Can functional units of periphytic protozoan communities be used to evaluate the effects of harmful algal blooms on ecological quality in marine ecosystems?

Based on biological traits, the ecological quality status under the pressure of two harmful algal bloom (HAB) species was evaluated using functional units (FUs) of periphytic protozoan communities. Five treatments with different concentrations of Alexandrium tamarense and Gymnodinium catenatum, i.e., 10 0 , 10 2 , 10 3 , 10 4 , and 10 5 cells ml -1 , were used. A total of 20 FUs were identified from 25 test protozoan species. Among these FUs, vagile algivores with large sizes showed a decreasing trend (i.e., in diversity and abundance) with increasing concentrations of algae, while vagile bacterivores and non-selectives with small sizes dominated at concentrations of 10 4 cells ml -1 of both algal species. Ellipse tests on pair-wise functional distinctness indices revealed a significant departure of test protozoan communities from an expected functional distinctness breadth when algal concentrations exceeded 10 4 cells ml -1 . Based on these findings, it was concluded that FUs of periphytic protozoa may be a useful tool for evaluating the effects of HABs on ecological quality status in marine ecosystems.