GULF OF MAINE COPEPOD PRIMER
During any given season, over 80% of the total zooplankton abundance in the Georges Bank area of the Gulf of Maine is accounted for by just six copepod species. These are: Calanus finmarchicus, Pseudocalanus sp., Paracalanus parvus, Centropages typicus, C. hamatus, and Oithona similis.

Calanus finmarchicus and Pseudocalanus sp. are the numerically dominant species in the early spring to early summer faunal assemblage, while Paracalanus parvus and the two Centropages species dominate the zooplankton community in the late summer and fall. Oithona similis is common throughout the year.



Due to its large (>3 mm as adults) size, the copepod Calanus finmarchicus is the most important contributor to the annual zooplankton biomass cycle, even though it is not the most abundant species numerically. The annual spring/early summer peak in Georges Bank zooplankton biomass depicted in the accompanying figure is primarily due to the presence of C. finmarchicus. The dominance of the species in this system led pioneering oceanographer and Woods Hole founder Henry Bigelow to describe the Georges Bank ecosystem as a "Calanus community."

Calanus, Centropages, and other planktonic copepods are important grazers of diatoms and other large (>20 µm) phytoplankton, linking these primary producers with higher trophic levels in mesopelagic food webs. But these species also function as carnivores, consuming ciliate protozoans and other microzooplankton when such prey items are abundant. For example, C. finmarchicus may derive 20% of its carbon intake from protozoans when they are numerous in the spring, compared to just 5% when prey numbers decline in late summer.

Calanus finmarchicus Life History

The importance of Calanus finmarchicus species to the ecology of the Gulf of Maine warrants a closer look at its life history.

This copepod is ubiquitous in coastal and open ocean midwater environments of the northern hemisphere. In the Atlantic Ocean in winter, the species can be found from the Arctic Ocean south to Chesapeake Bay.

Like all free-living copepod species, Calanus individuals hatch from eggs and proceed through several naupliar and copepodid stages before they become adults. In the Gulf of Maine region, either one (Georges Bank) or two (Gulf of Maine proper) generations are produced between March and July.

The life cycle of Calanus exhibits an interesting twist, in that the final copepodid stage (C5) can enter a state of diapause. Diapause is a period of delayed development or growth and reduced metabolism. This phase provides a mechanism for surviving adverse environmental conditions.

Most Calanus finmarchicus that enter diapause in the Gulf of Maine migrate to deep(300-400 m) basin habitats prior to the onset of the warmest months of late summer. They remain there through the fall and winter, molting into adults by early spring and then migrating vertically to feed in the phytoplankton-rich upper water layers. Large numbers of newly emerged adult C. finmarchicus are also transported into the Gulf of Maine each spring with cold oceanic currents that flow into the Gulf, both through the deep Northeast Channel and in shallower currents that flow across Browns Bank.

The animated seasonal progression shown below graphically depicts the numbers of C. finmarchicus of all age classes collected throughout the Gulf of Maine over the course of many years. The sampling was conducted as part of the U.S. GLOBEC Geroges Banks Program. Note that in the winter months, only the deep Basin habitats of the Gulf of Maine contain large numbers of animals, all of which occur at that time as diapausing C5 copepodids.


Note: Much of the information contained on this page has been adapted from the following sources:

"From Cape Cod to the Bay of Fundy: An Environmental Atlas of the Gulf of Maine" (P.W. Conkling, ed.)
1995 MIT Press.

Bourne, D.W. Zoology and Secondary Production. pp 252-255 in: "Georges Bank" (R.H. Backus and D.W. Bourne, eds.). 1987 MIT Press.

Davis, C.S. Zooplankton Live Cycles. pp 256-267 in: "Georges Bank" (R.H. Backus and D.W. Bourne, eds.). 1987 MIT Press.

Gifford, D.J. 1993. Planktonic protozoa in the copepod diet: Examples from the North Atlantic and North Pacific. ICES Council Meeting Papers, ICES, Copenhagen, Denmark. 15 p.

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