Dinoflagellate cyst taphonomy based on a sediment trap experiment

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1)Seasonal Change of dinoflagellate cyst fluxSediment trap samples were harvested bimonthly from 1998 to 2005 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 P.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 autumn to winter. Therefo … More re, the increase of protoperidinioid cysts in autumn to winter was observed to correlate with diatom blooms. On the other hand, autotrophic group mostly consisting of Gonyaulacoid cysts were observed throughout the year in general, however occurrence seasons of these cysts were different. Probably they can respond to favorable environmental conditions. This strongly suggested that the different behavior in cyst production is closely related to different nutrition.2)Cyst incubation experiment for establishing cyst-motile form relationshipThe heterotrophic armored dinoflagellate Protoperidinium thulesense has an unusual combination of morphological characters, i.e. the thecal plate arrangement of the motile cell resembles a typical Protoperidinium, whereas the shape and archeopyle of the cyst are like the diplopsalids. We have re-examined the cyst-motile relationship of P.thulesense by cyst incubation and thecal plate analysis together with a molecular phylogenetic study based on SSU rDNA sequences. Five isolates of P.thulesense, including motile cells and cysts from Omura Bay, and three Protoperidinium and three diplopsalid species were examined by using the single cell PCR method. The thecal plate arrangement of the motile cells isolated from field samples and those germinated from cysts were identical. The plate formula was ; Po, X, 3', 3a, 7", 3+tc, 4s, 5"', 2"". The cysts of P.thulesense were round and brown with a theropylic archeopyle, and rather similar to the diplopsalid species. Less