2014 Volume 76 Issue 2 Pages 99-109
In Lake Suwa, various eutrophication control measures have been taken to reduce external loads of phosphorus and nitrogen. As a result, the composition of the phytoplankton in the lake has also changed. Since 1999, blue-green algae have decreased, and Mougeotia have appeared August–December in 2011.
DNA analysis of the 18S rRNA region of Mougeotia revealed that Mougeotia in Lake Suwa come from two phylogenetic clades. A genetic distance （p-distance） of 4% indicated they are strongly differentiated and should be recognized as different species. This work has shown that there are two phylogenetic clades of Mougeotia in Lake Suwa, both of which are different from M. scalaris clades, and that many strains isolated from Lake Suwa and Lake Biwa are the same phylogenetic clades.
The longer cell length of Mougeotia in January 2012 than in November 2011 and the form of zygospores in January 2012 suggest it should be classified as M. elegantula.
Mougeotia generally occurs in oligotrophic to mesotrophic lakes, and was first found in Lake Suwa in the 1960s. The reappearance of Mougeotia in Lake Suwa in 2011 suggests that, as a result of water quality improvement, the lake is transitioning from a blue-green algae dominated eutrophic lake to a mesotrophic lake.
