Comparative life histories of three species of planktonic calanoid copepods in Dabob Bay,Washington

The life history patterns of Calanus marshallae Frost, C. pacificus Brodsky, and Metridia lucens Boeck were determined in Dabob Bay, Washington, USA, during 1973 and October 1981–September 1982. C. marshallae emerged from diapause and moulted to adults in January–February. One major generation was observed, having been produced mainly during early to mid-March. Most surviving individuals spawned in March, arrested development at the C5 stage, and were in diapause by late May. However, some individuals developed to adults by late April and produced a very minor second generation. C. pacificus emerged from diapause and moulted to adults in February–March. The first generation produced during the spring lagged slightly behind the C. marshallae generation. C. pacificus produced two additional generations, one in late spring and one in the fall. The production of the three generations coincided with or closely followed phytoplankton blooms. Some C. pacificus arrested development at the C5 stage and entered diapause during the summer, but the majority of the population did not do so until fall. M. lucens did not appear to enter a diapause state. The fall and winter population was chiefly adult females which mostly remained at depth and were reproductively immature. Nevertheless, naupliar M. lucens were found on all sampling dates, indicating that reproduction never ceased as it did for the two Calanus species. M. lucens produced generations in late winter/early spring, late spring, and late summer/early fall. Interspecific comparisons between the life histories observed in Dabob Bay and intraspecific comparisons between the life histories in Dabob Bay and other locations are made. The advantages or disadvantages conferred to the copepods by their differing life histories are also discussed.