Artificial light at night and an invasive snail synergistically enhance the invasion of a non-native macrophyte

Herbivory shapes plant invasion outcomes, yet its role in aquatic plant invasions under changing environmental conditions, such as artificial light at night (ALAN), remains poorly understood. We conducted three experiments using invasive macrophyte Myriophyllum aquaticum, a native macrophyte community (Vallisneria natans, Hydrilla verticillata, M. spicatum), invasive snail Pomacea canaliculata, and native snail Cipangopaludina chinensis to test the combined effects of ALAN and herbivory on non-native macrophyte invasions. ALAN increased M. aquaticum height and total biomass, but had no effect on native species growth. In feeding assays, P. canaliculata consumed all three native species but consistently avoided M. aquaticum under both light treatments. C. chinensis showed no feeding in no-choice assays, but in choice assays, consumed H. verticillata and M. spicatum under No-ALAN and only M. spicatum under ALAN. In community mesocosms, P. canaliculata reduced native macrophyte biomass by 48.0% under No-ALAN and 87.2% under ALAN without affecting M. aquaticum. This selective feeding increased M. aquaticums proportional biomass, with a stronger effect under ALAN than No-ALAN. These results suggest that ALAN can indirectly facilitate non-native macrophyte invasion by amplifying their relative biomass within native communities, particularly in the presence of invasive herbivores, and may promote invasional meltdown through altered feeding preferences.