Climate change is threatening marine ecosystems by affecting the physiology of organisms along the entire marine food web. At its basal levels, the energy transfer is highly variable and depends on the link between primary producers and consumers. Primary producers synthesize polyunsaturated fatty acids (PUFAs), which are stored in high amounts by their grazers: harpacticoid copepods. These PUFAs are essential dietary constituents for higher trophic levels. However, copepods can, in contrast to fish or humans, also synthesize and upgrade these PUFAs themselves. Several aspects on the genes involved in PUFA synthesis by copepods remain insufficiently understood. This research aims to study PUFA biosynthesis in Crustacea in the context of their evolutionary history and their performance under future environmental conditions. The central hypothesis is that both evolution and environment shape the capacity of primary consumers for PUFA bioconversion. We aim to generate a transcriptome of the intertidal harpacticoid Platychelipus littoralis exposed to different diet, temperature and pH treatments. Molecular and bioinformatic tools will be used for de novo transcriptome assembly and gene expression profiling of putative PUFA metabolism genes. Results will be integrated with fatty acid profiles and validated with quantitative PCR. A comparison with the metabolic pathways of water fleas will yield new insights in the evolution of the PUFA metabolism of different crustacean orders.