Elemental composition, metabolic activity and growih of Antarctic krill Euphausia superba during winter

Abstract

Euphausia superba Dana was collected at stations encompassing 3" of latitude in icecovered waters west of the Antarctic Peninsula in winter of 1992 (July-August), and in the same region the previous summer (December-January). There was no significant change in any biometric index (dry weight vs length, carbon vs dry weight, nitrogen vs dry weight, or body C:N). Rates of ammonium excretion in winter were not significantly different from those previously reported for E. superba in summer. It was clear that E. superba fed as a carnivore in winter. Copepod body parts consistently occurred in M 1 guts. During winter shipboard experiments, freshly caught krill ingested copepods and produced faeces at rates comparable to those measured in summer. The low ratio of N:P excretion (2.02) also suggests carnivorous feeding. A physiological model of carbon and nitrogen metabolism indicates that E. superba must feed during winter to maintain its observed C : N ratio and rate of ammonium excretion. On a diet of less than 1 Metridia gerlachei female copepod per day, a 20 mm knll can grow with a growth efficiency comparable to that achieved in summer. We suggest that starvation, body shrinkage and reduced metabohsm are unusual behaviors for knll in winter, and that carnivory sustains growth until ice algae become available as food in late winter and early spring.

The overwintering of Antarctic krill, Euphausia superba, from an ecophysiological perspective

“…In contrast to other overwintering studies, Huntley et al (1994) reported high feeding activity of krill on small zooplankton organisms such as Oithona and Oncea and Marschall (1988) on sea ice algae in winter. Actually, the latter study took place at the onset of spring and not as the title states in winter (Hempel 1987).…”

“…The seasonal change in light intensity in the Southern Ocean might also be responsible for seasonal variability in metabolic activity (Kawaguchi et al 1986;Torres et al 1994b). Huntley et al (1994) even showed high metabolic rates and feeding activity on zooplankton of krill during winter and suggested that krill did not adopt speciWc mechanisms for overwintering. Until end of the 1990s, although most studies on krill larvae during winter had mainly focused on their distribution and abundance (e.g.…”

“…• Zooplankton (Huntley et al 1994) • Seabed detritus (Kawaguchi et al 1986) • Ice algae (e.g. Hamner et al 1983;Marschall 1988;Spiridonov 1992) The relative importance of the proposed overwintering mechanisms was diYcult to judge because they have been observed separately or together at diVerent times and places.…”

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

“…Within the polar lipid group, the cluster analysis also separated those organs and stages with high PC, low triglycerides and PE content lower than 4.5 % (gonad and digestive gland from mature females and fat body from subadults) from those with lower PC, low triglycerides and PE content higher than 4.4% (abdomen from males, mature and post spawn females, and subadults; stomach from mature females and subadults). The relation between wet weight and body length for the population sampled during FIBEX did not differ significantly from relations reported elsewere (Kato et al 1982, Morris et al 1988, Farber-Lorda 1994, Huntley et al 1994. No significant differences were found between maturity stages, and a mean value of the allometric exponent b of 3.12 was computed, suggesting isometric growth (i.e.…”

A laboratory study on digestive processes in the Antarctic krill, Euphausia superba , with special regard to chitinolytic enzymes

“…As ®lter feeders, krill feed mainly on phytoplankton. Primary production in Antarctic waters is, however, characterized by high seasonal and spatial variation (El-Sayed and Taguchi 1981;ElSayed and Weber 1982) and, potentially, E. superba can also change to carnivorous feeding at low phytoplankton densities or during the Antarctic winter (Price et al 1988;Lancraft et al 1991;Huntley et al 1994;Atkinson and SnyÈ der 1997;Pakhomov et al 1997). Krill are able to graze on patchy food sources very e ciently (Hamner et al 1983).…”