The lake La Godivelle-d'en-Haut (French Massif Central) is a mountain lake which is characterized by low temperatures and a very low primary production. In this ecosystem with restricting abiotic and biotic conditions, the zooplanktonic community is largely dominated by the calanoid copepod Mixodiaptomus laciniatus who, with his large lipid reserves, is active all around the year. Therefore, our study search to know how these lipid reserves (wax esters and triacylglycerols) are accumulated and used by the different developmental stages of the copepod. The trophic relationships between this small crustacean and the microbial communities were studied by concomitant use of pigment, fatty acid and sterol biomarkers. Our results obtained in the laboratory and in situ show that the copepod preferentially feed on cryptophyceae, bacillariophyceae and chlorophyceae. Nevertheless, high proportions of C15 + C17 fatty acids in the calanoid suggest that HNF and/or heterotrophic bacteria also contribute to his food. However, CV-Ad. stages accumulate the most important lipid reserves in autumn, during the high development of the chlorophyceae Sphaerocystis. These reserves sustain the next reproduction and are allocated to eggs to allow development of the first naupliar stages in spring. Thus, our study show the importance of the autumnal phytoplanktonic bloom and tend to suggest that Mixodiaptomus, by its life cycle, has developed a set of ecological, physiological and biochemical strategies to allow his durability in this ecosystem.
