Crustacea Decapoda from Ustica (Southern Tyrrhenian Sea): species distribution and sampling approach.

The decapod crustacean fauna of Ustica Island (Sicily, southern Tyrrhenian Sea) has been investigated in summer 2002 with the aid of many different sampling methods: suction device, pushnet, skid trawl, trammel net, traps, underwater observation, interviews. All the substrata occurring around the island from 0 to about -30 m were surveyed: midlittoral rock, infralittoral rock, pebbles, seagrass (Posidonia oceanica) bed, sand, detritic bottom, submerged cave. Fiftyseven species were collected in the investigated localities. Abundance and frequency of all species in the samples and in each surveyed biotope are given. The performance of each sampling method has been evaluated, in terms of number of species and individuals, and of species unique to each method.Methods based on direct underwater observation (i.e., visual census) and hand collection provided the largest number of species. Accounts on three remarkable species are given: Calappa tuerkayana, Pachygrapsus transverses, and Percnon gibbesi. This study increases the decapod knowledge of the southern Tyrrhenian sea.