Lipid biomarkers and trophic linkages between phytoplankton, zooplankton and anchovy (Engraulis encrasicolus) larvae in the NW Mediterranean

Abstract

Identification and quantification of the main fatty acids in phytoplankton, zooplankton and Engraulis encrasicolus larvae were used to study the relationship among the different trophic levels. Three northwestern Mediterranean sea areas were studied as representative of potentially heterogeneous environments. HPLC pigment analysis was performed to assess the contribution of different phytoplankton groups to total chlorophyll biomass. In spite of the physical variability, a homogeneous pattern in phytoplankton composition among areas was found, with the Prymnesiophyceae representing more than half of the phytoplankton chlorophyll biomass. This homogeneous spatial pattern was also reflected in the phytoplankton fatty acid proportions. Thus, significant amount of 14:0, 18:1(n-9) and 18:4(n-3) could be related to the dominance of the prymnesiophytes; the low proportion of fatty acid markers of diatoms and dinoflagellates agreed with the low abundances of those phytoplankton groups. Zooplankton fatty acids also showed homogeneous proportions in the studied areas, with a preferential accumulation of 16:1(n-7) and 20:5(n-3), and 22:6(n-3). This observation may indicate a preferential grazing on diatoms and dinoflagellates. Anchovy larvae displayed differing fatty acids contributions related to size. Large larvae contained a higher proportion of polyunsaturated fatty acid (PUFA). Small larvae showed a high percentage of 18:1(n-9) and 18:4(n-3) fatty acids, considered Prymnesiophyceae biomarkers. These results suggest an additional food resource for the anchovy that is complementary to a zooplankton diet, but probably of protozoan origin (i.e. microzooplankton). Significant logarithmic relationships were found between dry mass and 20:5(n-3) and 22:6(n-3) fatty acid proportions in E. encrasicolus larvae. These PUFA are considered essential for the fish-larvae development.