Modeling the interactions between the seasonal and diel migration behaviors of Calanus finmarchicus and the circulation in the Gulf of St. Lawrence (Canada)

The Gulf of St.-Lawrence (GSL) is a dynamic region supporting a productive pelagic ecosystem. This environment presents unique opportunities to study the interactions between the population dynamics of planktonic species and the variability of physical processes. The copepod Calanus finmarchicus is a dominant component of zooplankton biomass and abundance in the GSL. We developed a 3-D coupled physical–biological numerical model in order to study the population dynamics of C. finmarchicus in the GSL for the year 1999. We coupled a life cycle model of C. finmarchicus representing the average properties of the population in terms of egg production, development, migration behavior and mortality to a regional circulation model driven by realistic atmospheric, hydrological and oceanic forcing. The distribution and abundance patterns of C. finmarchicus were sensitive to the migration behavior owing to the strong vertical and horizontal shears in the circulation. Both the timing of seasonal ontogenetic vertical migrations and the diel vertical migrations appeared to be essential to produce simulation results similar to the observations and to ensure the perennial presence of a local population in the GSL.

Research highlights
► 3-D modeling study of C. finmarchicus in the Gulf of St-Lawrence (GSL).
► Stage-based life cycle model of C. finmarchicus coupled to a high-resolution regional circulation model.
► Distribution and abundance patterns of C. finmarchicus sensitive to the migration behavior owing to the strong vertical and horizontal shears in circulation.
► Both the timing of the seasonal ontogenetic and the diel vertical migrations of advanced stages essential to ensure the perennial presence of a local population in the GSL.