This study investigates the effects of nano-polystyrene (nano-PS) on the growth and reproduction of the green alga *Scenedesmus obliquus* and the zooplankton *Daphnia magna*. Nano-PS exposure reduced the growth and chlorophyll concentrations in *S. obliquus*, while *D. magna* showed reduced body size and severe alterations in reproduction, including a decrease in neonate production and an increase in malformations. The malformation rate reached 68% among neonates exposed to aged nano-PS at concentrations of 32 mg/L. These effects were observed at concentrations much higher than those typically found in marine or freshwater environments but may occur in sediment pore waters. The study provides the first evidence of direct life history shifts in algae and *D. magna* populations due to nanoplastic exposure, highlighting the need for further research on the ecological impacts of nanoplastics.This study investigates the effects of nano-polystyrene (nano-PS) on the growth and reproduction of the green alga *Scenedesmus obliquus* and the zooplankton *Daphnia magna*. Nano-PS exposure reduced the growth and chlorophyll concentrations in *S. obliquus*, while *D. magna* showed reduced body size and severe alterations in reproduction, including a decrease in neonate production and an increase in malformations. The malformation rate reached 68% among neonates exposed to aged nano-PS at concentrations of 32 mg/L. These effects were observed at concentrations much higher than those typically found in marine or freshwater environments but may occur in sediment pore waters. The study provides the first evidence of direct life history shifts in algae and *D. magna* populations due to nanoplastic exposure, highlighting the need for further research on the ecological impacts of nanoplastics.