Testing a new hypothesis on the persistence of Calanus finmarchicus in the Gulf of Maine: Coastal Amplification of Supply and Transport (CAST)

The lipid-rich calanoid copepod, Calanus finmarchicus, plays a critical role in the pelagic food web of the North Atlantic ecosystem. Deep basins along the continental shelf, such as Wilkinson Basin (WB) in the Gulf of Maine, harbor high abundance of diapausing C. finmarchicus during the summer and fall that have persisted despite predictions to the contrary. Identifying the major source of diapausing individuals is critical to the understanding of mechanisms that allow population persistence. This is especially true for a shelf system such as the the Gulf of Maine, which has recently experienced significant warming that could potentially threaten the existence of the population in the region. In this study, we conduct a series of Lagrangian tracking experiments using a copepod life history individual-based model. Model results suggest that coastal waters are the major upstream source for individuals entering dormancy in WB over summertime, although pathways and distribution patterns vary with vertical positioning and release timing of particles. By linking these model results and the observed high springtime egg production rate in the coastal Gulf of Maine, we propose a new mechanism for population persistence that involves coastal amplification of supply (spring reproduction/summer growth in the food-rich coastal region) and transport to receiving basins (e.g. WB) capable of harboring the overwintering stock.