The pelagic food web of the Gulf of Maine, which includes herring, sand lance, mackerel, and the North Atlantic right whale, depends heavily on the lipid-rich marine copepod, Calanus finmarchicus. This small crustacean is a keystone species in the Gulf of Maine, providing as much as 77% of the diet of forage fish and anchoring the Gulf of Maine's productivity in many ways. As Henry Bigelow observed in 1924, "the importance of Calanus finmarchicus in the general economy of the Gulf of Maine can not be overestimated."
Jeff Runge and Rebecca Jones of the University of Maine and GMRI have investigated the abundance and distribution patterns of C.finmarchicus to learn more about the drivers that make this species so successful in the Gulf of Maine. Observations taken in the deep waters of Wilkinson Basin reveal an abundance of copepods in the critical fifth developmental stage, which provides lipid-rich energy for the food chain. The Gulf of Maine uniquely benefits from cold-water intrusions originating in the Gulf of St. Lawrence and Labrador Sea and, for now, continues to provide nutrient-rich habitat for these critical copepods and the pelagic species that depend on them. Local conditions, however, do not explain all of the success of C.finmarchicus in the Gulf of Maine. It has been hypothesized that a portion of theC.finmarchicus population may originate in the Bay of Fundy and are carried along the Maine Coastal Current, enhancing local production in Wilkinson Basin.
Researchers have recently observed significant variability in the abundance of C.finmarchicus in inshore waters versus offshore waters, which fishermen may have also observed and scientists do not yet fully understand. Early detection of changes in abundance or sudden shifts from historical trends can yield important insights into the mechanisms sustaining abundance of this sentinel species. Continued monitoring is critical to understand these changes.
Parallel to this research in the Gulf of Maine, French researchers have analyzed C.finmarchicus abundance in relation to sea surface temperatures (SST) from satellite data in the North Atlantic basin and associated coastal shelves. Using climate-ocean models, they predict that the annual mean 10 degree Celsius isotherm in SST (which defines the southern boundary of the subarctic range ofC.finmarchicus) will shift north of the Gulf of Maine by 2050.
It is unclear whether this species will disappear from the Gulf of Maine as these models predict, or continue to be sustained by cold water currents from the North. Any changes in the underlying ecosystem will certainly impact not just C.finmarchicus, but the entire food web that depends on it.
Portland Press Herald:Changing Ecosystem Concerns Fishermen March 9, 2013