Factors controlling the seasonal abundance and distribution of Calanus finmarchicus in the Gulf of Maine/Georges Bank region

Calanus finmarchicus, a kind of marine zooplankton, plays an important ecological role throughout the North Atlantic. Striking seasonal variations exist in its abundance and distribution in the Gulf of Maine/Georges Bank region. On the Bank in particular, it represents the dominant portion of the zooplankton in winter-spring and is virtually absent at all other times. During the time of its peak abundance, C. finmarchicus serves as a major food source for the endangered North Atlantic Right Whale and the larvae of the commercial fish, cod and haddock. Insight into what factors control the observed seasonal variations will improve our understanding of the animal's ecology and the processes affecting food availability for its predators.; This work used physical-biological modeling to study how physical transport, behavior and population dynamics can interact to produce the observed seasonal changes in Calanus finmarchicus, on Georges Bank.; Simulations indicate that physical transport of late-stage copepodites from the Gulf of Maine controls the occurence of adults on the Bank in winter-spring, providing a continual supply of C. finmarchicus to the Northeast Peak (NEP) fish spawning grounds. The abundance of female Calanus on the NEP is increased by the interaction of surface-seeking behaviour and seasonal circulation. Physical transport limits the supply of animals to the Bank Crest by geographical source region and season. Surface-seeking behavior increases the number transported there in winter, but cannot overcome the spatial/temporal constraints imposed by the physics. Changes in transport to and from the Crest do not account for the development of the “ Calanus hole” in May–June; predation is the likely controlling factor. Physical transport, timing of seasonal migration and generation time are important controls for the spring aggregations of copepodites in the Right Whale feeding grounds; the Gulf, more than the Bank, is indicated as the source. Different life stages are controlled by different physical and biological factors. Food-limitation severely limits the recruitment of the first generation. Food effects are more important controls than are temperature or behavior, especially for the early-life stages that serve as food for larval fish.