Ecological Risk Screening Summary - Thick Scud (Obesogammarus crassus) - High Risk

Species that are considered high risk have a well-documented history of invasiveness in at least one location globally, and a high or medium climate match to the contiguous United States.

Obesogammarus crassus, thick scud, is an amphipod that is native to the Ponto-Caspian basin of Europe. O. crassus has an omnivorous diet and can tolerate a range of oxygen levels, temperatures, and salinities. O. crassus is generally moved between water bodies via ballast water transport, and there were reports of its historical use as a stocked food source for fish. The History of Invasiveness for O. crassus is classified as High due to known, nonnative, established populations that have competed with native amphipod species with a negative outcome for the native species. The climate matching analysis for the contiguous United States indicates establishment concern. The highest matches occur in the Great Lakes Basin and along the Rocky Mountains and Great Basin. The Certainty of Assessment for this ERSS is classified as Medium due to a limited amount of available research and knowledge regarding impacts. The Overall Risk Assessment Category for Obesogammarus crassus in the contiguous United States is High.