CYSTS OF THE RED TIDE FLAGELLATE HETEROSIGMA-AKASHIWO, RAPHIDOPHYCEAE, FOUND IN BOTTOM SEDIMENTS OF NORTHERN HIROSHIMA BAY, JAPAN

Cysts of the red tide flagellate Heterosigma akashiwo (Raphidophyceae) were found for the first time from surface sediments collected in nor thern Hiroshima Bay in the Seto Inland Sea, Japan. The cysts were most ly spherical with a diameter of 8.0-12.0 mum and were surrounded by mu cilaginous material to which various particles such as sand grain, mud , and pieces of diatom frustule adhered. The cysts were generally soli tary, but occasionally formed a cluster of several cysts. They were ye llow-greenish to brownish in color. The cysts do not have clumps of bl ack or dark brown materials as Chattonella cysts do. The cysts were ge nerally smaller than vegetative cells. Live cysts had auto-fluorescing chloroplasts (4-11/cyst) under blue-light excitation. The nuclei of c ysts (3.3-5.0 mum in diameter) were smaller than those of vegetative c ells. The germination occurred within a few days, mostly one or two da ys, when incubated in filtered-autoclaved seawater at 22-degrees-C wit h light.