Permalink : http://hdl.handle.net/2115/49096

KEYWORDS : Red tide;Prevention;Killer bacteria;Algicidal bacteria;Ulva pertusa;Seaweeds;Poly-culture

Seasonal fluctuations of algicidal bacteria were investigated with the microplate MPN method in surface seawater and on the surface of the green alga Ulva pertusa in cage culture for poly-culture at the stations in Shimo-Haya Bay, Wakayama Prefecture.　Target red tide species were three raphidophytes of Chattonella antiqua, Heterosigma akashiwo and Fibrocapsa japonica, and two dinoflagellates of Karenia mikimotoi and Heterocapsa circularisquama.　In seawater, most part of killer microorganisms was substantially algicidal bacteria, and the most abundant killer bacteria were killers for Karenia mikimotoi and followed by killers for Fibrocapsa japonica.　The maximum value was 2.2×10^4 MPN ml^-1 for K. mikimotoi killers.　On the surface of U. pertusa, K. mikimotoi killers were also most abundantly detected with a maximum value of 1.1×10^6 MPN g^-1 (wet weight) and F. japonica killers also showed a high value of 1.9×10^5 MPN g^-1 (wet weight).　Isolation of killer bacteria after colony formation and co-culture experiments, K. mikimotoi killers and F. japonica killers also displayed high abundances, and other killers such as C. antiqua killers were detected with rather high values of 10^4～10^5 cells g^-1 (wet weight).　Poly-culture of seaweeds and fishes is not only environment friendly in aquaculture but also useful sources for preventing harmful red tides in the coastal sea.