CALANUS AND ENVIRONMENT IN THE EASTERN NORTH-ATLANTIC .1. SPATIAL ANDTEMPORAL PATTERNS OF C-FINMARCHICUS AND C-HELGOLANDICUS

Spatial and temporal patterns of Calanus finmarchicus and C. helgoland icus (Copepoda, Calanoida) were investigated in the northeast Atlantic and the North Sea from 1962 to 1992. The seasonal cycle of C. finmarc hicus is characterised by a single peak of abundance in spring, wherea s the seasonal cycle of C. helgolandicus shows 2 abundance maxima, one in spring and one in autumn. The former species mainly occurs in nort hern regions (limited by the 55 degrees N parallel in the North Sea an d by the 50 degrees N parallel in the open ocean). The latter species shows 2 types of spatial patterns, occurring in the Celtic Sea during spring and in the Celtic Sea plus the North Sea in autumn. Differences in seasonal spatial patterns of Calanus species may result from diffe rent responses to the environment, ultimately due to different life cy cle strategies, different vertical distributions, opposite temperature affinities and interspecific competition. Futhermore, results reveal that annual means of abundance are closely related to annual maxima an d to spatial extensions of the species. It also appears that the long- term trends of the 2 Calanus species are opposite: C. finmarchicus sho ws a clear downward trend in abundance, while C. helgolandicus present s an upward one.