Meiobenthic biodiversity in areas of the Gulf of Taranto (Italy) exposed to high environmental impact

Biological and chemical parameters (meiofauna density and diversity, redox profiles) were investigated in relation to the environmental conditions of sediments in the Gulf of Taranto. Sediment cores were collected from 42 stations from 5 to 20m depth, in 1995, 2000 and 2001. Meiofauna abundance and diversity were significantly lower in the Mar Piccolo, the area most heavily polluted by organic loads; in Mar Grande and Chiatona areas the same parameters showed slightly higher values. Eh profiles revealed anoxic conditions in coastal sediments impacted by industrial and sewage discharges. Meiofauna density ranged from 186 to 1370 individuals 10 cm 2. Generally, over 80% of total meiofauna was composed of nematodes; the contribution of other taxa is much less important. The widespread presence of the lessepsian Chlorophyte Caulerpa racemosa since 1996, seemed to enhance the abundance of meiofauna, and increased microhabitat complexity, but reduced diversity of some taxa, such as the meiobenthic crustaceans. Comparing 2001–2002 data with 1995 (before C. racemosa invasion), the recent decrease of some groups (ostracods, amphipods, isopods, tanaids and cumaceans) was markedly evident. In conclusion, our findings confirm the chronically degraded environmental conditions in the Gulf of Taranto, and draw attention to the further contribution of C. racemosa invasion.