Fecundity characteristics of Calanus finmarchicus in coastal waters of Eastern Canada

Results of an earlier study of fecundity characteristics of the copepod Calanus finmarchicus from the shelf off Nova Scotia are combined with more recent observations from the Estuary and Gulf of St. Lawrence, where female Calanus are considerably larger. Maximum egg production rates of Lower Estuary females in laboratory experiments were consistent with predictions based on the previously-derived relationship between maximum egg production rates and temperature, in which a culture of Thalassiosira weissflogii was used as the food source. Clutch sizes varied considerably and were significantly related to body size. Within a given body size, clutch sizes were observed to differ by up to a factor of two, possibly associated with differences in food availability or female age. Clutch size of Calanus finmarchicus may represent the interaction between the egg production rate that can be supported by the contemporaneous food conditions and the constraint imposed by the diel spawning cycle. Measurement of in situ egg laying rates in the Scotian Shelf-Gulf of St. Lawrence system indicates that egg production was frequently in the range of maximum values for the ambient temperatures found in surface waters. While spawning is initiated in spring with the vernal increase in primary productivity, it is not tied to later periods of phytoplankton blooms. Once the spring bloom has started, the median egg production rate (5.6% d(-1)) represents, within a factor of two, 85% of spring and summer egg production of C.finmarchicus in the extended shelf system.