Characterization and Biogeographic Affinity of Megazoobenthos in the Central Mediterranean Sea

The Strait of Sicily (SoS) is a key area in the Central Mediterranean Sea characterized by high biodiversity and demersal fisheries productivity. Further, it is traditionally considered the main biogeographic boundary between the Western and Eastern basins of the Mediterranean. Due to the poor knowledge on the benthos composition and distribution in this area, we created the first inventory of megazoobenthos recorded on the trawlable soft bottoms of the North-Western SoS. Samples were collected by bottom trawl surveys between 2003 and 2013 within a depth range of 10-800 m. Overall, 374 taxa with 358 species, belonging to Porifera, Cnidaria, Nemertea, Rotifera, Brachiopoda, Bryozoa, Sipuncula, Annelida, Mollusca, Arthropoda, Echinodermata and Chordata phyla, were found. In addition, the biogeographic affinity of megazoobenthos collected in the SoS to species vulnerable to trawl survey found in other zones of the Central Mediterranean was investigated. Excluding the North Adriatic and the Strait of Messina, moderate affinity values have been recorded within all the biogeographic zones. The benthos species of the North-Western SoS presented the highest affinity with those of the North Tyrrhenian and Ligurian Sea (about 90% of species in common). However, our results show high similarity with species composition of the South-Eastern SoS/South Ionian, North Ionian and Central Adriatic (about 80% of species in common). Our study confirms the role as biogeographic transition zone of the SoS for the Mediterranean biota. Furthermore, the lower affinity with native species of the South-Eastern SoS and the absence of Lessepsian species suggest that the cold waters (due to the permanent up-welling) off the southern coasts of Sicily may act as thermal barrier for regulating species exchange between the Eastern and Western basins. Some concerns about this role of the northern sector of the SoS were discussed in the light of current climate change.