Invasive plant-induced shifts in water chemistry and microeukaryotes enhance mosquito development

Invasive non-native plants can cause ecological, economic, and health impacts worldwide, yet how these impacts cascade from a primary producer to multiple consumers remains poorly understood. Using aquatic microcosms, we examined how replacing the native reed Phragmites australis with the morphologically similar invader Arundo donax (0–100% leaf litter biomass gradient) alters water physicochemistry, microeukaryote assemblages, and the development of Culex pipiens mosquito larvae in northeastern Spain. Microeukaryotes are key players in microbial food webs, and mosquito larvae are microbial consumers. Increased A. donax leaf litter % disrupted microeukaryote taxonomic composition and functional guild structure, mainly due to changes in the density of flagellates, planktonic ciliates, and micrometazoa. Mosquito larval development was mainly driven by changes in water physicochemistry, flagellates, and amoebae. Microcosms with A. donax produced more mosquito pupae of greater weight and shorter development times. Effects emerged even when only 25% of P. australis biomass was replaced by A. donax , suggesting potentially strong nutrient limitations from P. australis leaf litter and posing challenges for defining a management “safe threshold” for A. donax when eradication is unfeasible. This study highlights A. donax leaf litter as a potential promoter of mosquito development and underscores the role of water chemistry and microeukaryotes in mediating its effects.