Climate variability and possible effects on arctic food chains: The role of Calanus

Abstract

The large oscillations of abiotic factors in the Arctic is critical in structuring its marine biota and the biodiversity of its indigenous populations and communities. The seasonal light cycle is modified by the sea ice cover, creating a situation dominated by phytoplankton blooms, that follow the receding ice edge, and in leads as the sea ice opens during the Arctic summer (Sakshaug 1997, 2003; Hegseth 1998; Falk-Petersen et al. 2000a; Engelsen et al. 2002). Blooms of phytoplankton propagate through Arctic waters (Zenkevich 1963) and carbon fixed through photosynthesis is rapidly converted into large, specialised lipid (marine fat) stores by the herbivorous Calanus species (Lee 1975; Sargent and Henderson 1986). These high-energy lipids are then rapidly transferred upwards through the food chain in large amounts (Falk-Petersen et al. 1990). The increase in lipid level from 10-20% of dry mass in phytoplankton to 50 - 70% in herbivorous zooplankton is probably one of the most fundamental specialisations in polar bioproduction. The lipid - based energy flux is one of the primary reasons for the large stocks of fish and mammals in Arctic waters. The importance of the diatom => Calanus food chain in the Arctic pelagic food has been demonstrated by Falk-Petersen et al. (1986; 2002) and Scott et al. (2002). A wide spectrum of predators from zooplankton to fish and sea birds has also been analysed by using fatty acid trophic markers in Arctic waters. In all of these studies the Calanus C20 and C22 lipid trophic markers were strikingly dominant, demonstrating the importance of the Calanus species in the Arctic pelagic ecosystem (Falk-Petersen et al. 2001, 2002, 2004; Dahl et al. 2003. The population size spectrum and energy content of the key Calanus species, being potential prey for zooplankton-eating fish and sea birds, is therefore instrumental in structuring the biodiversity of Arctic ecosystems. We believe that understanding the climate variability is a key to understand the biology of Arctic animals and the biodiversity of Arctic systems. In this paper we discuss how different climate regimes in the Nordic Seas can influence Calanus- based Arctic food chains.