Can the freshwater snail Bellamya aeruginosa (Mollusca) affect phytoplankton community and water quality?

The purpose of this microcosm experiment was to determine whether the freshwater snail Bellamya aeruginosa affected phytoplankton community and water quality. Three treatments of different snail densities (low, medium, and high) and a control (no snails) were set up in twelve enclosures. Chlorophyll a (chl a ), transparency (SD), water temperature (WT), dissolved oxygen (DO), pH, nutrients, and abundance of phytoplankton were determined on days 0, 3, 7, 11, 15, 23, 31, 46, and 61. The total chl a concentration decreased and SD increased in the treatments, whereas the proportion of cyanobacteria chl a increased. Bellamya seemed to result indirectly in a decrease of DO, by reducing the algal biomass rather than by respiration. A significant decrease in nitrogen–phosphorus ratios was observed in the treatments. In the enclosed system the abundance of colonial green algae decreased over time whereas that of cyanobacteria and flagellates increased. Principal response curves showed that both phytoplankton community and water quality in the medium and high-density treatments were consistently different from in the control. These results indicate that the presence of snails resulted in a significant change of water physicochemical properties and phytoplankton community.