Ecology and distribution of protists in brackish water lakes

Abstract

A brackish water area means water that is a little salty, indicating salinity between fresh and marine waters. While it is known as the habitat for many diversifi ed organisms, it is a harsh environment due to changes in salinity. Although it has been speculated for many years that biodiversity is lowered at a salinity of 5-8 ‰ within the salinity gradient in the brackish water area, planktons such as planktonic protists, in particular, have been recently found to rather increase their diversity in this salinity range. Planktonic protists are not likely to create new species easily that inhabit only specified areas, because their small size makes it easy for them to expand their habitat areas and less likely for them to be extinguished. In reality, endemic species are found in many places including brackish water areas, but we do not have a clear explanation for this discrepancy. Lake Shinji and Lake Nakaumi are the prominent brackish water lakes in Japan. In these lakes, a halocline is formed, as in many other brackish water lakes. This chapter provides an overview of the survey of protist diversity in these lakes, with an attempt to determine the environmental factors influencing the composition of species in the brackish water area.