Community structure and seasonal dynamics of planktonic ciliates along salinity gradients

The ciliate community structure and seasonal dynamics in a solar saltern of the Yellow Sea were studied based on 4 sampling dates and 8 stations with salinities from 27.7‰ to 311.0‰. The effects of the type and concentration of the fixative used (Lugol's and Bouin's) were tested at the first sampling date. Fixative type and fixative concentration had significant effects on ciliate abundance and biovolume, with 1% Lugol's giving the best results. A detailed investigation using live observations and protargol staining techniques revealed a total of 98 morphospecies from 8 sampling stations. There was obvious seasonal variation in species composition at most of the stations, but this tended to be less distinct with increasing salinity, as the dominant ciliate group shifted from oligotrichs to heterotrichs. Ciliate abundance varied from 4.40×101 to 2.11×105 cells l−1 and biomass ranged between 2.39 and 9.87×103 μg C l−1 (at a salinity of 147.6‰). Both abundance and biomass decreased abruptly when salinity exceeded 100–150‰. Statistical analyses suggested that the dynamics of ciliate abundance and biomass were regulated by both salinity and by season, but those of diversity and species richness were mainly controlled by salinity and both significantly decreased with increasing salinity.