Seasonal variation in the species composition of tintinnid cilates in Hiroshima Bay, the Seto Inland Sea of Japan

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 × 103 indi viduals l− 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 tintinnids were analyzed using principal component analysis From this analysis, the abundance of many tintinnids was revealed to be associated with temperature, the <20 μm size fraction of chlorophyll a and water column stability, but not with the <20 μm 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.