On the pelagic copepod community of the central mexican tropical pacific (autumn, 1990)

Abstract

Zooplankton samples were collected during autumn (September, 1990) off the coasts of the Mexican state of Jalisco, northwestern Mexico, in the eastern tropical Pacific. Taxonomic analysis of the pelagic Copepoda yielded 44 species, Subeucalanus subcrassus, Temora discaudata, Undinula vulgaris, Euchaeta marina, Centropages furcatus, and Candacia catula being the overall dominant forms. Together they represented almost 75% of total copepod numbers. The influence of the North Equatorial Current, related to tropical conditions, is clear in the local community structure. Shannon-Wiener diversity was homogeneously high (over 3.2 bits/ind.) in most samples. Highest densities were recorded in the neritic zone. Overall copepod density values suggest a moderate to high productivity in the surveyed area. Station clustering showed a neritic and an oceanic facies, their limits roughly determined by the outer border of the narrow shelf. However, the coast-ocean gradient is moderate, with abundant neritic-oceanic forms, and oceanic representatives over the continental shelf. These effects may result from across-shelf mixing of neritic and oceanic water due to (1) the effect of inshore-wards wind-driven advective processes, and (2) the narrowness of the continental shelf. It is suggested that these processes favour a degree of homogeneity of the copepod community along this and other parts of the Mexican tropical Pacific.