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

Abstract

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 67°00′N, 13°55′W to 68°00′N, 12°40′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 (~5°C, mean for uppermost 50 m). Below 75 m, temperature remained at <0°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 (~1 mg Chl a m⁻³). Calanus finmarchicus dominated in terms of numbers (~75%), while C. hyperboreus dominated biomass (~76%). Calanus glacialis occurred only in low numbers (~1%) and was only a small portion of biomass (~0.7%). The abundance of all species was low during the winter and peaked once during summer: C. finmarchicus in July (~16 000 ind. m⁻²) and C. glacialis and C. hyperboreus in June (~370 and ~7700 ind. m⁻², respectively). The biomass of C. finmarchicus had two maxima, in April (~1.9 g m⁻²) and July (~1.5 g m⁻²), while C. hyperboreus peaked in June (~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.