Phytoplankton biomass and production are strongly seasonal. Zooplankton species are primarily of subarctic affinity and are also highly seasonal. Many of the common copepods overwinter in deep water and have seasonally restricted growing seasons. There are several major estuaries that serve as spawning and nursery grounds for fish. Some pelagic fish spawn in Region I. Region II-Cape Blanco to Point Conception.
Primary production is strongly seasonal, and can be elevated in mesoscale jets and eddies.
Zooplankton biomass varies seasonally. There are a few major estuaries. Region II is the latitudinal minimum in spawning by epipelagic fishes. Region III-Point Conception to Punta. Primary production shows damped seasonal variation, which is often exceeded by interannual variations.