Predicting the Impact of Climate Change on the Distribution of the Key Habitat-Forming Species in the Ne Baltic Sea

Macrophytes provide food, shelter and habitat for a multitude of other species and are therefore considered as important habitat-forming species. Loss or decrease of habitat-forming species severely affects biodiversity and functioning of coastal marine ecosystems. In the brackish Baltic Sea, such special, structuring species are large perennial macroalgae Fucus vesiculosus and Furcellaria lumbricalis on hard seabed and eelgrass Zostera marina and charophytes (Chara spp.) on soft substrates. The Baltic Sea is expected to face severe changes in environmental conditions due to climate change by the end of the 21st century, e.g. decrease in salinity and increase in temperature, wind speed, and storminess. It is essential to forecast changes in the distribution of valuable species in order to provide data for marine environmental protection and management decisions. Boosted regression trees modelling method was used to produce current species distribution models and predict the potential changes based on future climate scenario. Data from over 10 000 benthic sampling sites were used as an input for distribution models. Following the influence of the water depth, the next major drivers of species distribution were substrate type for Fucus, temperature for the charophytes and Furcellaria, and salinity for Zostera. Based on the model predictions, the climate change may cause a significant reduction of the distributional range of Zostera and Furcellaria. Slight decline of Fucus was also detected. Unlike the other habitat-forming species, charophytes are potential winners by probably increasing their distribution in the future. However, charophytes are not able to replace the niche of the other key habitat-forming species due to different substrate, wave exposure and salinity preferences.