Assessing the ecological role of the invasive clam Corbicula fluminea in southeastern rivers and nationwide
McDowell, William Giles
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Globally, ecosystems are facing myriad stressors, and climate change and invasive species are two of the most pervasive. Not only does the impact of each stressor need to be understood singly, but their interactions may produce novel, unexpected results. The impact of an invasive species is a function of its range, abundance, and effects. We examined the impact of an abundant and widespread invasive species, the freshwater clam Corbicula fluminea, by examining its range, abundance, and effects, and how these could be impacted by interactions with climate change. To understand the range of Corbicula, we used two species distribution modeling approaches: a logistic regression and Maximum Entropy modeling. Logistic regression indicated that climate was more important than habitat in controlling Corbicula’s distribution, and both models identified minimum temperature as the most important controller of Corbicula’s distribution. Applying the Maximum Entropy model to future climate scenarios showed large expansions of Corbicula’s range into New England and the northern Midwest. Thus, the impacts on rivers from climate change will be compounded by the addition of Corbicula and its own influences on ecosystem function. To estimate density and the impacts of Corbicula in the Georgia Piedmont, systematic sampling was used in four rivers spanning three of the four major watersheds in Georgia. Overall, densities ranged from 60/m2 to 175/m2, and published filtration, sedimentation, and excretion rates indicate that Corbicula play an important role in these ecosystems. The impact of Corbicula may be impacted by the occurrence of extreme events. During the summer of 2012, which was hot and dry, a mass mortality event occurred where over 99% of the Corbicula in a section of the Broad River died. As Corbicula is the only filter-feeding bivalve in the system with significant biomass, this event led to the near complete halting of the ecosystem services provided by bivalves. The clam population recovered within a year. Overall, Corbicula is having a large impact on aquatic ecosystems in the southeast. The impacts in this region could provide estimates for future scenarios in northern parts of the United States, as Corbicula’s distribution spreads with warming winter temperatures.