Growth of Calanus finmarchicus nauplii in source and on-Bank waters of Georges Bank

D. J. Gifford, M. E. Sieracki, and J. R. Merrell

Calanus finmarchicus is expatriate on Georges Bank. Populations do not overwinter and must be recruited from off-Bank source waters each spring. We hypothesized that naupliar growth rates would be higher in productive on-Bank waters compared to less productive source waters in regions adjacent to the Bank. Growth rates of laboratory-reared nauplii were measured in experiments done in 3 source regions (Georges Basin, Great South Channel, Scotian Shelf overflow) and 3 on-Bank regions (Bank Crest, Northeast Peak, Southern Flank) during April and May 1997. Laboratory-reared nauplii were incubated in microplankton assemblages from the various source and on-Bank regions. Nauplii were harvested and preserved at the beginning of each experiment and after 48 h incubation. Naupliar volume was determined from optical sections which were created microscopically using differential interference optics and image analysis. Contrary to expectation, growth rate (as increase in biovolume) was higher in source waters than in on-Bank waters in both April and May. The highest growth rates (>100% increase in biovolume/d) were observed in the Scotian Shelf overflow in both months. There was no statistically significant relationship between growth rate and the standing stock of chlorophyll.