Offshore solar farms as habitats for Mytilus edulis: A preliminary modelling study on mussel growth, distribution, chlorophyll-a uptake and bio-deposition in the North Sea.

Emerging offshore solar technology offers a promising solution for global energy demands while addressing land scarcity. As the sector expands, understanding its environmental impact is crucial. The blue mussel (Mytilus edulis) has been observed inhabiting these new substrates. This first-of-its-kind study addresses the environmental interactions between offshore solar farms and mussel growth across solar farms of up to 1 km in size, in the Dutch North Sea. A marine growth model, based on Dynamic Energy Budget (DEB) theory and coupled with 1D hydrodynamic forcings predicts the spatial distribution, size and mussel biomass, chlorophyll-a uptake and bio-deposition. Results show spatial differences in mussel growth linked to varying chlorophyll-a availability at different farm locations as a result of current circulation. At smaller farms, individual mussels grow to larger sizes and accumulate more energy reserves, whereas at larger farms, individual growth is constrained. In fact, larger solar farms exhibit relatively less individual mussel biomass due to reduced chlorophyll-a availability beneath the floating structures. Mussel growth is associated with localized changes in chlorophyll-a levels, though these effects are spatially limited. Organic matter deposition also mirrors these spatial variations. Given the vastness of the sea relative to the expected horizontal footprint of offshore solar installations, the environmental effect of mussel-related chlorophyll-a uptake and bio-deposition is foreseen to be spatially limited. These findings provide a foundation for further environmental assessments of offshore solar installations. Achieving sustainable energy production at sea requires integrating advanced technology while understanding, and mitigating potential environmental impacts.