The growth and development of macroalgae reflect the ecological status of coastal waters and create small-scale biotopes. Ten per cent of the macroalgae are washed ashore and accumulate in the surf zone in front of beaches. As far as beach tourism is concerned, algae accumulations are a major disturbing factor and require expensive beach cleaning. Climate change and the implementation of EU policy will have an impact on macroalgae growth and the associated biomass accumulations. For the development of effective adaptation measures, knowledge on the future macroalgae growth is of rising importance in tourism resorts. We use the 3D flow and ecosystem model ERGOM to simulate changes in the Baltic Sea ecosystem until 2070, resulting from climate change and the implementation of the Baltic Sea Action Plan (BSAP). Together with a geo-data analysis, these methods allow us to assess the consequences for macroalgae and its accumulation at beaches. Most important parameters for macroalgae are water transparency and the availability of hard bottom substrate. Model results show that climate change will only slightly increase the availability of hard substrate.
The BSAP has an objective to reach a good status of the Baltic Sea ecosystem by reducing the riverine nutrient loads during the next few decades. According to our model, its full implementation will reduce primary production in the Baltic Sea and increase water transparency, indicated by Secchi-depth, from six metres to about eight metres. Better light conditions and the availability of hard substrate will allow macroalgae to grow in deeper water and to cover larger areas. According to model results, an implementation of the BSAP will cause a doubling of perennial macroalgae accumulation on German Baltic beaches.