Recent Evaluation of Corbicula Form D Distribution in the Midwest, USA

The genus Corbicula contains one of the most common and successful aquatic invasive species to North America. Prior to 2015 two predominant species of Corbicula were known from the United States-C. fluminea and C. largillierti, referred to as Forms A and B, respectively. Form A has spread throughout most of the U.S., while Form B is mainly contained in the Midwest and southern U.S. In 2015 a novel Corbicula, known as Form D, was discovered in the Illinois River, at Marseilles, Illinois, and was later reported from the Ohio River. Our primary objective for this study was to report additional records of Form D, with a focus on the upper Illinois River watershed. Surveys during summer 2017 verified the presence of Form D in the Tennessee and Mississippi rivers, as well as multiple new locations in the Des Plaines and Illinois rivers, where all three Corbicula forms co-exist.