Distribution and Fluctuation of Bacteria Inhibiting the Growth of a Marine Red Tide Phytoplankton Gymnodinium mikimotoi in Tanabe Bay (Wakayama Pref., Japan)

Abstract

Distribution and seasonal fluctuation of the bacteria which inhibit the growth of a red tide marine dinoflagellate Gymnodinium mikimotoi, were surveyed in Tanabe Bay (Wakayama Pref., Japan), using the newly developed MPN method with an axenic culture of G. mikimotoi. G. mikimotoi's growth inhibiting bacteria (Gm-GIB) were detected at 10³-10⁴ cells/ml before occurrences of huge red tides by G. mikimotoi at the beginning of August in 1990 and from the end of August to the beginning of September in 1991. The number of Gm-GIB fell by about two orders of magnitude at the blooming periods of G. mikimotoi, and then increased again after the blooms declined. These results suggest that the fluctuation of Gm-GIB counts in seawater is significantly related to the developmentand decline process of G. mikimotoi red tide. Forty strains of Gm-GIB isolated in this study all acted as killers against this dinoflagellate rather than as suppressers on the algal growth under laboratory conditions. The precise causes of the fluctuation of Gm-GIB in seawater environments remain unknown.