Mollusc diversity in Capo d’Armi (Central Mediterranean Sea) subtidal cliff: a first, tardy, report

First quantitative data on mollusc assemblages from the Capo d’Armi cliff, at the south entrance of the Strait of Messina, provided a baseline for monitoring changes in benthic biodiversity of a crucial Mediterranean area, whose depletion might already be advanced. A total of 133 benthic taxa have been recorded, and their distribution evaluated according to depth and seasonality. Bathymetric distribution showed scanty differences between the 4-6 meters and 12-16 meters depth levels, sharing all the 22 most abundant species. Season markedly affected species composition, since 42 taxa were exclusively recorded in spring and 35 in autumn, contrary to 56 shared taxa. The occurrence of some uncommon taxa has also been discussed. The benthic mollusc assemblages, although sampled in Ionian Sea, showed a clear western species composition, in accordance with literature placing east of the Strait the boundary line between western and eastern Mediterranean eco-regions. Opposite, occasional records of six mesopelagic species, which included the first record for this area of Atlanta helicinoidea, were linked to the local upwelling of Levantine Intermediate Waters.