Modelling the basin-scale demography of Calanus finmarchicus in the north-east Atlantic

In this paper, we report on a coupled physical–biological model describing the spatio-temporal distribution of Calanus finmarchicus over an area of the North Atlantic and Norwegian Sea from 56°N, 30°W to 72°N, 20°E. The model, which explicitly represents all the life-history stages, is implemented in a highly efficient discrete space–time format which permits wide-ranging dynamic exploration and parameter optimization. The underlying hydrodynamic driving functions come from the Hamburg Shelf-Ocean Model (HAMSOM). The spatio-temporal distribution of resources powering development and reproduction is inferred from SeaWiFS sea-surface colour observations. We confront the model with distributional data inferred from continuous plankton recorder observations, overwintering distribution data from a variety of EU, UK national and Canadian programmes which were collated as part of the Trans-Atlantic Study of Calanus (TASC) programme, and high-frequency stage-resolved point time-series obtained as part of the TASC programme. We test two competing hypotheses concerning the control of awakening from diapause and conclude that only a mechanism with characteristics similar to photoperiodic control can explain the test data.