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

The community structure of pelagic copepods was obtained horn 494 zooplankt on samples collected on ten cruises made by CICIMAR in the northwest Mexica n Pacific (31 degrees N 118 degrees W, 22 degrees N 108 degrees W) between 1984 and 1989. Of the 144 taxa identified, Acartia danae (temperature-tropi cal), Calanus pacificus (transitional), Euchaeta marina (tropical), and Ple uromamma abnominalis (tropical) were the must important species according t o their frequency of occurrence, abundance, and contribution to total varia nce of the community. C. pacificus was dominant in almost every month sampl ed. 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. abdomina lis changed month by month and with latitude. The dominance of C. pacifius 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.