Seasonal lipid storage as overwintering strategy of Antarctic krill

Abstract

ABSTRACT. Conflicting hypotheses prevail on the overwintering strategies of the Antarctic krill Euphausia superba due to the difficult accessibility of Antarctic waters, especially in winter. and hence, to the lack of seasonal data. This study reports on the seasonal lipid dynam~cs of E. superba (25 to 56 mm) collected In the Weddell Sea in late winter/spring, summer, autumn and mid-winter Total hpid data provide evidence of large seasonal accumulation of reserve lipids in austral summer with a mean lipid content of 28.2 % of dry mass and particularly in autumn, when mean lipid levels peak with 39.2% of dry mass. After the overwintering period mean lipid contents decrease to a minlmum of 10.5% of dry mass, indicating extensive utilisation of lipid reserves during winter. These data suggest that lipids contribute significantly to the overwintenng success of this extremely versatile species. Lipid class analyses of spring and summer specimens (10 to 56 mm) from the Antarctic Peninsula and the Weddell Sea revealed that not only triacylglycerol, but also phosphatidylcholine may serve as important storage lipids of E. superba. In the other dominant Antarctic krill species, E. crystallorophias ( l 0 to 40 mm) and Thysanoessa macrura (10 to 27 mm), wax esters are the primary depot lipid, but phosphatidylcholine also functions as a storage lipid in these species. Phosphatidylcholine is unusual as a reserve lipid, being an essential component of biomembranes. In contrast, phosphatidylethanolamine, the other major phospholipid class, seems to have exclusively membrane functions, since it does not increase (in percent of dry mass) with increasing lipid levels in these 3 euphausiid species.

Changes in lipid composition of the Antarctic krill Euphausia superba in the Indian sector of the Antarctic Ocean:influence of geographical location, sexual maturity stage and distribution among organs

“…Since the early work of Ellingsen (1982), the covariation of PC and total lipids in euphausiids has been confirmed by several studies (Saether et al 1985, 1986, Hagen 1988, Hagen et al 1996, Mayzaud 1997. Seather et al (1986) assumed that both neutral and polar lipids are laid down and utilized when krill lipid reserves are accumulated or depleted.…”

“…Reports by Elligsen (1982), Saether et al (1986), Hagen (1988), and Hagen et al (1996) suggested that polar lipids, and more specifically phosphatidyl choline (PC), may also serve as storage lipids. The involvement of cell structural components as an energy source has been reported for PC as a source of essential polyunsaturated fatty acids in fish for egg and larval development (see Fraser et al 1988).…”

“…In krill the 2 major energy utilizing events are summer reproduction and winter survival under low phytoplankton conditions. Knll store significant amounts of lipids (Clarke 1984, Hagen et al 1996, although most studies have concluded that the concentrations are not sufficient to meet the energy requirements during the winter, when food supply is low (Quetin & Ross 1991, Quetin et al 1994. However, the contribution of lipids to the overall survival strategy of 0 Inter-Research 1998 Resale of full article not permitted krill appears quite s~gnificant (Hagen et al 1996) and, during the summer period, is channeled mainly into reproductive output.…”

“…The role of lipids in Antarctic krill has been the concern of several papers in relation to reproduction (Clark 1980, Kolokowska 1991, Pond et al 1995, Virtue et al 1996, energy storage for overwintering (Quetin & Ross 1991. Hagen et al 1996 and trophlc interactions (Bottino 1974, Reinhardt & Van Vleet 1986, Virtue et al 1993a.…”

“…Hagen et al 1996 and trophlc interactions (Bottino 1974, Reinhardt & Van Vleet 1986, Virtue et al 1993a. Krill accumulate lipids mainly as triacylglycerols during the spring and summer when phytoplankton are abundant (Clarke 1984, Hagen et al 1996.…”