Insights into the effects of harmful algal bloom on ecological quality status using body-size spectrum of biofilm-dwelling ciliates in marine ecosystems.

Abstract The effects of two harmful algae Alexandrium tamarense and Gymnodinium catenatum on ecological quality status were identified using biofilm-dwelling ciliate assemblage as test organism communities. The body-size spectra of the test ciliates were observed at a gradient of cell concentrations of both algal species: 100 (control), followed by102, 103, 104 and 105 cells ml−1. The test ciliates showed clear variations in body-size spectra along the concentration gradients of both algal species. In terms of probability density, the ciliates generally peaked at low levels of algal concentrations (100–104 cells ml−1) in small size forms, followed by the forms with large sizes at the concentration of 105 cells ml−1 of both algal species. Bootstrapped-average analysis demonstrated a significant change in body-size spectrum when algal concentrations were higher than 104 cells ml−1. It is suggested that the body-size spectrum of the ciliates may be used to indicate the effects of harmful algal bloom.