Effects of climate change on the occurrence of charophytes and angiosperms in a brackish environment

ABSTRACT The potential response of occurrence of charophyte and angiosperm communities to climate change in the brackish environment of the Baltic Sea was investigated using the boosted regression trees (BRT) modelling method. The aim of the study was to analyse sensitivity of various species to climate change and to predict the changes in species’ distribution under projected changes of environmental variables. The results showed that depth was the most influential environmental variable in predicting the spatial distribution of charophytes and angiosperms. Other environmental variables had notably lower importance in determining community structure and the order of importance was species specific. The exceptions were the charophytes Chara horrida and C. tomentosa, for which the influence of wave exposure was stronger than the influence of depth. The studied species could be divided into three groups based on the predicted effect of climate change: (1) species that benefit from change (Chara connivens, Potamogeton perfoliatus, Myriophyllum spicatum, C. aspera, C. baltica, C. canescens, Ruppia maritima), (2) species with no notable change (Chara tomentosa, C. horrida, Stuckenia pectinata), and (3) species that decline (Zostera marina, Zannichellia palustris, Tolypella nidifica). Currently, the shallow and sheltered West Estonian Archipelago Sea hosts favourable habitat conditions for most of the charophyte and angiosperm species. 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.