Fatty acids as organic markers for the study of trophic relationships in littoral cladoceran communities of a pond

Abstract

The fatty acid (FA) composition of zooplankton and paniculate matter (including phytoplankton) associated with the submerged vegetation of a pond shoreline was analysed by gas chromatography. The FA of paniculate matter was characterized by fluctuating proportions of polyunsaturated FA (PUFA), comprising between 31.7 and 51.1% of total FA and originating from phytoplankton. Important levels of bacterial FA (branched 15:0 and 17:0) and detrital FA (17:0, 17:1) were also detected. Littoral zooplankton was dominated by two cladocerans: Eurycercus lametlatus and Simocephalus velulus. Their triacyglycerol fatty acids (TAG-FA) were characterized by PUFA (18:2(n-6), 18:3(n-3). 20:5(n-3)) originating in phytoplankton and periphytic algae, and also by bacterial and detrital odd-numbered FA. An unusual unsaturated FA (22:2(n-6)) was detected in the trophic web. It was incorporated into cladoceran polar lipids, together with long 22-carbon FA of (n-6) series. Unsaturation of polar lipids was inversely correlated with water temperature in both cladocerans. The influence of dietary FA on the composition of polar lipid FA is also considered.