COMPOSITION AND STRUCTURE OF THE BRACHYURA CRUSTACEAN ASSEMBLAGE ON THE CONTINENTAL SHELF OF LA GUAIJIRA COLOMBIA: RELATION TO DEPTH AND SEDIMENT COMPOSITION

Abstract

Brachyura crustaceans composition and structure assemblage along be continental shelf of La Guajira and its variation according to depth gradient and sediment characteristics were determined. 44 bottom drag samples were taken at 10 and 50 m depth using a semi globe demersal net, during March and April 2005. 83 species belonging to 21 families were identified; the most important families due to their abundance of specimens and amount of species were Goneplacidae, Portunidae, and Mithracidae; and dominant species were Glyptoplax smithii, with, 12.53 % of total abundance; Portunus spinicarpus, 7.42 % and Nemausa cornuta, 6.84 %. The non-metric multidimensional scaling analysis (NMDS) did not show any well defined sampling station clusters, but meaningful statistical differences were found in the assemblage structure according to depth gradient and the different kinds of sediments. The ANOSIM tests and the ordination analysis (NMDS) pointed out that there is a single assemblage that varies gradually with depth, and to a lesser degree by physical sediments characteristics. The ordination (NMDS) also reveals that the assemblage is more heterogeneous at 10 m than at 50 m depth, possibly as a result of the larger environmental variability close to the coast, in comparison with the environmental stability that characterizes deeper zones.