The abundances and distributions of the marine planktonic copepods Calanus marshallae, Calanus pacificus, and Metridia lucens, along with some of the factors controlling them, were investigated in Dabob Bay, a fjord in Washington. C. pacificus copepodids were closely associated with the surface waters, either displaying a normal diel vertical migration (DVM) or being nonmigratory. M. lucens copepodids were less strongly associated with the surface layers and their migration behavior was more varied. Some stages displayed normal DVM, some did not migrate, and others displayed reverse DVM at times. On most dates there were significant portions of all stages of M. lucens in the deepest layers sampled.

The life histories of C. marshallae, C. pacificus, and M. lucens were determined. C. marshallae emerged from diapause and moulted to adults in January and February. One major generation was 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. C. pacificus emerged from diapause and produced its first spring generation slightly after C. marshallae and produced additional generations in the late spring and the fall. By mid-fall the population was dominated by diapausing C5s. M. lucens did not appear to enter a diapause state. The fall and winter populations were chiefly adult females which demonstrated some activity. M. lucens produced generations in late winter/early spring, late spring, and late summer/early fall.

Predation and advection acted to differing degrees on all three populations, changing their abundance cycles from those expected based on the life histories. All three species had major reproductive periods in spring, but only M. lucens consistently increased in abundance at this time. This was likely because the vertical distributions of M. lucens copepodids make them less available to predators and less susceptible to wash-out from the bay. C. pacificus appeared most influenced by predation and advection. Its numbers in fact decreased during spring reproductive periods, but increased dramatically during the fall reproductive period. However, the fall increase appeared largely due to advection of overwintering individuals into the bay.