Biometry, isotopic composition and diet of Arctic charr (Salvelinus alpinus) from Lake Aigneau, Northern Quebec

Two modal size groups of sexually mature Arctic charr (Salvelinus alpinus) differing in shape and found at different depths in Lake Aigneau in the Canadian sub-Arctic are described and tested for genetic and ecological differentiation. Forms consisted of a small littoral resident, mean size 21.7 cm, and a large profundal resident, mean size 53.9 cm. Mitochondrial DNA analysis indicated that seven of eight haplotypes were diagnostic for either the littoral or profundal fish, with 66.6% of the variation being found within form groupings. Pairwise tests of microsatellite data indicated significant differences in nine of 12 loci and a significant difference between the forms across all tested loci. Molecular variation was partitioned to 84.1% within and 15.9% between forms and suggestive of either restricted interbreeding over time or different allopatric origins. Stable isotope signatures were also significantly different, with the profundal fish having higher d13C and d15N values than the littoral fish. Overlap and separation, respectively, in the range of form d13C and d15N signatures indicated that carbon was obtained from similar sources, but that forms fed at different trophic levels. Littoral fish relied on aquatic insects, predominantly chironomids. Profundal fish were largely piscivorous, including cannibalism. Predominantly empty stomachs and low per cent nitrogen muscle-tissue composition among profundal fish further indicated that the feeding activity was limited to the winter when ice-cover increases the density of available prey at depth. Results provide evidence of significant differences between the modal groups, with origins in both genetics and ecology.

Biometry, and fatty acid and fatty alcohol composition of the Arctic ctenophore Mertensia ovum from Kongsfjorden

Lipids of the Arctic ctenophore Mertensia ovum, collected from Kongsfjorden (Svalbard) in 2001, were analysed to investigate seasonal variability and fate of dietary lipids. Total lipids, lipid classes and fatty acid and alcohol compositions were determined in animals, which were selected according to age-group and season. Changes in lipids of age-group 0 animals were followed during growth from spring to autumn. Total lipids increased from May to September. Lipids as percentage of dry mass were lowest in August indicating their use for reproduction. Higher values occurred in September, which may be due to lipid storage for overwintering. Wax esters were the major lipid class accounting for about 50% of total lipids in age-group 0 animals from July and August. Phospholipids were the second largest lipid fraction with up to 46% in this age-group. The principal fatty acids of M. ovum from all age-groups were 22:6(n-3), 20:5(n-3) and 16:0. Wax ester fatty alcohols were dominated by 22:1(n-11) and 20:1(n-9) followed by moderate proportions of 16:0. The unique feature of M. ovum lipids was the high amount of free fatty alcohols originating probably from the dietary wax esters. In May, free alcohols exhibited the highest mean proportion with 14.6% in age-group 0 animals. We present the first data describing a detailed free fatty alcohol composition in zooplankton. This composition was very different from the alcohol composition of M. ovum wax esters because of the predominance of the long-chain monounsaturated 22:1 (n-11) alcohol accounting for almost 100% of total free alcohols in some samples. The detailed lipid composition clearly reflected feeding of M. ovum on the herbivorous calanoid species, Calanus glacialis and C. finmarchicus, the abundant members of the zooplankton community in Kongsfjorden. Other copepod species or prey items seem to be less important for M. ovum.