Lipids of four boreal species of calanoid copepods: origin of monoene fats of marine animals at higher trophic levels in the grazing food chain in the subarctic ocean ecosystem

Abstract

Abstract The total lipids of four boreal species of calanoid copepod, Neocalanus cristatus K ROYER , Neocalanus flemingeri M ILLER , Eucalanus bungii G IESBRECHT , and Metridia okhotensis B RODSKY caught in the northwestern Pacific Ocean were analyzed. The major components in the lipid classes were wax esters (WE) and triacylglycerols (TAG), and the WE were grouped according to their polarity into two types of esters (less polar WE I and more polar WE II). TAG were the dominant acyl neutral lipid (72.7–88.2%: 83.6±6.6%) in the two stages of E. bungii , and WE (WE I as a major component, 52.5–56.2%: 54.8±1.6%; WE II as a minor component, 31.6–40.0%: 34.8±3.9%) were found to be the dominant lipids of the other three species (genera Neocalanus and Metridia ). The fatty acid and alcohol profiles of the WE I in the two species ( N. cristatus and N. flemingeri ) were very similar to each other, and these acids and alcohols mainly consisted of saturated (14:0 and 16:0) and monoenoic fats (20:1 and 22:1). Those of the WE II mainly consisted of polyunsaturated fatty acids (PUFA, 16:4 n −3, 18:3 n −3, 20:5 n −3, and 22:6 n −3) and saturated and monoenoic alcohols (16:0, 20:1, and 22:1). The majority of the fats in the lipids of Me. okhotensis , which slightly differed from other species, were short-chain fatty acids (16:1 and 18:1 in WE I) and alcohols (12:0, 14:0, and 16:0 in WE II). In the total fatty acids and alcohols of the WE, the monoene fats were the dominant components (mean calculated by the respective percentage of fatty acids and alcohols in that of total fats: 38.4±0.7% for the fatty acids; 71.3±1.8% for the fatty alcohols). Most of the TAG contained in the lipids of E. bungii had various components that were similar to those of other marine organisms, such as all of the pelagic fishes, and the mean level of total monoene fats was 35% (36.1±0.2%) of the total fatty acids. The major fatty components of the WE and TAG fats in all of the species were monoenoic fats, and their mean levels reached 51.5±0.6% of the total fatty acids and alcohols. We suggest that the lipids of these copepods may be a source of the monoene fats of other higher marine animals, such as lantern fish, herring, capelin, and saury, which actively prey on these copepods and accumulate high levels of these monoene fats.