Ecological Risk Screening Summary - Common Ball Waterflea (Chydorus sphaericus) - Uncertain Risk

Chydorus sphaericus s. str. is a cladoceran species that is native to western Eurasia and Greenland. C. sphaericus s. str. has been introduced to South Australia, perhaps through fish stocking programs, and in South Korea. No impacts of these introductions have been reported. The History of Invasiveness for C. sphaericus s. str. is classified as Data Deficient due to uncertainties in the species’ range and the lack of documented impacts of its introduction. The climate matching analysis for the contiguous United States indicates establishment concern for this species. The climate match was mostly medium across the contiguous United States with areas of high match in the northern Great Lakes, Northern Plains, and Western Mountains. The Certainty of Assessment for this ERSS is classified as Low because of the lack of information regarding impacts of the introductions and the difficulty in interpreting available information and the history of taxonomic redescription. The Overall Risk Assessment Category for C. sphaericus in the contiguous United States is Uncertain.

Species that are considered uncertain risk need a more in-depth assessment beyond the Risk Summary to better define the species’ risk to U.S. environments.