Variations in the abundance of Centropages typicus and Calanus helgolandicus in the North Sea:: deviations from close relationships with temperature

The interannual variations in abundance of the calanoid copepod Centropages typicus (Kroyer) in the North Sea are significantly positively correlated with sea-surface temperature. The same is true of Calanus helgolandicus Claus. In both cases there was a deviation from the close relationship with temperature for several years in the early to mid-1980s. Centropages typicus was less abundant than expected from 1981 to 1984, but Calanus helgolandicus recovered from a period of lower than expected abundance from 1980 to 1982, to become more abundant than expected from 1983 to 1987. The difference between the responses of the two species to climate-driven changes in seasonal cycles of phytoplankton is interpreted in relation to their biology. Geographical variations of the interannual variability and seasonal cycles of Centropages typicus in the North Sea are analysed. The centre of the population of this species in the North Sea is in the German and Southern Bights, but the variations in abundance may be partly influenced by advection from areas to the west of Britain.