Management of urban wetlands for conservation can reduce aquatic biodiversity and increase mosquito risk

Global wetland loss means constructed urban wetlands are an increasingly valuable resource for conservation. However, priorities for managing urban wetlands for conservation are often seen to conflict with management to reduce potential mosquito risks, such as nuisance biting and pathogen transmission. Understanding the ecological consequences of wetland management practices is vital to maximize the conservation value of urban wetlands without negatively impacting public health; however, management practices are often untested. We conducted a landscape-scale experiment to test the ecological impacts of an existing urban wetland management regime, in which a group of urban wetlands are drained annually to reduce the abundance of an invasive fish, the plague minnow Gambusia holbrooki, and then refilled to provide breeding habitat for a threatened frog, the green and golden bell frog Litoria aurea. We collected and compared aquatic macroinvertebrates and mosquito larvae from these refilled wetlands, and adjacent undrained wetlands, as well as sampling adult mosquito populations on four occasions across summer and autumn. Wetland draining had a significant effect on aquatic macroinvertebrates and larval mosquitoes. Twice as many macroinvertebrates were collected from drained wetlands compared to undrained wetlands, and almost all mosquito larvae were collected from drained wetlands. Differences in macroinvertebrate assemblages and larval mosquitoes at drained and undrained wetlands decreased over time, but total macroinvertebrate abundance and taxa richness did not. Synthesis and applications. While conserving threatened habitats and species is vitally important, our results highlight how wetland management practices can unintentionally impact non-target species, and potentially public health. As constructed urban wetlands become more common, so too does the need for routine maintenance and management of threatened and invasive species. It is essential that future design and management of urban wetlands considers the impact mosquitoes might have on humans. Pre-emptive action to control geographically relevant vectors of mosquito-borne pathogens and nuisance biting species would reduce human exposure to mosquitoes and associated negative impacts, and increase positive conservation outcomes associated with urban wetlands.