Limnocalanus macrurus in the Kara Sea (Arctic Ocean): an opportunistic copepod as evident from distribution and lipid patterns
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Limnocalanus macrurus is an important member of the zooplankton communities of the Siberian shelf seas. During the cruise, Boris Petrov 1999, in August/September to the southern Kara Sea and the Ob and Yenisej estuaries, its abundance and vertical distribution were investigated. In adults, salinity tolerance, egg production, feeding and lipid composition were studied. L. macrurus occurred in water with salinities ranging from 1.7 to >33 without clear preference, as revealed from salinity-tolerance experiments. The dominance of adults and their high wax-ester content, as well as the lack of egg production and feeding activity, suggest that the population was in the pre-overwintering condition. Wax esters allow L. macrurus to survive long starvation periods and to reproduce in times of little food availability, but through its potential carnivory, it should be able to replenish its diet by preying on other zooplankton. Morphology and swimming behaviour of L. macrurus resemble the omnivorous copepod Metridia longa, which, however, is mainly found in the open ocean. The overall lipid composition and the mode of lipid storage also point to an omnivorous feeding behaviour. However, the high proportion of the marker fatty acid 16:1(n-7) suggests that L. macrurus strongly exploited the existent phytoplankton bloom, consisting mainly of diatoms. A striking characteristic of its lipids is the high level of the 20:1(n-7) fatty alcohol in addition to the 18:1(n-7) fatty acid and alcohol. It is the first copepod species known to produce such high amounts of 20:1(n-7) alcohol. Since this alcohol and the corresponding fatty acid are not abundant in any prey, this long-chain monounsaturated wax-ester moiety has to be produced de novo. Owing to these particular lipid characteristics in its distribution, feeding, and life-cycle strategy, L. macrurus can be described as a very versatile and opportunistic copepod.