Comparative analysis of Calanus finmarchicus demography at locations around the Northeast Atlantic

Standardized time-series sampling was carried out throughout 1997 at seven locations around the Northeast Atlantic to investigate regional variations in the seasonal demography of Calanus finmarchicus. Sites ranged from an inshore location in the North Sea. where C. finmarchicus formed only a small component of the zooplankton (< 10 mgC m(-2) during spring and early summer). to the shelf south of Iceland. and Weathership M in the Norwegian Sea. where the species dominated the zooplankton (> 2000 mgC m(-2) during spring and summer). The internal consistency of the demographic time-series from each site was investigated by three partial models of life-cycle processes. In general. the demography of late copepodites could be accounted for by a relatively simple forecast model of stage development and diapause. However. there M as a large discrepancy between nowcast estimates of egg production based on female abundance. temperature. and chlorophyll. and hindcast simulations of the egg production required to account for the observed abundance of early copepodite stages. The results point to a gap in our understanding of seasonal variations in rates of egg production and/or survival of nauplii. Overall. the population sampled at Weathership M appeared to be reasonably self-contained, but all other sites were reliant on invasion of overwintered stock in spring. At least two generations were observed at all but one site, but the extent to which these were generated by discrete bursts of egg production varied between sites and seemed to be partly dependent on the proximity to an overwintering location.