Combined effects of invasive mosquitofish and invasive red swamp crayfish in small aquatic ecosystems

Authors: Fryxell, David*, Diluzio, Amber, Friedman, Maya, Menge, Nicklaus, Palkovacs, Eric

Year: 2015 (xlvii)

Abstract

Invasive species are a threat to native biodiversity and can change important aspects of ecosystem function. Many ecosystems have been invaded by two or more non-native species, making it important to evaluate how interactions among invaders shape communities and ecosystem processes. Two common invaders in aquatic systems of the American Southwest are the western mosquitofish (Gambusia affinis) and the red swamp crayfish (Procambarus clarkii), both of which have been studied considerably in independence. Evidence from their nonnative range suggests these species may interact with one another, but what does this mean for their community- and ecosystem-level impacts in sympatry? Using experimental ponds, we tested for the community and ecosystem effects of crayfish and mosquitofish independently and together to understand their additive and interacting effects. As expected based on prior work, mosquitofish induced a strong pelagic trophic cascade by reducing the abundance of pelagic phytoplanktivores, and crayfish increased water conductivity and sedimentation, likely through bioturbation associated with detrital processing. Interestingly, crayfish increased pelagic Daphnia abundance, perhaps by increasing their food resources or excluding them from the benthos. In sympatry, the species effects were almost exclusively additive with the exception of their effect on snail abundance; mosquitofish increased snail abundance, crayfish decreased snail abundance, but both species together had the lowest snail abundance of all treatments. Such interacting effects are difficult to predict without experimentation, but are important to our understanding of the impact of multiple sympatric invasives.