Mullin, M.M. (1993). Reproduction by the oceanic copepod Rhincalanus nasutus off southern California, compared to that of Calanus pacificus. California Cooperative Oceanic Fisheries Investigations (CALCOFI) Reports 34:89-103.

104443

Mullin, M.M.

1993

34:89-103.

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Measuring zooplankters’ rate of egg production can provide estimates of secondary production and of the availability of food for many larval fish. Su- perficially, Rhincalanus nasutus and Calanus pacijicus have similar ecologies; conditions for successful rearing in the laboratory are similar, as are rates of egg production when females are held in the labo- ratory with excess food; also, the abundances of the two species are positively correlated through space and time. Rates of egg production by these two species in the southern California sector of the Cal- ifornia Current were measured in the winters and springs of 1991-93 by holding females in the ambient seawater and in seawater enriched with phytoplanktonic food. At many locations, female Calanus produced eggs when in the unenriched sea- water; they almost always did so when food was enhanced with cultured phytoplankton. In contrast, Rhincalanus seldom produced more than 10 eggs. (female.day) except when incubated with excess food for 2 days, and even then, the spatial/temporal patterns of egg production differed from those of Calanus. Future work should focus on whether there are conditions (season, food, etc.) permitting high reproductive rates in Rhincalanus feeding on the natural seston off southern California; i.e., >10 eggs-(female-day-)I .

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