Artificial substrate experiments to investigate potential impacts of invasive quagga mussel (Dreissena rostriformis bugensis, Bivalvia: Dreissenidae) on macroinvertebrate communities in a UK river.
Predicting potential impacts of a new invasive species remains difficult. A group of particular concern in the UK are freshwater invertebrates from the Ponto-Caspian region, including the recently established quagga mussel (Dreissena rostriformis bugensis, Bivalvia: Dreissenidae). We explored invertebrate colonisation across a series of manipulated substrate tiles with gradated densities of D. r. bugensis shells fixed to their surface (2220, 1111, 666, 222 and 0 individuals m-2). Across three experiments of different substrate tile deployment duration (14, 30 and 62 days), we observed significant differences in invertebrate density and richness among shell density treatments. Variation was primarily driven by low and high values on our control and highest substrate shell treatments, respectively. Within each experiment, similar taxa appeared to benefit from the physical effects of D. r. bugensis shells (e.g. Gammarus pulex, Chironomidae spp., Elmidae spp. and Hydropsyche spp.) being found with greater abundance on substrate tiles with higher D. r. bugensis shell treatments. Compared to invertebrate density, the response of taxonomic richness was weaker and only significant within our 30 and 62 day experiments of longer substrate tile deployment duration. Regardless, increased invertebrate density and richness across the highest shell treatments provided a strong indication of potential D. r. bugensis impacts on macroinvertebrates in the study river. If mussel densities were to increase to equivalent levels in other UK rivers, we could expect similar impacts to benthic fauna. While the likelihood of D. r. bugensis achieving such population densities are uncertain in such environments, our results were considered conservative because they did not account for additional facilitative impacts associated with live mussels. We add that, in the context of invasive species management, potential facilitation of native benthic fauna associated with D. r. bugensis in the UK should not be considered positively, nor necessarily sustainable over longer time periods. Further, facilitative effects could assist the establishment of other invasive invertebrates such as amphipods of Dikerogammarus spp., which were first recorded in the study river during this investigation.