Distribution characteristics of pandalid shrimps (Decapoda: Caridea: Pandalidae) along the central Mediterranean Sea.

Abstract: Community structure and faunal composition of decapod crustaceans off the west coast of central Italy (western Mediterranean) were investigated. Samples were collected during five trawl surveys carried out from June 1996 to June 2000 from 16 to 750 m depth. Multivariate analysis revealed the occurrence of five faunistic assemblages: 1) a strictly coastal community over sandy bottoms at depths < 35 m; 2) a middle shelf community over sandy-muddy bottoms at depths between 50 and 100 m; 3) a slope edge community up to 200 in depth as a transition assemblage; 4) an upper slope community at depths between 200 and 450 m, and 5) a middle slope community at depths greater than 450 m. The existence of a shelf-slope edge transition is a characteristic of the western and central Mediterranean where a Leptometra phalangium facies is found in many areas at depths between 120 and 180 m. The brachyuran crab Liocarcinus depurator dominates the shallow muddy-sandy bottoms of the shelf, while Parapenoeus longirostris is the most abundant species from the shelf to the upper slope assemblage. The dominant species on the middle slope are mainly nektobenthic (Aristeus antennatus, Aristaeomorpha foliacea, Plesionika martia), bentho-pelagic (Pasiphaea sivado) and benthic species (Nephrops norvegicus). The average diversity of the five assemblages defined increased with depth and the highest diversity values were found in the slope assemblages. Depth is the main factor influencing decapod assemblage composition, but sediment type and dissolved organic matter seem to be secondary structuring factors particularly in the shelf zone.