Diversity and conservation of desmids in Bornholm, Denmark – revisiting after 130 years
20 August 2018
Hansen, Gert; Stastny, Jan; Moestrup, Ojvind; Lundholm, NinaDesmids are unicellular green algae dominating habitats that are vulnerable and highly threatened, like raised bogs, mires and fens. Desmid diversity was studied in four different localities on the Danish island Bornholm. A total of 186 species, 58 of which not recorded from Denmark before, were observed. Species composition from the locality ‘Kohullet’ was compared to more than 130 year-old records. In 1880s this locality contained 59 species vs. 70 in in the present study. The species composition has changed towards more oligo-mesotrophic and more acidophilic species. The reasons for these changes may be due the 1960-70s increase in atmospheric deposition of nitrous- and sulphurous oxides leading to a pH-decrease, and the possible use of Kohullet in the 1880s for cattle drinking leading to more mesotrophic conditions than present days conditions. We used an empirical system developed by Coesel for classifying the trophic state or ‘conservation value’ of freshwater habitats using desmids as indicator organisms. All localities studied had maximum scores, i.e. represented highly structured and well-balanced ecosystems. Thirty of the recorded species were potential Red List species, using the Dutch Red List criteria for desmids. We suggest that Kohullet should be considered an Important Plant Area (IPA), as it has a high diversity of desmids, a long history of algal records including desmids and may be considered a threatened habitat of major significance to desmids. Furthermore, it is suggested that several desmids are considered Red List species.