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

Abstract

The copepod Calanus finmarchicus is an important part of the Norwegian Sea ecosystem because of its dominating abundance and importance as prey for fish larvae and adult planktivorous fish. The abundance of C. finmarchicus on the Norwegian shelf is generally low in winter, whereas in spring the shelf is replenished by individuals that overwinter at depth, either in fjords or in the deep basins of the Norwegian Sea. In the present study shelf recruitment is investigated using an individual-based model for C. finmarchicus coupled to the HYbrid Coordinate Ocean Model and a biophysical model. The model was set up on a nested grid along the west coast of Norway and used to study the shelf recruitment originating from the Norwegian Sea. We investigate the effect of wind, currents and the timing of Calanus ascent on the shelf abundance of C. finmarchicus. The most important findings are the following: (1) periods of large on-shelf transport are connected with strong westerly winds associated with passing low-pressure systems; (2) the transport of overwintering adults onto the shelf determines the total shelf abundance prior to mid-summer; (3) the early spring bloom on the shelf causes increased shelf population of C. finmarchicus in the spring and throughout the summer compared to the areas further off-shore; and (4) the entry routes taken by C. finmarchicus are related to bathymetry; in particular, the deep trenches around Halten Bank and the Norwegian trench are favoured places to enter the Norwegian shelf. © Inter-Research 2009.