due to the difficulty in correctly estimating species number in confined habitats.