Vertical distribution of overwintering Calanus finmarchicus in the NE Norwegian Sea in relation to hydrography

• Published in: Journal of Plankton Research
• Main Authors: Gaardsted, Frank, Tande, Kurt S., Pedersen, Ole-Petter
• Format: Text
• Language: English
• Published: Oxford University Press 2011
• Subjects: Article; Norwegian Sea; Calanus finmarchicus; Copepods
• Online Access: http://plankt.oxfordjournals.org/cgi/content/short/fbr042v1; https://doi.org/10.1093/plankt/fbr042

This study uses Laser Optical Plankton Counter (LOPC) data to study the vertical distribution of the copepod Calanus finmarchicus in relation to hydrography in the NE Norwegian Sea, in January 2009 and January 2010. The high sampling efficiency of the LOPC produced data with higher vertical resolution and allowed a larger number of stations to be sampled in a smaller area compared with previous studies. There were no significant differences between 2009 and 2010 in any of the quantities, median depth, C. finmarchicus layer thickness and temperature and salinity at median depth, indicating that the vertical distributions for the two different years were overall very similar. There was, however, considerable spatial variability in median overwintering depth, and this was strongly correlated with the depth of the overlying Atlantic Water layer. We also observed a significant correlation between C. finmarchicus layer thickness and the mean abundance in the layer, indicating that a vertical stretching and squeezing of the copepod distribution took place in the area. These results suggest that copepods were subject to vertical movement caused by local hydrodynamic variability which is in addition to other vertical motion due to e.g. buoyancy forces. Finally, the results are discussed with respect to future sampling strategies in the area.