Community structure of pelagic copepods in the eastern tropical Pacific Ocean during summer and autumn

The Eastern Tropical Pacific Ocean (ETPO) is a region of interest for commercial fisheries but is subject to high oceanographic variability, which affects primary and secondary production. Because pelagic copepods contribute significantly to secondary productivity, they were investigated to examine community structure variation both temporally and spatially. Zooplankton samples were collected from August to December 2003 using a bongo net (333 um in mesh size). Ninety-six zooplankton samples were analysed, recording 94 copepod species from orders Calanoida, Cyclopoida, Harpacticoida and Poecilostomatoida. The study area could be divided into six geographical zones based on the numerically dominant species. The oceanographic conditions were relatively stable during summer and autumn. Total copepod abundance was higher (47,096 to 62,681 ind.100 m-3) in stations near the coast, mostly in southern Baja California and the Gulf of Tehuantepec; the lowest densities were recorded towards the study area's oceanic regions. Similarly, ecological diversity was higher in zones influenced by tropical mass waters. The biogeographical affinity of copepod species was dominated by tropical species (75.5%), whereas subtropical and temperate species were far less abundant (15.7 and 8.6%, respectively).