Cotonnec, G., L. Seuront, G. Thoumelin & L. Fraga-Lago. (2003). Fatty acid composition of Acartia clausi, Pseudocalanus elongatus and Temora longicornis associated with their diet in the eastern English Channel during a spring bloom of Phaeocystis sp. Mer, Tokyo. 41(1): 37-51.

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Cotonnec, G., L. Seuront, G. Thoumelin & L. Fraga-Lago

2003

41(1): 37-51.

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On the basis of two three hours resolution Lagrangian surveys conducted during three days at the beginning and the end of the 1998 spring bloom in the Eastern English Channel, we investigated the fatty acid composition of both particulate organic matter (POM) and dominant calanoid copepods (Acartia clausi, Temora longicornis, Pseudocalanus elongatus). Phytoplankton biomass was higher during the first than the second survey, and Phaeocystis sp. was the predominating algal genus (ca. 90% of total diversity), with diatoms in lower proportions. Cryptophytes and dinoflagellates were always in low levels (< 1%). Three fatty acids (14:0, 16:0, 18:0) were predominant in POM, and accounted for 75% to 96% of the total fatty acids. Unsaturated fatty acids were mainly composed by essential fatty acids (ω3 and ω6 fatty acids). Our major finding here was the highest proportions of unsaturated fatty acid, especially 20:5ω3 (EPA) and of 22:6ω3 (DHA), in copepods relatively to POM. More specifically, T. longicornis and A. clausi lipid compositions were similar, with high 20:5ω3 and 22:6ω3 contents when compared to P. elongatus which was characterised by a higher proportion of 18:1 ω9. This suggests omnivorous and carnivorous diets for the former ones and the latter, respectively. The observed shifts in POM fatty acid composition led to a decrease in the total fatty acid contents, but no change in the fatty acid composition has been observed for the three investigated species. T. longicornis was nevertheless more sensitive to changes of the dietary fatty acid composition than the two other species. Finally, we stress that the species-specific evolution of the EPA to DHA ratio indicates that the fatty acids mobilization occurred differently in each species.

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