Blooms of toxic cyanobacteria cause the gastropod Bellamya aeruginosa to shift its diet from planktic to benthic material

Abstract

The contribution of food sources to the freshwater gastropod Bellamya aeruginosa was estimated using stable carbon and nitrogen isotope ratios in three water bodies (two reservoirs and a pond) with different history of cyanobacterial blooms in the eastern part of Zhejiang Province, China. Results of the isotope mixing model showed that filtered food materials (suspended particulate organic matter) contributed most to the diet of B. aeruginosa in both reservoirs with higher levels of chlorophyll a (chl a) in the water column, except during the summer, when a cyanobacteria (Microcystis) bloom occurred in Reservoir Tingxia. In contrast, scraped food materials (benthic detritus) contributed most to the diet of B. aeruginosa in the pond, where low levels of chl a were found in the water column. These results suggest that although filtered food materials were the main food source of B. aeruginosa when the habitat was rich in desirable suspended particles, ingestion of filtered food materials decreased during the cyanobacteria bloom. Feeding experiments were conducted to verify whether snails could avoid ingesting the cyanobacteria. The isotopic ratios in muscle tissue of B. aeruginosa fed by a diet containing only cyanobacteria were similar to those of the no‐diet treatment, implying that the snails did not feed, when only cyanobacteria were offered. Moreover, the combination of higher mortality, lower fecal pellet counts, and reduced growth (based on shell height) in the treatment with cyanobacteria indicate that B. aeruginosa stopped feeding when food became undesirable, confirming our field observations that B. aeruginosa avoids feeding on toxic cyanobacteria.