Horizon scanning for invasive alien species with the potential to threaten biodiversity in Great Britain

Abstract

Invasive alien species (IAS) are considered one of the greatest threats to biodiversity, particularly through their interactions with other drivers of change. Horizon scanning, the systematic examination of future potential threats and opportunities, leading to prioritization of IAS threats is seen as an essential component of IAS management. Our aim was to consider IAS that were likely to impact on native biodiversity but were not yet established in the wild in Great Britain. To achieve this, we developed an approach which coupled consensus methods (which have previously been used for collaboratively identifying priorities in other contexts) with rapid risk assessment. The process involved two distinct phases: Preliminary consultation with experts within five groups (plants, terrestrial invertebrates, freshwater invertebrates, vertebrates and marine species) to derive ranked lists of potential IAS. Consensus-building across expert groups to compile and rank the entire list of potential IAS. Five hundred and ninety-one species not native to Great Britain were considered. Ninety-three of these species were agreed to constitute at least a medium risk (based on score and consensus) with respect to them arriving, establishing and posing a threat to native biodiversity. The quagga mussel, Dreissena rostriformis bugensis, received maximum scores for risk of arrival, establishment and impact; following discussions the unanimous consensus was to rank it in the top position. A further 29 species were considered to constitute a high risk and were grouped according to their ranked risk. The remaining 63 species were considered as medium risk, and included in an unranked long list. The information collated through this novel extension of the consensus method for horizon scanning provides evidence for underpinning and prioritizing management both for the species and, perhaps more importantly, their pathways of arrival. Although our study focused on Great Britain, we suggest that the methods adopted are applicable globally.

Keywords: biodiversity impacts; consensus approach; freshwater; horizon scanning; invasive alien species; marine; terrestrial.

Figure 1

Horizon-scanning process, based on consensus method (Sutherland et al., 2011), to derive a ranked list of IAS which are likely to arrive, establish and have an impact on native biodiversity in Great Britain over the next decade. The process involved two distinct phases: preliminary consultation between experts within five expert groups (upper arrows) and consensus-building across expert groups (lower triangle).

Figure 2

Possible major direct and indirect effects of quagga mussels on Britain's freshwater ecosystems. Details of interactions are provided in the text. Beneficial effects are indicated with a plus sign, negative effects with a minus sign. Figure adapted and revised from MacIsaac (1996).

Figure 3

Number of species ranked within the top 30 potential IAS within different functional groups (primary producer, herbivore, omnivore, predator and parasite) predicted to arrive into different environments (terrestrial, freshwater and marine) in Britain.

Figure 4

Number of species ranked within the top 30 potential IAS predicted to arrive in Britain into different environments (Terrestrial, Freshwater and Marine) from different geographic regions (Europe, Ponto-Caspian and Baltic Seas, Asia, North America, South America and Africa).

Figure 5

Number of species ranked within the top 30 potential IAS predicted to arrive in Britain by different pathways (defined within Table2) into different environments (Terrestrial, Freshwater and Marine).