Use of functional distinctness of periphytic ciliates for monitoring water quality in coastal ecosystems

As trait-based ecological parameters, functional diversity/distinctness measures are robust parameters for biodiversity research by reducing “signal to noisy” ratios due to functional redundancy in a community, and have an advantage for bioassessment due to a statistical framework for testing departure from expectation by combining ecosystem functions and community structure. The effectiveness of four functional diversity/distinctness measurements for water quality assessment was based on a study of additional ciliate datasets for biological evaluation of coastal waters along the Yellow Sea in northern China. A fuzzy-coding trait system was used as a trait pool, which comprised six characters of feeding types, movement features, body size/form/flexibility, and sociability. Results showed that (1) the functional diversity (Δχ) significantly related to the spatial variation in water transparency; (2) the average functional diversity index (Δχ+) and variation in functional distinctness (Λχ+) represented a significant correlation with the changes in pH and nutrients, especially ammonium nitrogen, and soluble active phosphate; and (3) ellipse test for the paired indices (Δχ+ and Λχ+) revealed a clear departure from an expected functional trait pattern. According to our findings, it is recommended that the functional diversity/distinctness measures may be served as a robust bioindicator of water quality status in marine ecosystems.