Snail communities increase submerged macrophyte growth by grazing epiphytic algae and phytoplankton in a mesocosm...

The relationships between producers (e.g., macrophytes, phytoplankton and epiphytic algae) and snails play an important role in maintaining the function and stability of shallow ecosystems. Complex relationships exist among macrophytes, epiphytic algae, phytoplankton, and snails. We studied the effects of snail communities (consisting of Radix swinhoei, Hippeutis cantori, Bellamya aeruginosa, and Parafossarulus striatulus) on the biomass of phytoplankton and epiphytic algae as well as on the growth of three species of submerged macrophytes (Hydrilla verticillata, Vallisneria natans, and one exotic submerged plant, Elodea nuttallii) in a 90-day outdoor mesocosm experiment conducted on the shore of subtropical Lake Liangzihu, China. A structural equation model showed that the snail communities affected the submerged macrophytes by grazing phytoplankton and epiphytic algae (reduction in phytoplankton Chl-a and epiphytic algal abundance), enhancing the biomass of submerged macrophytes. Highly branched macrophytes with high surfaces and morphologies and many microhabitats supported the most snails and epiphytic algae (the biomass of the snail communities and epiphytic algae on H. verticillata was greater than that on V. natans), and snails preferred to feed on native plants. Competition drove the snails to change their grazing preferences to achieve coexistence.