113 - The unexpected effects of sea level rise on ‘freshwater’ mosquitoes

Abstract: Jordy van der Beek, Charlotte Linthout, Tessa Visser, Sam Boerlijst, Koos Biesmeijer, Sander Koenraadt, Reina Sikkema, Maarten Schrama

Climate change is reshaping the entire environmental landscape thereby impacting biodiversity, including mosquitoes. These impacts go beyond just temperature and precipitation. The droughts and sea level rise associated with climate change are drastically altering the environmental landscape, pushing coastal areas – such as low-lying deltas and islands – towards increasingly saline environments. The effects are already ubiquitous in the coastal landscape of NW-Europe, where we expect that the gradual salinization of former freshwater habitats deeply impacts freshwater ecosystems, leading to direct and indirect effects on mosquitoes.

The aim of this study, therefore, is to gain insight into the effects of (predicted) increases in salt concentrations on mosquito community composition, mortality, vitality, and vector competence. We collected larvae of different species across a salinity gradient in the Netherlands and exposed Culex pipiens to different salt concentrations in an experimental set-up.

Our results demonstrate that many species that are assumed to be freshwater species, such as West Nile virus vectors Culex pipiens and Culex modestus, do occur naturally under brackish conditions. Furthermore, we show that salt concentrations up to 50% seawater hardly affect Culex pipiens in terms of mortality, development time, longevity, and vector competence. However, it is likely that most predators of mosquito larvae, such as predaceous diving beetles and backswimmers, will not be able to survive under such conditions. Overall, our results suggest that some freshwater mosquito species may exhibit much higher salt tolerance than conventionally assumed.

The absence of major effects on mosquitoes, combined with a decrease in predators, may lead to higher mosquito abundances in places that are salinizing. These findings highlight the potential impacts of salinization on mosquito populations and on pathogens they transmit in coastal areas.