Seasonality in surface-layer net zooplankton communities in Prince William Sound, Alaska

The upper-layer net-zooplankton community in Prince William Sound, Alaska, is characterized by strong seasonality. Abundance and wet-weight biomass in the upper 50 m drop to fewer than 100 individuals and 10 mg m(-3) in February before rebounding to 5000 individuals and 600 mg m(-3) in June. Copepods dominate in all months, but are augmented by other prominent taxa, particularly pteropods and larvaceans during the late spring, summer and fall. The small copepods Pseudocalanus, Acartia and Oithona are common. Though much less abundant, larger calanoids like Neocalanus, Calanus and Metridia contribute substantially to the biomass in spring and early summer. Meroplankters like barnacle nauplii are also occasionally very abundant. Neocalanus, Calanus and Pseudocalanus all exhibit ontogenetic vertical displacement of populations when stage 5 copepodites (C5) leave the surface in late May and early June for deep water. This seasonality has implications for food-webs supporting juvenile pink salmon (Oncorhynchus gorbuscha) and Pacific herring (Clupea pallasi) in Prince William Sound.