Ecological Risk Screening Summary - Dark Falsemussel (Mytilopsis leucophaeata) - Uncertain 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.

Mytilopsis leucophaeata, Dark Falsemussel, is a mollusk native to the brackish systems in the Gulf of Mexico and the Atlantic coast of North America. The native and introduced distributions of M. leucophaeata span tropical, subtropical, and temperate climates. Populations often occur in benthic, brackish waters across wide temperature and salinity ranges. Salinity levels of 0 ppt were observed to result in complete mortality of embryos. Introductions have occurred through transport in ship ballast water and “hitchhiking” via hull and marine equipment fouling. The History of Invasiveness for Mytilopsis leucophaeata is classified as High due to records of established nonnative populations and resulting negative impacts within these systems. M. leucophaeata is a known fouling species, blocking pipes and cooling systems of industrial facilities and covering boat hulls. The climate matching analysis for the contiguous United States indicates establishment concern for this species outside its native range. The highest matches occurred in its native range along the Atlantic Coast and Gulf of Mexico and expanded north along the Atlantic Coast and into the interior eastern areas of the contiguous United States. Due to salinity requirements for survival of larvae, the climate matching analysis refers only to where the species can survive and not necessarily to where it can reproduce. The Certainty of Assessment for this assessment is classified as Medium due to the uncertainty regarding areas where the species can reproduce and establish nonnative populations. The Overall Risk Assessment Category for Mytilopsis leucophaeata in the contiguous United States is Uncertain because the salinity required for the species’ reproduction may limit establishment in many inland locations. In areas where both climate and salinity are adequate for establishment, this species may be considered high-risk.