Composition, abundance and distribution of Pteropoda (Mollusca: Gastropoda) on the neritic zone, at the southern Gulf of Mexico (August, 1995)

Abstract

The composition, distribution, and abundance of pteropods were analyzed in relation to hydrographic conditions of the water column (0 to 105 m) in the Gulf of Mexico. Up to 95 samples of zooplankton were collected during August 1995 at 28 stations arranged in five transects on the continental shelf off the main lagoonal systems in the southern Gulf of Mexico, from the Coatzacoalcos River inlet to Paso Real inlet of Términos lagoon . Samples were collected at five depth ranges. Three of the identified taxa constituted 90% of the total pteropod abundance: Creseis acicula f. acicula (72.7%), C. acicula f clava (8.2%), and Limacina trochiformis (9.3%). The highest density of the group occurred within the first 18 m, but 19 of the 39 groups registered were absent from the surface layer (0-6 m), and others had low densities. The results of a CCA suggest that not one parameter by itself determines the distribution of these organisms in the water column, but the habitat of the species does. Species with tropical/subtropical and coastal affinities were the most abundant and occurred mainly in the surface layer, while the oceanic forms were less abundant and occurred mainly in the deep layers probably resulting from the inflow of oceanic water toward the shelf at its deepest layers.