Pasternak, A.F., E.G. Arashkevich, K. Tande & T. Falkenhaug. (2001). Seasonal changes in feeding, gonad development and lipid stores in Calanus finmarchicus and C. hyperboreus from Malangen, northern Norway. Marine Biology, Berlin 138(6):1141-1152.

100563

Pasternak, A.F., E.G. Arashkevich, K. Tande & T. Falkenhaug

2001

138(6):1141-1152.

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Seasonal dynamics of feeding activity, oil sac volume, gonad development, sex ratio and spawning periods in the two sibling species Calanus ®nmarchicus and C. hyperboreus, the key zooplankton copepod organisms throughout the northern Atlantic waters, were studied simultaneously in Malangen, northern Norway, during 1992. We were also tracing di'erences in surfaceand deep-dwelling components of these populations in terms of oil sac volume and gonad development during the time period when the G 1 is preparing for a subsequent generation (G2 ) or hibernation. The main di'erence in the life cycle strategies of these species is the earlier maturation and spawning of C. hyperboreus. No feeding activity in either of the two species was found in February, but both commenced feeding in March, prior to the spring phytoplankton peak. The larger copepod, C. hyperboreus, had a more intensive energy deposition than C. ®nmarchicus. The period of active feeding was much shorter for the former species, only from March through July in copepodite stages CIV and CV, and even less in females ± March and April. Basically, a similar pattern of seasonal changes in gonad length and lipids was observed in the two species. In June, oil sacs in the surface- and deep-dwelling specimens were about equal, during the rest of the year, lipids in the deep CVs exceeded those in the surface. We propose that as copepods accumulated su5cient lipid reserves, they started to descend, while others, containing less fat, stayed in the upper layers feeding. The mean length of the gonads in the surface-dwelling copepods was consistently less than in their deep counterparts from October to February, so that gonad development at the expense of accumulated reserves during resting stage was con®rmed. C. ®nmarchicus males were found in considerable numbers only in February and March, and were only occasionally found in the upper layers (0±100 m), while adult male C. hyperboreus were present from October to March, but were never found in the surface layers. The di'erences in life cycle timing among the two species are discussed in relation to tradeo's with regard to foraging strategies, generation numbers, bioenergetics and predator avoidance.

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