Discovery of living populations of a purported fossil diatom: Aulacoseira scalaris from two lakes in the Vosges Mountains (France)

As a part of the Monitoring Program of the European Water Framework Directive, the phytoplankton of water bodies over 50 hectares have been studied in the Rhine-Meuse river basin. During the analysis, the centric diatom Aulacoseira scalaris (Grunow in Van Heurck) Houk, Klee & Passauer was identified from Longemer Lake in 2010 (Xonrupt- Longemer, France) and Gérardmer Lake in 2011 (Gérardmer, France). The presence of this diatom was again confirmed in samples collected in 2014 from both lakes. Interestingly, Aulacoseira scalaris until recently has been found only in fossil to subfossil materials from U.S.A. (State of Oregon and Virginia City, State of Nevada) and France (Vosges Mountains, Gérardmer Lake). The species has been observed for the first time in live material and should no longer be considered as strictly fossil or subfossil. Information on its autecology is provided using the physicochemical data of the lakes, and its morphology is compared with similar species of Aulacoseira in available literature.