Award: OCE-1235920

The planktonic copepod, Calanus finmarchicus, is a dominant member of the zooplankton across the North Atlantic Ocean. In the northwest Atlantic, the southern edge of its reproductively active range is the Gulf of Maine. Despite its location at the southern boundary, the Gulf of Maine harbors extremely abundant concentrations of C. finmarchicus, which plays a fundamental role in the regionÆs marine ecosystem. Of particular importance to predators and to the regionÆs fishing economy are the lipid-rich (with fatty acids), late preadult stages (CIV-CV) that dominate the zooplankton biomass in late spring and summer. These stages serve as a primary source of energy either directly (northern right whales) or indirectly (via consumption by primary consumers such as herring, mackerel and sandlance) for the ecosystemÆs top predators, including groundfish, tuna, marine mammals, many seabirds and even lobsters. Over the past decade, sea surface temperature (SST) in the Gulf of Maine has warmed at a rate (0.2°C yr-1) that is more than ten times greater than the 100 yr rate. In 2012, a record warm year, SST in summer was as much as 5°C higher than the long term average. The mean annual SST has exceeded 10°C in the western Gulf of Maine since 2006 and in the eastern Gulf of Maine since 2012.. This temperature landmark has ecological significance as a biogeographic transition zone in the North Atlantic. Statistical-based modeling of C. finmarchicus habitat, for which SST is an important variable, combined with forecasts with an atmosphere-ocean climate model predict that climate driven ocean warming will force distribution of the species northward out of the Gulf of Maine over the next several decades. Because zooplankton diversity in the Gulf of Maine is low and there is no other obvious candidate to replace the production of energy rich lipids for higher trophic levels, significant declines or fluctuations in the abundance of C. finmarchicus will likely have important implications for management of the regions resources and social and economic adaptation to environmental change. This research, funded under the NSF RAPID program designed to support quick-response research to significant and unanticipated events, investigated the population response of C.finmarchicus to record warming in the Gulf of Maine in 2012. Population data from two time series stations and a plankton survey conducted in the Gulf of Maine in early autumn, 2012, showed that C. finmarchicus abundance in the western Gulf of Maine was within the normal range and did not show signs of decline. On the contrary, a new cohort, likely originating from early egg production during a winter phytoplankton bloom in early spring, 2013, was the most abundant ever recorded in the eight-years for which there are time series data. To explain why C. finmarchicus persists in the Gulf of Maine despite the recent warming trend, a new hypothesis that implicates transport in currents from colder waters in the Gulf of St. Lawrence and Nova Scotia Shelf, where the species is abundant as well transport of C. finmarchicus in the Maine Coastal Current, a relatively cold, southwesterly flowing current along the coast of the Gulf of Maine. In contrast to the central Gulf of Maine, the Maine Coastal Current is rich in phytoplankton throughout the summer months, providing a source of food for the species to reproduce and grow. These individuals that grow up and become filled with fat during the late spring and summer are delivered by the Maine Coastal Current to the southern and western parts of the Gulf of Maine, where they spend the winter in diapause. Recognizing the importance of C. finmarchicus, the Northeast Regional Association of Coastal and Ocean Observing Systems (NERACOOS) and the Northeast Region Ocean Council (NROC), two regional associations of representing federal and state agencies as well as universities and non-profit organizations, have identified it as a k...