Abstract
Macroscopic fibrous mats formed by diatoms have been found extensively in the upper reaches of the Chikugo River, Kyushu, Japan. They are mainly aggregations of Cymbella janischii, which colonizes surfaces using mucilage stalks (secreted by the cells) that branch into tree-like shapes. In addition, Gomphoneis minuta attaches to these colonies using its own mucilage stalk. These species have not been recorded in Japan, and were probably introduced from North America. Careful monitoring of the bloom and distribution of these alien species is necessary to avoid becoming “nuisance” diatoms such as Didymosphenia geminata, which is expanding its habitat in North America, Europe and New Zealand.
