Fucus vesiculosus occurs in both sheltered and wave-exposed shores, with the morphotype var. linearis typically dominating exposed habitats. Its close relative F. spiralis often overlaps in distribution, and occasional hybridisation raises questions about introgression between the species. This project investigates how environmental conditions and genetic background shape morphological traits in F. vesiculosus, and to what extent F. spiralis alleles contribute to local populations. We combine trait measurements with genome-wide data from RAD sequencing to examine gene–environment associations and quantify introgression rates. This approach will help clarify the balance between local adaptation, plasticity, and hybridisation in shaping the ecology and evolution of Fucus.