Latitudinal comparisons of physiology and feeding ecology of two warm water copepod species, Euchaeta and Pleuromamma spp. in the Northwest Pacific Ocean using lipid biomarkers

Abstract

In order to understand the latitudinal variation of physiology and feeding ecology of copepods, we examined lipid contents and compositions in warm water copepod species (Euchaeta and Pleuromamma spp.) collected from the three different regions from low (sub-tropical) to mid (temperate) latitudes in the Northwest Pacific Ocean. Total lipid contents of Pleuromamma spp. were about 5 % of dry wt. without any latitudinal differences, whereas Euchaeta spp. showed slightly higher lipid content (≈6-7% of dry wt.) 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 (accounting for more than 35% of total lipids) in Euchaeta spp., whereas, in Pleuromamma spp., phospholipids, known as the membrane components, were the dominant lipid classes (accounting for 43% of total lipids) with a trace amount of the storage lipids as a form of triacylglycerols (≤ 1 % of total lipids).Among fatty acids, polyunsaturated fatty acids (PUFA), specially Docosahexaenoic acid (DHA : 22:6(n-3)) (about 35% of total fatty acids), were most abundant in Euchaeta spp., while saturated fatty acids (SAFA), specially hexadecanoic acid (16:0) (about 30% of total fatty acids), were most abundant in Pleuromamma spp.. Among the neutral fraction of lipids, phytol, originated from the side chain of chlorophyll, was found in all samples which could indicate the feeding activity on phytoplankton. While only trace amounts of short-chain fatty alcohols were found in Pleuromamma spp., significant amounts of fatty alcohols were found in Euchaeta spp.. Particularly, 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. from low latitudes. The latitudinal variation of trophic lipid markers in these copepods could be significantly related with in-situ food ava