The red tide that appeared in the coastal area of Fukuyama, June 1966, was caused by the microscopic dinoflagellate Entomosigma sp. Since this red tide came after rainfall, it was implied that the organism might prefer low salinities and perhaps nutrients washed into the sea from the land. From this hypothesis, laboratory culture was started.
Entomosigma sp. was obtained in axenic culture by micropipette washings. The organism prefers slightly low salinity (Cl 16.0‰), yet, tolerates a wide range of salinities. The growth is accelerated by the trace metals and/or the weak chelator, nitrilotriacetic acid, to sea water. Supplement of nitrogen and phosphorus sources to sea water favors growth. Entomosigma sp. needs vitamin B12 for growth. The pattern of specificity is similar to that of Ochromonas malhamensis. All the analogues containing benzimidazole can replace B12 • These results seem to substantiate the above hypothesis.