The Ponto-Caspian quagga mussel, Dreissena rostriformis bugensis Andrusov, 1897, is established in Ireland.

The quagga mussel Dreissena rostriformis bugensis was identified in a horizon scan of species likely to arrive in Ireland. We report on the first records of this dreissenid from two lakes, a reservoir and interconnecting navigable river sections on Ireland's largest river, the Shannon, during July 2021. The abundance in Lough Ree was greater than in the larger downstream lake of Lough Derg. Specimens occurred to depths of 24 m and 32 m in each of these lakes respectively. Highest densities were in the southern region of Lough Ree attached to piles supporting floating pontoons and quay walls. Here D. r. bugensis outnumbered the D. polymorpha present. It was present at lower densities downstream to Lough Derg and the Parteen Reservoir. This species has a wide range of colour morphs from a pale yellow to dark concentric or longitudinal banding. [ABSTRACT FROM AUTHOR]