Latitudinal variation of lipid contents and compositions in copepods, Euchaeta and Pleuromamma spp., from the Northwest Pacific Ocean: Its implication in feeding ecology

Abstract

In order to understand the latitudinal variation of lipid contents and compositions in copepods, we collected two copepod species, Euchaeta and Pleuromamma spp., from low to mid latitudes in the Northwest Pacific Ocean. Total lipid contents of Pleuromamma spp. were about 10 μg•ind–1 with little latitudinal variation, whereas Euchaeta spp. showed slightly higher lipid content (≈ 17μg•ind–1) than Pleuromamma spp. with the latitudinal gradient (low at sub-tropic and high at temperate). Wax esters, known as the major storage lipid classes, were found to be the dominant lipid classes (≥35% of total lipids) in Euchaeta spp., whereas in Pleuromamma spp., phospholipids, known as the membrane components, were the dominant lipid classes, with an exception of specimens from warm pool regions, showing the dominance of storage lipids as a form of triacylglycerols. Among fatty acids, polyunsaturated fatty acids, especially docosahexaenoic acid (DHA: 22:6(n-3)), were most abundant in Euchaeta spp., while saturated fatty acids, especially hexadecanoic acid (16:0), were most abundant in Pleuromamma spp. Among the neutral fraction of lipids, phytol, originating from the side chain of chlorophyll, was found in all samples which could indicate feeding activity on phytoplankton. While only trace amounts of short-chain fatty alcohols were found in Pleuromamma spp., significant amounts of long-chain monounsaturated fatty alcohols (20:1 and 22:1), generally known to be found in cold water copepod species, were found in Euchaeta spp. The latitudinal variation of trophic lipid markers in these copepods could be significantly related with in-situ food availability and species-specific diet preference.