Variation of the bathymetric distribution patterns of the macrobenthic fauna on the continental shelf off Jalisco and Colima, Mexico

Abstract

 The abundance, in terms of number of individuals and biomass, of the invertebrate communities in one sector of the soft-bottom continental shelf off Jalisco and Colima (Mexico) was analyzed. The cruises were carried out during three hydroclimatic seasons, as defined by the surface current patterns. Trawl samples were taken from seven sites along the coastline at four bathymetric levels (20, 40, 60 and 80 m), Abundance in the different bathymetric strata was significantly different, but the overall abundance did not vary significantly between seasons. Two bathymetric distribution patterns were found: the first, during the cruises DEM 1 and DEM II, with warm water, presents the greatest abundance at 60 m; the second, during DEM III, with cold water, a low leve1 of dissolved oxygen and the thermocline close to the surface, presents the greatest abundance at 20 m (biomass) and 40 m (number of individuals). The temperature fluctuation in the depth of maximum abundance during the three cruises was 19-2lºC, which suggests a narrow range of thermal preferente in the demersal invertebrate community.