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The outcome of multiple invasions from a common origin may lead to facilitative interactions because the invaders have co-evolved under similar environmental conditions. This outcome is often referred to as invasional meltdown, with a resultant increase in invasive species and a decline in native species richness and abundance., This study seeks to assess the full scope of the threat posed by a high-risk group of 23 freshwater invaders originating from the Ponto-Caspian region (south-east Europe) across Great Britain. Ponto-Caspian invaders constitute a group of special concern because they have recently caused a large-scale invasion into western Europe., According to a literature review, 76% of reported interactions between Ponto-Caspian invaders are positive (mostly provision of food and commensalism) or neutral (habitat partitioning). Negative interactions (mostly predation) were rare, thus highlighting the ability of Ponto-Caspian invaders to coexist., At least 14 out of the 23 Ponto-Caspian organisms investigated are well-established in the Rhine estuary and Dutch ports. Four of them ( Hemimysis anomala, Dikerogammarus villosus, D. haemobaphes and Hypania invalida) have recently established in Great Britain. Regression models suggest the rest are under a critical risk of being transported, with four species predicted to have arrived already to Great Britain: Echinogammarus ischnus, Jaera istri, Limnomysis benedeni and D. bispinosus., According to species distribution models, the cumulative risk of invasion of multiple Ponto-Caspian species, thus invasional meltdown, is highest in the south-east of England and decreases to the north and west., Great Britain might be on the brink of invasional meltdown, and as a consequence, confronting the problem of Ponto-Caspian invasive species is a vital element for national biosecurity., Synthesis and applications. The predictive models and maps developed in this study provide a means for an evidence-based prioritization of species and habitats for the management of existing and future invasions of Ponto-Caspian species. This integrated approach can be easily applied to risk assess other groups of species and habitats. [ABSTRACT FROM AUTHOR]

The expansion of Invasive Alien Species (IAS) is a growing concern to the UK water industry because of their diverse impacts on water quality, infrastructure and eradication costs. New regulations reinforcing the industry's responsibilities beyond operational costs, coupled with continued range expansion and establishment of new IAS will increase damages. To tackle IAS effectively, the water industry requires reliable information about which species pose the greatest risk to operations and which areas are most vulnerable to invasion. Here we assess potential biosecurity threats for the 24 water companies in the UK using well-established modelling research techniques such as risk assessment and distribution modelling. Using a consensus approach with environmental managers and water companies, we identified 11 IAS of concern for the UK water industry, including five plants, three crustaceans, two molluscs and one fish. These invaders pose important hazards in terms of water quality, flood protection, human health, integrity of infrastructures, recreational and aesthetic values, amongst others. We used distribution models to predict their potential expansion under current and future 2050 climate scenarios within each of the 24 water companies in the UK. Water companies in the South East of England (Cambridge Water, Anglian Water, Affinity Water and Thames Water) are under the highest risk of invasional meltdown from multiple IAS, both now and under future scenarios. The quagga mussel poses the most serious risk of immediate spread and may exacerbate the impacts of the widespread zebra mussel for the water industry. The information generated in this study can support the prioritization of species and regions at risk, so that funds for prevention and eradication of invasions are well allocated. Ultimately, this study demonstrates that scientific risk assessments, usually restricted to the academic and public sectors, can be extremely useful to guide decision-making by the private sector. Image 1 • Invasive Alien Species cause important changes in water quality. • We identified 11 IAS of concern to the water industry through a consensus approach. • We modelled their potential expansion under current and future climate scenarios. • Water companies in the SE of England will bear the highest costs of control of IAS. • Our approach can cost-effectively prioritize species and regions at risk. [ABSTRACT FROM AUTHOR]