Determining Water Depths for Monitoring Coastal Water Quality Using Multiple Functional Traits of Periphytic Protozoa in Marine Ecosystems

Biological trait analysis (BTA) of protozoan communities has been used a useful bioindicator of environmental quality status in marine ecosystems. To determine the optimal water depths for bioassessment using multiple functional traits of periphytic protozoa, community functioning was studied at different water depths in the Yellow Sea, northern China. The community-weighted means (CWM) of bacterivores with small sizes showed an increasing trend from surface layers to the deeper ones, while those of algivores with medium and large sizes revealed an opposite trend, i.e., a decreasing trend from surface layers to deeper ones. However, with those of predators were distributed at depths of 2 to 3.5 m. There was a significant difference in the functional patterns, except for those at depths of 2 to 3.5 m (P > 0.05). All diversity indices except FDiv generally peaked and leveled off at either 2 or 3.5 m although they decreased with depth. The results suggest that sampling at depths of 2 and 3.5 m may be an optimal strategy for assessing water quality using the functional pattern of protozoa in coastal ecosystems.