Thesis supervisor: Senior Research Fellow Ülo Suursaar (UT) and Senior Research Fellow Kaire Torn UT)
Opponent: Professor Mariusz Pełechaty (Adam Mickiewicz University, Poland)
Having a worldwide distribution in fresh and brackish waters, charophytes are among the most evolved algae. In the water ecosystems, they act as food, habitat and shelter resource and also provide an assessment of the status of the coastal waters. Studies of the species distribution give valuable input on biodiversity assessment. Coastal waters are relatively well studied. Unfortunately, the last investigation dedicated to charophyte species richness in the Estonian inland waters was held 60 years ago. Therefore, the goal of the given thesis is to fill the urgent need to renew information on charophyte biodiversity and give an overview of the present distribution of charophyte species in both Estonian coastal and inland waters based on the most recent data. Analysis of the occurrence patterns of charophytes in relation to environmental preferences was expected to reveal the most important factors influencing the distribution patterns of charophytes. While previous studies reported 16 charophytes species, the present study revealed 22 species of charophytes present in the Estonian waters. Most freshwater species were widespread throughout the country and their distribution reflected the corresponding distribution pattern of the inland water bodies. Brackish-water species were mostly restricted to the shallow, sheltered, soft-bottom archipelago environments, found especially in western Estonia. The factors that turned out to be the most important and that generally define geographical patterns of charophyte communities in the Estonian coastal area are depth, substrate properties and exposure to wave. The sampling-point method leaves out unstudied areas between the sampling localities and where observations have not been carried out. The predictive modeling was used to get a general assessment of the distribution of charophyte species in the coastal area, estimating probable occurrences in relation to the environmental data. Areas, where charophytes are likely to be present might be predicted by depth in the area, wave exposure and proportion of the soft sediment.