Abstract
Two large-celled bacterial species, Chromatium sp. and Macromonas sp., densely populate the mid-depth of Lake Kaiike, a small lagoon on Kamikoshiki Island, turning the water a purplish red (bacterial plate). In recent years, the Chromatium population has showed large seasonal fluctuations; maximum cell numbers in the order of 106 cells ml-1 have dropped to 103 cells ml-1. To examine the factor(s) disturbing the population, the profiles of two bacterial species as well as environmental factors were examined during the period June 1998 to Oct. 2001. Solar heating to raising the water temperature above 30°C as well as a proliferation of Macromonas sp. were found to have disturbed the Chromatium population.
