Possibility for bio-control of harmful diatom blooms in Coscinodiscus wailesii by marine bacteria

Abstract

In recent years, increasing interest has focused on bacteria that affect the physiology and ecology of microalgae such as survival and sexual reproduction. In the Japanese coastal sea areas such as Harima-Nada, the giant diatom Coscinodiscus wailesii can cause serious damage to Nori (Porphyra) culture during the autumn and following spring. A marine bacterium Alteromonas sp., lethal to C. wailesii, was isolated from eastern Seto Inland Sea, Japan. The existence of bacteria that induce sperm formation in this diatom was also confirmed in the coastal area. To try to regulate those harmful algal blooms by microorganisms, the interactions between these bacteria and microalgae have been investigated. Namely, the lethal processes, the algicidal ranges, the effects of incubation conditions such as temperature, irradiance, cell densities of bacteria on these bacterial activities, and the chemicals produced by bacteria were studied. These studies strongly suggest that these bacteria play an important role in the development and decomposition of algal blooms, and in the usual succession of microalgal community structures. Since, there is a possibility of controlling the occurrence and extermination of these harmful algal blooms such as C. wailesii, the efforts should be offered to investigate these microorganisms.