Nano-polystyrene influences energy flow dynamics in stream brown-green food chains: Evidence from feeding preference shifts of a river snail

Nanoplastics pose significant threats to aquatic food webs, yet their impact on energy flow dynamics between brown-green food chains remains poorly understood. This study investigated how nano-polystyrene (nano-PS; 0, 1, 10, and 100 μg·L) affected the nutritional quality of leaf litter (Populus nigra) and benthic algae (Spirogyra sp.), and further influenced the feeding preference of the river snail (Cipangopaludina cathayensis) through a 21-day microcosm experiment. Results revealed that nano-PS induced concentration- and time-dependent changes in the basal resources. Notably, exposure to 10 μg·L of nano-PS temporarily increased the quality of leaf litter by enhancing extracellular enzyme activities on day 7. However, exposure to 100 μg·L resulted in a significant decline in nutritional quality and a 53.59% increase in fungal biomass. Benthic algae exhibited an acute compensatory response under nano-PS stress but experienced chronic reductions in both biomass and nutritional quality. Furthermore, exposure to nano-PS caused oxidative stress in C. cathayensis, leading to trade-offs in energy allocation between antioxidant defense and foraging behavior. As a result, the river snail shifted its feeding preference from algae to leaf litter on day 7, but reversed this trend by day 21. Principal component analysis confirmed that the quality of available resources and the physiological status of the river snail together influenced these preference adjustments. Results demonstrated that nanoplastics disrupt energy flow in brown-green food chains by altering resource characteristics and detritivore behavior, providing crucial insights into the ecological risks posed by nanoplastics in stream ecosystems.