Growth of Calanus finmarchicus on Georges Bank

R. G. Campbell, E. G. Durbin, and J. A. Runge

Growth and molting rates of Calanus finmarchicus were measured in shipboard incubations on Georges Bank during 1994, 1995, 1997, and 1999 as part of the US GLOBEC NW Atlantic / Georges Bank program. Molting rates of copepodite stages were highly variable and not related to chlorophyll a, but increased with temperature within a stage. However, molting rates of naupliar stages were positively correlated with both temperature and chlorophyll a. Growth rates of copepodite stages were not related to temperature, but there was a weak positive correlation with chlorophyll a. When copepods were food limited, growth rates could be enhanced by enriching the ambient water with a mixed phytoplankton culture while molting rates were unchanged, which suggested that molting was not as tightly coupled to food as growth.

During April on the southern flank of the Bank, there were periods when food limitation was severe. This was especially true during April 1997. These episodes of food limitation may in part be responsible for the patterns in abundance and stage distribution of Calanus observed on the Bank. Food limitation may be partially responsible for the low numbers of Calanus nauplii on the southern flank of the Bank in May observed most years during zooplankton broadscale surveys. However, on the crest of the Bank where Calanus nauplii are low in abundance during most of the winter / spring period, predation and / or advective processes appear to be more important in controlling these patterns because we did not find evidence that food limitation was important.