Forecasting changes in biodiversity and species distribution of phytobenthos associated with climate change.

Climate change affects species relationships and functioning of the aquatic ecosystem. Most vulnerable are species that already live near to their physiological tolerance limits. Our study included marine phytobenthos species with different environmental preferences. The potential response of species richness and distribution of selected species to climate change in the brackish environment of the Baltic Sea was investigated using the boosted regression trees modelling method. Predictive modelling of biodiversity patterns and species distributions gives a valuable insight into potential future changes which allows the application of the best monitoring and management strategies with the aim to maintain ecosystem integrity. Future species richness was predicted to decrease significantly compared to nowadays conditions. The largest biodiversity decline was predicted in areas where the present biodiversity was the highest. Biodiversity is expected to decline also spatially as highly diverse area becoming narrower along coastline. The studied species could be divided into three groups based on the predicted effect of climate change: (1) species with significant decline (Furcellaria lumbricalis, Zostera marina, Tolypella nidifica), (2) species with slight decline (Fucus vesiculosus), and (3) species that benefit from change (Chara aspera, Myriophyllum spicatum). The most significant predicted change was the decline or disappearance of brackish and marine species and the increase of freshwater species due to the expected decrease of salinity in the Baltic Sea by the end of 21^st century.