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Seasonal abundances of euthecosomatous pteropods and heteropods from waters overlying San Pedro Basin, California

2003; California Malacozoological Society; Volume: 46; Issue: 4 Linguagem: Inglês

0042-3211

Frances A. Cummings, Roger R. Seapy,

Ocean Acidification Effects and Responses

Ten species of euthecosomatous pteropods and five heteropod species were recorded from replicated oblique plankton tows to a target depth of 300 m taken with an open, 2 m diameter ring net (3 m 2 mouth opening) during 13 monthly cruises from April 1989 to April 1990 in San Pedro Basin, California. Six species of euthecosomes and one atlantid heteropod species were sufficiently numerous in the samples to allow assessment of seasonal patterns. The most abundant euthecosome (Limacina helicina) and heteropod (Atlanta californiensis) are epipelagic species that belong to the Transitional Faunal Province in the North Pacific. The highest densities of both species occurred during the summer, coinciding with the strongest seasonal flow of the California Current and Southern California Eddy. Conversely, during the winter when flow of these currents was weakest, the lowest densities of these species were recorded. Three euthecosome species (Creneis virgula, Limacina bulimoides, and Cavolinia inflexa) are warm water (tropical and subtropical) epipelagic species, although the latter two are most abundant in Central waters. Whereas C. inflexa showed no pattern of seasonal abundance, C. virgula and L. bulimoides had increased densities in the summer, corresponding to the time of maximal Southern California Countercurrent flow. Lastly, two euthecosome species (Limacina inflata and Clio pyramidata) are warm water, mesopelagic species that undergo nocturnal vertical migration into epipelagic waters. Maximal densities of L. inflata were recorded during the winter, which corresponds to a secondary peak in flow strength of the California Current and surfacing of the California Undercurrent. There was no seasonal pattern of abundance for C. pyramidata.