Calcium concentrations in the lower Columbia River, USA, are generally sufficient to support invasive bivalve spread

Dissolved calcium concentration [Ca²⁺] is thought to be a major factor limiting the establishment and thus the spread of invasive bivalves such as zebra (Dreissena polymorpha) and quagga (Dreissena bugensis) mussels. We measured [Ca²⁺] in 168 water samples collected along ~100 river-km of the lower Columbia River, USA, between June 2018 and March 2020. We found [Ca²⁺] to range from 13 to 18 mg L⁻¹ during summer/fall and 5 to 22 mg L⁻¹ during the winter/spring. Previous research indicates that [Ca²⁺] < 12 mg L⁻¹ are likely to limit the establishment and spread of invasive bivalves. Thus, our results indicate that there is sufficient Ca²⁺ in most locations in the lower Columbia River to support the establishment of invasive dreissenid mussels, which could join the already widespread and abundant Asian clam (Corbicula fluminea) as the newest invader to an already heavily invaded Columbia River ecosystem. These new data provide important measurements from a heretofore undersampled region of the Columbia River and have important implications for the spread of invasive bivalves and, by extension, the conservation and management of native species and ecosystems.