Feasibility study for kelp afforestation in the German Bight: Habitat availability and light requirements of Laminaria hyperborea

Besides the much-needed reduction of CO₂ emissions, exploring and implementing carbon removal strategies is essential to reduce the impact of man-made climate change effects. The sequestration of CO₂ by coastal vegetated ecosystems (CVEs) presents a natural and nature-based solution. One of these CVEs is kelp forests, which are amongst the most productive and diverse marine ecosystems. Although their CO₂ sequestration potential is still being discussed, kelp forests have been increasingly mentioned within the blue carbon framework in recent years. As kelp forests worldwide are in decline, it is not sufficient to conserve these habitats, but expanding the existing and even establishing new sites is essential. As a baseline study for potential kelp forest expansion around the island of Heligoland and even afforestation measures in the German Bight, we investigated the light requirements of the brown alga Laminaria hyperborea and the in situ light climate. Our results point to a compensation irradiance of 30 μmol m⁻² s⁻¹ and a local depth limit of 12.8 m for L. hyperborea under summer conditions. Consequently, we calculated the total area with suitable light conditions for kelp growth around Heligoland to be about 24.1 km². Combining the kelps minimum light requirement, underwater light attenuation, and bathymetric maps, provides an understanding of habitat requirements based on the physiological needs of L. hyperborea and helps to identify suitable afforestation sites within the German Bight.