Seasonal variation in the species composition of tintinnid ciliates in

Abstract. Seasonal changes in the species composition of tintinnid ciliates were examined based on time-series samples taken at 2 week intervals over a 3 year period in Hiroshima Bay, the Seto Inland Sea of Japan. The maximum abundance of total tintinnids over the entire period was 5.7 X 103 indi-viduals 1"'. Among 32 species identified, a consistent seasonal occurrence was recognized in 22 species. The relationships between various environmental factors and the abundance of each species of tintin-nids were analyzed using principal component analysis. From this analysis, the abundance of many tintinnids was revealed to be associated with temperature, the <20 prni size fraction of chlorophyll a and water column stability, but not with the>20 u.m size fraction of chlorophyll a, nor with salinity. From these results, tintinnid species were divided into five association types: species whose abundance increased with increasing temperature, decreasing temperature, nanophytoplankton abundance, increasing water column mixing, or increasing water stratification coupled with low temperature