Comparative effects of river–lake disconnection on taxonomic and functional composition of molluscan assemblages in floodplain lakes

Functional traits are promising features for biomonitoring in freshwater ecosystems. Here, we focused on 23 floodplain lakes to evaluate the responses of taxonomic and functional traits of freshwater mollusks to the loss of lateral hydrological connectivity (LHC). Our results revealed that the disconnected lakes (DLs) had significantly lower species richness of most functional trait categories of mollusks compared to the connected lakes (CLs). For percentages of species richness, only percentages of burrowers and thick-shelled species were significantly lower in DLs than CLs, while percentages of thin-shelled and small-sized species were higher in DLs. Therefore, there has been a shift toward assemblages with thin-shelled and small mollusks following LHC loss. We also found that key environmental variables affecting taxonomic and functional composition were connectivity, lake area, aquatic vegetable coverage, and water quality. Moreover, the functional composition of all Mollusca, Gastropoda, and Bivalvia were all better explained (explained variation ranged from 0.462 to 0.684) by environmental factors compacted with taxonomic composition (0.213–0.401). Connectivity was the most important factor affecting functional trait composition, whereas area was the most important variable for taxonomic composition. Thus, the trait-based approach based on mollusks was more sensitive in assessing the impacts of disconnection than the taxonomy-based approach.