Fatty acid composition of the Caprellidea (Crustacea: Amphipoda) from the Strait of Gibraltar

Abstract

The total fatty acid composition of nine species of caprellidean amphipods collected from the Strait of Gibraltar was investigated. All caprellids were characterised by high levels of polyunsaturated fatty acids, mainly eicosapentaenoic acid, 20:5(n-3), and docosahexaenoic acid, 22:6(n-3); other major fatty acids were the saturate palmitic acid, 16:0, and the monounsaturate oleic acid, 18:1(n-9). In spite of this general uniformity, univariate and multivariate analysis showed that Caprella acanthifera and C. grandimana differed from the remaining species (C. danilevskii, C. equilibra, C. liparotensis, C. penantis, C. santosrosai, Phtisica marina and Pseudoprotella phasma). These two species (C. acanthifera and C. grandimana) showed higher concentrations of 18:1(n-7) and 20:4(n-6) and lower percentages of 22:6(n-3). These results, together with higher values of the biomarker ratio 20:5(n-3)/22:6(n-3) and a lower ratio 18:1(n-9)/18:1(n-7), suggested a greater contribution of diatoms and macroalgae in the diet of C. acanthifera and C. grandimana and a lesser contribution of flagellates than in the remaining species. The cluster classification of the caprellid specimens from the Strait of Gibraltar based on the fatty acid composition was in agreement with the Cluster output from data of feeding behaviour. Sex-related changes in the fatty acid composition were also explored in C. acanthifera, C. danilevskii and C. penantis; the percentage of 18:0, 20:4(n-6), and 20:5(n-3) was significantly higher in males, whereas 16:1(n-7) was higher in females. The intraspecific differences of fatty acids in different environmental conditions seem to indicate that the consumption of diatoms in contrast to flagellates increases with the degree of eutrophication.