Invasion of the New Zealand mud snail (Potamopyrgus antipodarum) in the Green River below Flaming Gorge Dam

Abstract

New Zealand mud snails (Potamopyrgus antipodarum) were first introduced to the United States in 1987 and have subsequently invaded water bodies across the United States. At high densities, P. antipodarum can outcompete native fauna, disrupt community interactions, and alter ecosystem function, making them a threat to aquatic habitats worldwide. In this paper, we detail the invasion, population dynamics, and secondary production of P. antipodarum at seven sites in the Green River below Flaming Gorge Dam (0.8–49 km below the dam). New Zealand mud snails were first detected in the Green River in 2001. For more than a decade, densities of P. antipodarum in the Green River remained relatively low (< 1200 individuals m⁻²) at all sites. However, in 2015 densities started to increase dramatically at three sites below the dam, eventually reaching > 19,000 individuals m⁻². Annual secondary production estimates of P. antipodarum for the year 2016 ranged from < 0.1 g m⁻² yr⁻¹ to 14.2 g m⁻² yr⁻¹. Furthermore, in terms of production, P. antipodarum was one of the dominant invertebrate taxa at six of the seven sites. Why densities dramatically increased after 2015 at only three of the seven sites remains unclear. Moreover, it is currently unknown whether populations of P. antipodarum in the Green River will undergo a “bust” period following their dramatic increase in density like populations of P. antipodarum in other river systems. Nevertheless, given the recent increases in densities of P. antipodarum and the relatively high rates of production at several sites, we recommend continued monitoring and suggest that attention be brought to the potential effects of New Zealand mud snails on the structure and function of the Green River ecosystem.