Why does a component of Calanus finmarchicus stay in the surface waters during the overwintering period in high latitudes?

• Published in: ICES Journal of Marine Science
• Main Authors: Pedersen, G., Tande, K., Ottesen, G. O.
• Format: Text
• Language: English
• Published: Oxford University Press 1995
• Subjects: Articles; Barents Sea; Norway; Calanus finmarchicus; North Norway
• Online Access: http://icesjms.oxfordjournals.org/cgi/content/short/52/3-4/523; https://doi.org/10.1016/1054-3139(95)80066-2

During the overwintering period Calanus finmarchicus is known to reside in deeper waters in high-latitude environments. More recent data indicate that the overwintering stages of this species are also found in surface water during the winter period. The present article documents that overwintering stages CIV and CV are abundant in the uppermost 100 m at selected sites in the western part of the Barents Sea, and in coastal-and fjord areas in North Norway. The moulting cycle of the surface and deep-water dwelling population components was studied by using a method for monitoring the formation of the opal teeth on the mandibular gnathobase. Although only a limited number of specimens were examined, no moulting indices were found out of approximately 300 specimens examined from November to January. The overall daytime vertical distribution pattern in Grøtsund appeared to have a fairly large component of the population in the uppermost 100 m of depth during the entire winter period, differing from the Barents Sea, where a higher degree of variability in the vertical distribution of C. finmarchicus was found. Physical conditions and trade-offs due to differences in the degree of diapause might account for this vertical distribution pattern. In Grøtsund, the apolysis in stages CIV and CV was found at the beginning of February, prior to the onset of ecdysis. The present study indicated that apolysis in overwintering generations is more closely coupled to ecdysis than shown earlier in C. finmarchicus from the Gulf of Maine.