Lipid and lipid class content of the pelagic tunicate Oikopleura vanhoeffeni

Abstract

Lipid biochemistry of pelagic tunicates is poorly known, despite the fact that the larvae of several flatfish species depend exclusively on oikopleurid appendicularians at time of first feeding. Microgravimetric analysis and thin- layer chromatography with flame ionization detection (TLC- FID) were used to determine the total lipid content and lipid class composition of the pelagic tunicate Oikopleura vanhoef- feni. Our goal was to determine the dominant storage form of lipid in 0. vanhoeffeni before and after the spring diatom bloom. Lipid levels and lipid class composition were measured for all 5 ontogenetic stages of 0, vanhoeffeni, plus eggs. Levels ranged from 23 to 525 ~g ind.-' over the entire life cycle, increasing exponentially with increasing body size and ontogenetic (i.e, maturity) stage. Regression analyses showed that 84 % of the variation in the logarithm of total lipid content was explained by the logarithm of ontogenetic stage. Per unit dry weight, the mean (f SE) lipid concentration was 5 f 0.3 % before the bloom and 7.5 f 1.2 % after the bloom. Lipid class composition provided scant evidence for energy storage by 0. vanhoeffeni, with no wax esters before or after the spring bloom and moderate levels of triacylglycerols present in pre- bloom animals only. Individuals collected after the spring bloom were significantly smaller than those from before the bloom, suggesting that a spawning event had occurred some- time during the bloom. Predominant lipid classes before and after the bloom were phospholipids (65 to 90 % of total lipid) and acetone-mobile polar lipids (4 to 24 '10). Thus, although this appendicularian is a suspension feeder inhabiting very cold water, it does not store wax esters as do high-latitude copepods. Rather, 0. vanhoeffeni has the lipid characteristics of a gelatinous, opportunistic colonist, i.e. that of an omnivore with the ability to direct ingested food energy into rapid somatic growth or gamete production.