Autofluorescent bodies in the toxic dinoflagellate Alexandrium tamarense: A potential indicator of the physiological condition of the species

Autofluorescent bodies were examined in cultured and natural cells of Alexandrium tamarense (Lebour) Balech collected from Ofunato Bay, Japan. Three different autofluorescent bodies (pale blue, light blue, and white) and the autofluoresced chloro- plast were observed under ultraviolet light excitation. We suggest that the pale-blue and light-blue bodies represent a novel type in dinoflagellates based on their fluorescent properties. We also found that cells with pale-blue and light-blue bodies appeared predominantly in the early and middle to late exponential phases, respectively. A similar pattern was observed in natural popu- lations during a 2-year field survey. Cells with pale-blue bodies were dominant almost one week before the bloom, whereas those with light-blue bodies were mostly apparent during the blooming stage. These results indicate that the observation of aut- ofluorescent bodies could be useful as a physiological indicator for predicting natural population blooms of A. tamarense in Ofu- nato Bay.