Limnocalanus macrurus in the Kara Sea (Arctic Ocean): an opportunistic copepod as evident from distribution and lipid patterns

Abstract

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.

Fatty acid composition and lipid content in the copepod Limnocalanus macrurus during summer in the southern Bothnian Sea

“…Similar to our study, Hiltunen et al [21] reported high proportions of these fatty acids, especially EPA and DHA. Conversely, in the arctic Laptev and Kara Seas, much lower proportions of PUFAs have been reported [22,23] and were probably caused by high reliance on diatoms [21].…”

“…In L. macrurus, oil sac length has been used for the determination of the lipid content by Vanderploeg et al [8] in Lake Michigan, and by Dahlgren et al [6] in the Bothnian Bay. The quality of lipids in L. macrurus is poorly known, as the studies are few and they have mainly focused on populations that live in lakes [21] or in Arctic coastal waters [22,23]. In the Baltic Sea, the only study investigating the fatty acids of L. macrurus gives no information about their seasonal variation but indicates some differences from the lake populations of the same latitude [21].…”

Bioconversion of fatty acids at the basis of marine food webs: insights from a compound-specific stable isotope analysis

“…In the field, copepods likely had access to a variety of food items, since the presence of 18:0 and FA of the ω6 series point to grazing on protists or smaller animals, while odd-chain length and branched FA are good indicators of feeding on bacteria, and 16:1ω7 and EPA may result from feeding on diatoms (Kaneda 1991, Ederington et al 1995, Des vilettes et al. 1997b, Hirche et al 2003, Caramujo et al 2008.…”

“…We analysed the total FA that includes membrane FA, and although the latter are probably under metabolic control and thus weakly influenced by dietary FA (Desvilettes et al 1997b), yet it was possible to detect FA differences in total FA extracts that could be related to diet FA composition. In the field, copepods likely had access to a variety of food items, since the presence of 18:0 and FA of the ω6 series point to grazing on protists or smaller animals, while odd-chain length and branched FA are good indicators of feeding on bacteria, and 16:1ω7 and EPA may result from feeding on diatoms (Kaneda 1991, Ederington et al 1995, Des vilettes et al 1997b, Hirche et al 2003, Caramujo et al 2008.…”

“…In the field, copepods likely had access to a variety of food items, since the presence of 18:0 and FA of the ω6 series point to grazing on protists or smaller animals, while odd-chain length and branched FA are good indicators of feeding on bacteria, and 16:1ω7 and EPA may result from feeding on diatoms (Kaneda 1991, Ederington et al 1995, Des vilettes et al. 1997b, Hirche et al 2003, Caramujo et al 2008.Based on the feeding experiments, the maintenance of the FA weight content of copepods and high survival rate indicates that Navicula phyllepta is a suitable diet for copepod nutrition. The assimilation of diatom FA in terms of carbon largely mirrored the abundance of FA available in the diet, which resulted in a higher amount of C16 FA, EPA and DHA in the copepod after 9 d of feeding on the diatoms relative to the copepod composition at the start of the experiment.…”