Studies on feshwater lakes & rivers

I am studying microbial organisms and communities that live in freshwater lakes, ponds, and rivers. My major is the ecology of photosynthetic microorganisms, and I have mainly studied phytoplankton in lakes and ponds and attached algae in rivers. When I was a graduate student, an increase in ultraviolet radiation (UVB) reaching the earth surface due to ozone depletion in the ozone layer caused concern, and many studies were conducted to clarify the effects of solar UV radiation on terrestrial and aquatic organisms. Using periphyton communities in river systems, I studied the effects of UVB radiation on attached algae and bacteria and clarified the difference in sensitivity among the organisms and the interaction between attached bacteria and algae during the development of periphyton community.


Recently, I have been studying the cyanobacteria which form freshwater blooms in lakes and ponds. I'm also interested in the ecology of Cryptomonas (Cryptophyta) species composition in freshwater systems. Genus Cryptomonas distributes from oligo- to eutrophic lakes and ponds and has different morphologies. Many researchers have studied the genus taxonomically since mid 19 century. On the other hand, recent studies using DNA sequence analysis indicate that Cryptomonas includes heterotrophic species. Moreover, some species show dimorphisms, for example, the algae previously identified as genus Campiromonas are one ecotype of certain Cryptomonas species. Therefore, the taxonomy of Cryptomonas has been reconstructed based on 18S rDNA sequence etc. In Japan, taxonomical studies of Cryptomonas species have been studied but I believe reclassification of the Cryptomonas species distributed in Japan will be necessary. As a preliminary study, we studied seasonal variation in Cryptomonas species composition in Lake Hira, Japan, using the Single-cell PCR method. We found two spices which had not been reported in Japan and two new lineages. As these species were detected in only one lake, I think it is necessary to study Cryptomonas species in many more lakes and ponds.


As mentioned above, I am studying algae mainly. However, I am collaborating with students and other researchers who are studying other microorganisms in freshwater systems. Microorganisms consist of various organisms. Thus we need to clarify interactions between the various microorganisms to understand the ecosystem and food web in aquatic systems. Collaboration with students and other researchers is thus very important.