Key species in the pelagic copepod community structure on the west coast of Baja California, Mexico

The community structure of pelagic copepods was obtained from 494 zooplankton samples collected on ten cruises made by CICIMAR in the northwest Mexican Pacific (31°N 118°W, 22°N 108°W) between 1984 and 1989. Of the 144 taxa identified, Acartia danae (temperate-tropical), Calanus pacificus (transitional), Euchaeta marina (tropical), and Pleuromamma abdominalis (tropical) were the most important species according to their frequency of occurrence, abundance, and contribution to total variance of the community. C. pacificus was dominant in almost every month sampled. The ratio of the abundance of this species to the other three decreased from north to south. The abundance of A. danae, E. marina, and P. abdominalis changed month by month and with latitude. The dominance of C. pacificus over the other species suggests resource partitioning favoring this species. The abundance of the two tropical species increased in summer and autumn, and that of the transitional species in winter and spring.