The Baltic Sea is a young brackish marginal sea characterized by a pronounced salinity gradient from south-west to north-east and clear seasonal changes in temperature and nutrient availability. Therefore, the Baltic Sea allows the cultivation of a limited number of macroalgae species. In addition, the Baltic Sea is under high anthropogenic pressure due to human activities both on land and at sea, including maritime industries, coastal urbanization and tourism, and fertilizer inputs by agriculture and forestry. There is an utmost need to restore the degraded ecosystems of the Baltic Sea and here, macroalgal cultivation is a promising circular economy solution to locally achieve nutrient reduction (Kotta et al., 2022). However, for this potential to be unlocked, the safety of upscaling has to be assured. Therefore, macroalgal cultivation must follow clear monitoring and control frameworks to avoid unnecessary damage to the fragile and valuable habitats of the Baltic Sea. Indeed, lessons learned in other parts of the world provide the possibility to choose low-risk solutions for seaweed aquaculture in the Baltic (Campbell et al., 2019, Tonk et al., 2021, Banach et al., 2022).
The goal of this report is to review the current knowledge and identify the necessary procedures and monitoring practices when starting or expanding a seaweed farm in the Baltic Sea. The suggestions are provided considering the variability of the Baltic Sea environment. Seaweed cultivation is known to improve ecosystem functionality and safeguard several ecosystem services (e.g. Kotta et al., 2022). In the text, we distinguish cultivation from wild harvesting practices. Collecting beach wrack is out of the scope of this report, as it is regulated by terrestrial procedures of biowaste management.