Marine Biology Research Division

The lipids of water-striders from three different aquatic environments (marine-Halobates germanus and Halobates sericeus; estuarine- Rheumatobates aestuarius; and freshwater- Gerris remigis) differ considerably in their fatty acid composition. The polyunsaturated 22:6 fatty acid, present only in Halobates, is presumably derived from its marine plankton food. The 20:5 acid is a major component of the lipids of Gerris and Rheumatobates, which feed on terrestrial insects known generally to lack long-chain  (> C-18) polyunsaturated acids; it is presumably synthesized by chain elongation from C-18 precursors. Differences in food and habitat may account for some of the observed differences in fatty acid composition.

Neutral triglyceride lipids are stored in all three genera: in Halobates this fraction represents 74-92s of the total lipid, while in Rheumatobates and Gerris it is only 46-720/O.  The triglycerides are rapidly utilized during starvation by Halobates and Rheumatobates.  Pristane, the major hydrocarbon of many marine zooplankton, is apparently absent from the lipids of Halobates.