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The aim of this study was to analyze male and female gonad fatty acids of two sea urchin species, Paracentrotus lividus and Arbacia lixula, from the south coast of Spain. Additionally, we investigated possible diVerences between two locations. The ovaries of both species showed higher percentages of 14:0, 16:0, 16:1n-7, 18:2n-6, 18:3n-3 and 18:4n-3 than testes and lower levels of 18:0, 22:1n-9, 20:4n-6 and 22:5n-3. In P. lividus but not in A. lixula, the level of 20:5n-3 was higher in testes than in ovaries. These diVerences between sexes probably indicate diVerent requirements of males and females during gametogenesis although the presence of a large number of gametes in the mature gonad may also have inXuences on fatty acid composition. SigniWcant diVerences in gonad fatty acid proWles where also found when individuals of P. lividus collected at a location of the Mediterranean region were compared with specimens collected at the Atlantic coast. The most remarkable changes were the lower levels of 14:0, 18:1n-7, 20:1n-9, 20:4n-6 and 22:4n-6 and the higher values of 20:1n-11, 20:5n-3 and 22:6n-3 found in males and females of the Mediterranean specimens compared to those of the Atlantic coast. These diVerences probably reXect the diVerences in potential food sources at each location.

SUMMARY: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.