Distribution and importance of wax esters in marine copepods and other zooplankton

Abstract

Zooplankton were captured for detailed lipid analyses from known depth intervals in opening-closing nets and in midwater trawls to 2500m at a station in the subtropical Pacific. Copepods were also collected from the upper 500 m of a second subtropical and a temperate station in the Pacific, and a station in the Arctic. At the subtropical station wax esters were a minor part of the total lipid (less than 10%) and triglycerides were the most important lipid of many copepods inhabiting the upper 325 m, whereas wax esters were the main lipid constituent (over 50% of the lipid) and triglycerides were a minor lipid component for all copepods examined from depths below 625 m. The 325–625 m depth interval appeared to be a transition zone. Wax esters also comprised over 40% of the lipid in most of the temperate and polar calanoids examined. Triglycerides tended to be replaced by wax esters as the main lipid component in copepods from deep water or cold water. All genera examined belonging to the families Calanidae, Euchaetidae, Lucicutiidae, Heterorhabdidae, and Augaptilidae had greater than 20% of their lipid as wax esters. The genera examined from these families generally occur in deep water or near-surface cold waters. Members of the families Candaciidae and Pontellidae contained less than 10% wax ester. They are primarily found at shallow depths from tropical to temperate waters. The families Eucalanidae, Aetideidae, Scolecithtricidae, and Metridiidae contained genera with varying amounts of wax esters. These families have both genera and species which inhabit various depth and temperature ranges. Experiments on the rate of lipid utilization for periods up to one week generally showed a slow decrease in the percentage lipid of the dry weight. Detailed lipid analysis of Gaussia princeps during starvation showed triglyceride was utilized while wax esters remained relatively unchanged. The depth and latitudinal distribution of lipid in marine copepods may generally be explained on the basis of temperature or the temporal distribution, relative abundance, and rate of supply of food. However, there some exceptions, and the importance of taxonomic affinity cannot be ignored.