DEEP-WATER DECAPOD CRUSTACEAN COMMUNITIES IN THE NORTHWESTERN MEDITERRANEAN - INFLUENCE OF SUBMARINE CANYONS AND SEASON

The specific composition and abundance of bathyal decapods in the Cata lan Sea were investigated. A total of 109 bottom trawls were effected at depths ranging from 141 to 730 m on the continental slope in the Ca talan Sea (northwestern Mediterranean) during two sampling cruises in spring and autumn 1991. Multivariate analysis of the samples revealed four groups of the decapod crustacean communities: (1) A shelf-slope t ransition-zone group at depths between 146 and 296 m, primarily charac terized by the presence of Plesionika heterocarpus; (2) an upper-slope community between 245 and 485 m, characterized by the presence of the mesopelagic species Pasiphaea sivado and Sergestes arcticus, with Pro cessa nouveli, Solenocera membrancea and Nephrops norvegicus as second ary species; (3) a middle-slope community below 514 m, with Aristeus a ntennatus and Calocaris macandreae as the most abundant species; (4) a group at 430 to 515 m, comprising all samples collected exclusively w ithin or in the vicinity of submarine canyons. Mesopelagic decapods we re predominant on the slope, while benthopelagic fishes (Merluccius me rluccius, Micromesistius poutassou, Gadiculus argenteus) replaced meso pelagic decapods on the shelf. There were seasonal variations, with hi gher densities of mesopelagic species in spring, which were probably r elated, among other factors, to variations in the photoperiod. Our sur veys also revealed higher species richness in the canyons together wit h seasonal changes in the megafaunal biomass. Generally, the upper and middle-slope communities both displayed seasonal changes in the compo sition and abundance of megabenthos.