Seasonal development of Calanus finmarchicus along an inshore-offshore gradient southwest of Iceland

The abundance and development of the copepod Calanus finmarchichus southwest of Iceland was studied in relation to phytoplankton biomass at three stations along a hydrographic gradient during the period February-November 1991. Following increasing stratification nearshore during April, the phytoplankton spring bloom began in the shallow area and culminated in April-May. At greater distances from the shore the stratification did not start until the middle of May and consequently the blooming began later in the deep offshore areas, probably culminating during mid to late May. The number of Calanus finmarchicus was low during the winter months and peaked twice during the summer at all three stations (May-June and July-September), reflecting the two generations of C. finmarchicus which grew up in both shallow and deep water southwest of Iceland. In both waters the spawning of the overwintered generation appeared to begin before the observed phytoplankton spring bloom. However, peak spawning of the overwintered generation approximately coincided with the phytoplankton spring bloom, while also occurring earlier nearshore (April) than farther out from the shore (May). At all three stations there was a second generation of C. finmarchicus which also hatched earlier nearshore (June) than more distant from land (June-July).