Insights into discriminating environmental quality status using taxonomic distinctness based on a small species pool of ciliated protozoa in marine ecosystems

The objective of this study was to determine the feasibility of developing a protocol for assessing marine water quality based on taxonomic relatedness within a small pool of planktonic ciliates. An annual dataset was compiled based on samples collected biweekly at five sites, with a gradient of environmental stress, during a 1-year cycle in Jiaozhou Bay, northern China. A total of 60 species, belonging to 17 genera 10 families, 5 orders and 2 classes of the phylum Ciliophora, were identified. Among five orders, Tintinnida showed a low variability mainly at species level whereas the other orders (especially Strombidiida and Choreotrichida, although with the exception of the genus Strombidium) represented a high variability at higher taxonomic ranks (e.g. family or order). Mantel analyses showed that spatial patterns of the ciliate assemblages, with tinitinnids and Strombidium spp. excluded, were significantly correlated with those of the total planktonic ciliate communities in terms of their response to environmental status. The average taxonomic distinctness (Δ+) based on the small species pool was significantly negatively correlated with the changes in concentrations of nutrients (P < 0.05). Furthermore, the paired indices of Δ+ and the variation in taxonomic distinctness (Λ+) showed a clear departure from the expected taxonomic pattern. These findings suggest that it is possible to assess the status of marine water quality using the taxonomic relatedness within a small pool of planktonic ciliates.