The chemical composition of seaweed is largely controlled by environmental conditions (light, temperature, salinity and wave-action) and nutrient availability. This presents opportunity for their controlled physiological manipulation by adjusting growth conditions according to the desired seaweed composition: the specific conditions required will depend on seaweed species of interest. This second SeaChem breakthrough innovation will be investigated in WP2. First, the optimum growth conditions will be identified in lab-scale tests for selected seaweed species with an existing market to achieve desirable biomass composition for bulk products, with additional optimization of species-specific high-value novel by-products including fatty acids, carotenoids, mycosporine-like amino acids and phycobiliproteins (DC5). Furthermore, explicit areas at sea will be explored (geographic location) that should provide the required environmental conditions and availability of elements for specific species of seaweed to generate the desired chemical composition for further valorization. Polysaccharides (including alginates, agars or carrageenans) are currently the primary components of commercial interest that are sourced from seaweed. Most of the industrially relevant polysaccharides are structural polysaccharides, part of the cell wall, or storage polysaccharides. However, during the cultivation of seaweed, other polysaccharides are also excreted as part of their defense strategies. This offers a secondary source of polysaccharides that will be optimized through manipulating growth parameters such as light, temperature, nutrients, CO₂ and other parameters such as wave-action (DC6).