Harmful cyanobacterial blooms and taste-and-odor control: Synergistic effects of submerged macrophytes and freshwater snails

Harmful cyanobacterial blooms and 2-methylisoborneol (2-MIB) episodes are major challenges faced by eutrophic lakes and reservoirs. This study investigated the effects of submerged macrophytes ( Myriophyllum spicatum ) and freshwater snails ( Bellamya aeruginosa ) on the growth of Pseudanabaena and the release of 2-MIB both in the field and in the laboratory. Field data from the Yangtze River estuary revealed lower cyanobacterial biomass and odorants in macrophyte-snail habitats compared to phytoplankton-dominated areas. Co-culture experiments demonstrated that snail-only treatments inhibited Pseudanabaena biomass up to 96 %–100 % through grazing and secretions, outperforming macrophyte-only treatments (46 % inhibition via nutrient competition and allelopathy). Notably, their combination produced synergistic effects, integrating snail grazing with macrophyte allelopathy for more efficient and stable suppression. The snail secretions selectively inhibited the photosynthetic activity and biomass of Pseudanabaena . The synergistic effects were density-dependent: optimal snail density (180 ind m −2 ) achieved highest cyanobacterial suppression while boosting macrophyte biomass by 34.9 % through epiphyton control and nutrient recycling. Our study proposes that snails in Myriophyllum stands reduce the biomass of Pseud anabaena as well the concentration of 2-MIB in water. • First demonstration of macrophyte-snail joint effects on filamentous cyanobacteria. • Lower 2-MIB observed in macrophyte-snail symbiotic habitats than phytoplankton-dominated habitats. • The snail secretions selectively inhibit the photosynthetic activity of Pseudanabaena. • Optimal snail density (180 ind·m −2 ) enhances macrophyte biomass by 34.9 %.