On the pelagic Copepod community of the central Mexican tropical Pacific (Autumn, 1990)

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 sp ecies, Subeucalanus subcrassus, Temora discaudata, Undinula vulgaris, Eucha eta marina, Centropages furcatus, and Candacia catula being the overall dom inant forms. Together they represented almost 75% of total copepod numbers. The influence of the North Equatorial Current, related to tropical conditi ons, is clear in the local community structure. Shannon-Wiener diversity wa s homogeneously high (over 3.2 bits/ind.) in most samples. Highest densitie s were recorded in the neritic zone. Overall copepod density values suggest a moderate to high productivity in the surveyed area. Station clustering s howed a neritic and an oceanic facies, their limits roughly determined by t he outer border of the narrow shelf. However, the coast-ocean gradient is m oderate, with abundant neritic-oceanic forms, and oceanic representatives o ver the continental shelf. These effects may result from across-shelf mixin g 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 th e copepod community along this and other parts of the Mexican tropical Paci fic.