Seasonal variations in abundance, development and vertical distribution of Calanus finmarchicus, C-hyperboreus and C-glacialis in the East Icelandic Current

The seasonal variation in abundance and development of Calanus finmarchicus, Calanus hyperboreus and Calanus glacialis in relation to hydrography and chlorophyll (Chl) a was studied in the Arctic waters of the East Icelandic Current to the north-east of Iceland from March 1995 to February 1996. The sampling was carried out at approximately monthly intervals on a transect of five stations extending from 67degrees00'N, 13degrees55'W to 68degrees00'N, 12degrees40'W. In April, May and June, vertical distribution was also investigated. Spring warming of the surface waters began in May, with maximum temperatures recorded in August (similar to5degreesC, mean for uppermost 50 m). Below 75 m, temperature remained at <0 degrees C throughout the year. The spring bloom of phytoplankton started in early May and the highest Chl a concentrations were measured during late May to early June (similar to 1 mg Chl a m(-3)). Calanus finmarchicus dominated in terms of numbers (similar to 75%), while C. hyperboreus dominated biomass (similar to 76%). Calanus glacialis occurred only in low numbers (similar to 1%) and was only a small portion of biomass (similar to 0.7%). The abundance of all species was low during the winter and peaked once during summer: C. finmarchicus in July (similar to 16 000 ind. m(-2)) and C. glacialis and C. hyperboreus in June (similar to 370 and similar to 7700 ind. m(-2), respectively). The biomass of C. finmarchicus had two maxima, in April (similar to 1.9 g m(-2)) and July (similar to 1.5 g m(-2)), while C. hyperboreus peaked in June (similar to 12.3 g m(-2)). Calanus finmarchicus was estimated to spawn in early May at about the start of the spring bloom, while C. hyperboreus spawned prior to the spring bloom, in late February to early March. On the basis of copepod stage distribution, C. finmarchicus was considered to have a 1-year life cycle and C. hyperboreus at least a 2-year life cycle.