Annual weather variability and its influence on the population dynamics ofCalanus finmarchicus

The reaction of the population of Calanus finmarchicus to relatively extrem e annual cycles of weather in the North Sea was investigated by one-dimensi onal model simulations. A population dynamics model for C. finmarchicus was coupled with a physical and a biological upper-layer model for phosphate, phytoplankton and detritus to simulate the development of the successive st ages of C. finmarchicus. Observed annual weather cycles were used to drive the physical water column model, the results of which were then input to th e plankton model. The simulations yielded the temporal development of all s tages of C. finmarchicus over an annual cycle in terms of numbers and weigh ts. Compared with the results reported for 1984 by Carlotti and Radach (199 6; Limnol. Oceanogr. 41: 522-539), it appears that the temporal range for t he occurrence of the peak concentration of C. finmarchicus may be 2 weeks i n the northern North Sea. The simulated variability is in accordance with o bservations. Years with more continuous primary production such as the year 1984, which was cloudy and windy during the summer, may then provide the o ptimum conditions with respect to producing an abundance of zooplankton dur ing the following year.