Functional biodiversity of lipids in Antarctic zooplankton: Calanoides acutus, Calanus propinquus, Thysanoessa macrura and Euphausia crystallorophias

Zooplankton samples were collected in January 1993 off Dronning Maud Land a long a transect from open waters to the marginal ice zone close to the Anta rctic ice shelf. Thysanoessa macrura was caught in open waters while Calano ides acutus and Calanus propinquus were mainly sampled between ice floes in the marginal ice zone. The "ice-krill" Euphausia crystallorophias was foun d over the shelf directly associated with ice flees. T. macrura had a lipid content up to 36% of its dry weight with the dominant lipid class, wax est er, accounting for 45-50% of the total lipid. The predominance of 18:1 fatt y alcohols is the striking characteristic of the wax esters. Small specimen s of E. crystallorophias had lipid levels up to 26% of their dry weight wit h, unexpectedly, triacylglycerols being the dominant lipid (up to 41% of to tal lipid). The small levels of wax eaters in these animals (3-6% of total lipid) had phytol as a major constituent. Large specimens of E. crystalloro phias had up to 34% of their dry weight as lipid, with wax esters (47% of t otal lipid) dominated by 16:0 and 14:0 fatty alcohols as the major lipid. C alanus propinquus had lipid levels of up to 34% of their dry weight, with t riacylglycerols (up to 63% of total lipid) being the dominant lipid. High l evels of 22:1 (n-9) fatty acid were present in the triacylglycerols. Calano ides acutus had lipid levels up to 35% of the dry weight with wax esters ac counting for up to 83% of total lipid. High levels of (n-3) polyunsaturated fatty acids were recorded with 20:5(n-3), 22:6(n-3) and 18:4(n-3) being th e dominant moieties. On the basis of their lipid compositions we deduce tha t: (1) Calanoides acutus is the strictest herbivore among the four species studied, heavily utilizing the typical spring bloom; (2) T. macrura is esse ntially omnivorous, probably utilizing the less defined bloom situations fo und in oceanic waters; (3) E. crystallorophias is an omnivore well adapted to utilize both a bloom situation and to feed on ice algae and micro-zoopla nkton associated with the ice; (4) Calanus propinquus seems to be the most opportunistic feeder of the four species studied, probably grazing heavily on phytoplankton during a bloom and, during the rest of the year, feeding o n whatever material is available, including particulates, flagellates and o ther ice-associated algae. We conclude that the different biochemical pathw ays generating large oil reserves of different compositions, enabling speci es to utilize different ecological niches, are major determinants of biodiv ersity in polar zooplankton.