Habitat selection of overwintering Calanus finmarchicus in the NE Norwegian Sea and shelf waters off Northern Norway in 2000–02

Abstract

The abundance and distribution of overwintering Calanus finmarchicus in the NE Norwegian Sea and shelf waters off North Norway was studied during January for 2000–02. Depth integrated distribution of C. finmarchicus CV showed aggregations with high abundances in the Lofoten Basin and southwest of Tromsøflaket for all three years. The exact location of the aggregation areas and the maximum abundances did, however, vary between the years. The concentrations southwest of Tromsøflaket were almost twofold higher in 2000 at 150 000 ind. m−2 compared to 70 000 and 90 000 ind. m−2 in 2001 and 2002, respectively. Vertical distribution of the animals was similar for the three years, with most of the CVs of the population residing in the depth interval between 700 and 1200 m. Peak abundances of 350 ind. m−3 were found at 850–1000 m west of Tromsøflaket in 2000, whereas in 2001 the maximum abundances were located in the Lofoten Basin at 700–900 m, in the order of 150 ind. m−3. In 2002, the highest concentration of animals was found west of Vesterålen between 1100 and 1200 m, with a concentration of 385 ind. m−3. The vertical and horizontal distribution of C. finmarchicus CV closely followed the hydrographic structures in the area, with the highest abundances associated with cold (<2°C), less saline (34.85–34.9) water with a density of 27.95–28. The patches of high abundance were located in confined areas along the continental shelf slope and in the Lofoten Basin, indicating that the animals may have been extracted from the highly flushed surface areas in late summer during their ontogenetic descent, and trapped in mesoscale physical features in the deep‐water masses throughout the winter. We argue that deep‐water mesoscale anticyclonic eddies, which are frequently formed along the continental slope and in the Lofoten Basin, may provide favourable retention areas for the overwintering population of C. finmarchicus. Consequently, the impact of ocean climate as well as more regional and local effects on the creation and persistence of these mesoscale features is likely to influence the Calanus abundance and advection paths in the following spring and summer.

Carbon and nutrient mixed layer dynamics in the Norwegian Sea

“…This distinction is important when considering more than one phytoplankton group because diatoms, dinoflagellates and microzooplankton are the food sources for mesozooplankton; whereas flagellates and E. huxleyi are the food sources for microzooplankton. Furthermore, although mesozooplankton, particularly copepods, have been well studied in the Nordic Seas (Dale et al, 2001;Halvorsen et al, 2003) and it is widely acknowledged that they have an important role in transferring energy to higher levels of the food web, they may be of secondary importance in terms of grazing of phytoplankton, and hence carbon flux, when compared to microzooplankton. There is a lack of microzooplankton grazing studies in the Norwegian Sea, yet reports from other areas suggest that microzooplankton impact significantly on phytoplankton populations (e.g.…”

Shelf recruitment of Calanus finmarchicus off the west coast of Norway: role of physical processes and timing of diapause termination

“…Its life cycle includes overwintering at depth in the deep basins of the Norwegian Sea or in fjords. The copepodites of Stages 4 and 5 descend to their overwintering depth at 400 to 1400 m during summer (Heath et al 2000, Halvorsen et al 2003). Prior to descending, the copepods store fat, and this makes it a particularly nutritious food source.…”

“…Individuals that descend over the shelf will have a shallower overwintering depth and thus suffer a higher predation from visual predators than individuals that overwinter in the deep dark basins and fjords (Bagøien et al 2001). The shelf abundance is therefore low during winter (Halvorsen et al 2003), but is replenished each spring with individuals from outside the shelf. C. finmarchicus do not swim very fast compared to the horizontal currents; thus, shelf recruitment is primarily a result of physical processes (Backhaus et al 1994.…”

Interactions between biological and environmental structures along the coast of northern Norway

“…Mar Ecol Prog Ser 300: [147][148][149][150][151][152][153][154][155][156][157][158] 2005 (Lobel & Robinson 1986, Boehlert et al 1992, Bograd et al 1994, Rodriguez et al 2001, Halvorsen et al 2003 and affect the biological productivity of coastal regions (Rey 1981, Kimura et al 1997, Kasai et al 2002). An eddy can concentrate buoyant passive materials when its secondary circulation converges.…”

“…An eddy can concentrate buoyant passive materials when its secondary circulation converges. This mechanism may aggregate patches of plankton in confined areas and may provide favourable retention areas (Halvorsen et al 2003). A divergent eddy on the other hand may increase primary production due to the upwelling of nutrient-rich deep water to the euphotic surface layer, which may further enhance zooplankton production (Kimura et al 1997, Nakata et al 2000.…”