Effect of anaerobic conditions in bottom waters on the occurrence of red tides at omura bay.

The field observation that the occurrence of red tides at Omura Bay may have a close connection with the development of anoxic conditions in bottom waters was tested by bioassays of seawater collected during summer 1971. The stimulating effect of anaerobically-decomposed products of bottom mud on the growth of Gymnodinium type-'65 was examined. The results suggest that the development of oxygen deficiency in the bottom waters of Omura Bay makes the environment favourable for the growth of red tide organisms, both by the supply of inorganic nutrients and of some unidentified stimulants.