Seasonal change of dinoflagellates cyst flux collected in a sediment trap in Omura Bay, West Japan

Abstract

Sediment trap samples were harvested bimonthly from 1998 to 2000 and examined to better understand the species composition and seasonal variation of dinoflagellate cyst flux in Omura Bay in Japan. Samples’ living cyst flux clearly showed seasonal variation with the higher flux number between autumn and winter. In total, 43 different cyst taxa were recorded, and these were composed of two different ecological groups. The first group included Protoperidinium compressum and Protoperidinium subinerme, which increased every autumn to winter. The second group included Gonyaulax spp. and Pheopolykrikos hartmannii and was trapped throughout the year. These two groups manifested the different flux patterns and were, respectively, heterotrophic and autotrophic in nutrition. In the heterotrophic group, protoperidinioid cysts were dominant. Vegetative cells of protoperidinioid are known to feed mainly diatoms. Sample diatom flux also increased from autumn to winter. Therefore, the increase of protoperidinioid cysts in autumn to winter was observed to correlate with diatom blooms. In contrast, the autotrophic group mostly consisted of Gonyaulacoid cysts and were generally observed throughout the year, although occurrence varied between species most likely responding to favorable environmental conditions. The results indicate that cyst production is closely related to different nutritional modes.