A study of seasonal variations in the pattern of year-to-year changes, for 1948 to 1982, in the abundance of four zooplankton taxa (Pseudocalanus elongatus, Acartia clausi, Calanus finmarchicus and Hyperiidea) for the North Sea suggests that an element of the variations, represented at least in part by a quasi-linear downward trend, has its origins in winter and its occurrence through the year is a function of inherent persistence. A downward linear trend is the dominant pattern in the annual fluctuations in abundance of many species of zooplankton throughout the north-east Atlantic and the North Sea. It is argued that it is reasonable to extrapolate from the limited data set included in the detailed study and to assume a winter origin for the pattern wherever it occurs. Some implications for ideas about the dynamics of the plankton ecosystem are considered. |
