Inaction concerning the dispersal of invasive alien species (IAS) via their adherence to anthropogenic vectors remains a global issue for the conservation of aquatic ecosystems (Piria et al. 2017; Ulman et al. 2019; Smith et al. 2020). Although IAS can have detrimental effects on biodiversity and ecosystem functioning across terrestrial and aquatic environments, given their exposure to multiple transport pathways, aquatic ecosystems are considered especially vulnerable to biological invasions and their impacts (Ricciardi and MacIsaac 2011). In addition, unlike terrestrial ecosystems, submerged aquatic environments are particularly difficult to monitor and, consequently, invasions are often well advanced before they become readily apparent (Beric and MacIsaac 2015).

Since 2014, European Union (EU) Regulation no. 1143 has provided the basis for improved spread-prevention, control and eradication of IAS amongst Member States (EU 2014). This legislation commendably targets the transportation, exchanging, keeping and releasing of selected problematic invaders, known as Species of Union Concern. In effect, for these ‘black-listed’ species, trade, deliberate transport, cultivation/breeding, release and ownership is now prohibited within EU territories. In addition, Articles 7(2) and 13 of the Regulation emphasise the requirement for Member States to take all necessary steps to prevent the unintentional introduction or spread of Species of Unions Concern. As of August 2019, this list has grown to encompass 66 IAS, including some thirty aquatic or semi-aquatic species. For the most part, Species of Union Concern designations have focused on species which are traded for commercial purposes (e.g., pet and ornamental), whilst many other damaging non-traded IAS have remained overlooked. In particular, aquatic IAS which inadvertently ‘hitchhike’ on or biofoul anthropogenic vectors, such as fishing and boating equipment, continue to proliferate unchecked amongst EU territories (Ulman et al. 2019). Indeed, prohibition of trade, deliberate transport and ownership will not inhibit sustained dispersal of these insidious invaders, especially small-bodied aquatic invertebrates and plant propagules, which are often difficult to visually detect and readily transportable by accidental means. Accordingly, to better comply with Articles 7(2) and 13 and to address the spread of problematic invaders not currently categorised as of Union Concern, a more proactive approach towards the spread-prevention of IAS is required, and the lack of a unified approach amounts to a missed opportunity for the improved conservation of aquatic ecosystems.

Although awareness campaigns such as ‘Check, Clean, Dry’ promote best-practice biosecurity protocols to curtail IAS, these techniques remain underutilised, underfinanced, and data-deficient (Piria et al. 2017; Smith et al. 2020). Nevertheless, simple decontamination techniques can improve the integrity of aquatic biosecurity protocols (Joyce et al. 2019; Bradbeer et al. 2020). For example, rapid exposure to direct steam and disinfectant treatments have shown promise in biosecurity trials targeting multiple taxonomic groups (see Joyce et al. 2019; Bradbeer et al. 2020, and references therein). However, a current lack of legislation to underpin decontamination undermines the principles of EU Regulation no. 1143, as well as other national and international agreements, such as the United States of America Executive Order 13751 “Safeguarding the Nation from the Impacts of Invasive Species” (EO 2016), and the Ballast Water Management Convention (BWMC 2004). Therefore, in addition to prohibition of IAS, legislative and financial support are urgently needed to enforce and promote management policies with cross-cutting strategic actions, such as unambiguous biosecurity guidelines with multilateral enforcement and the adequate provision of decontamination facilities at major points of waterbody egress (e.g. angling stations, boat ramps and marinas) (Bradbeer et al. 2020; Coughlan et al. 2020).

Enhanced spread-prevention strategies are particularly pertinent given that control or eradication costs following invader establishment can be several orders of magnitude higher compared to spread-preventions, are frequently unsuccessful, and can be damaging to non-target species (see Piria et al. 2017 for discussion). As high-risk IAS do not recognise geopolitical borders, to better improve conservation programmes for aquatic ecosystems, biosecurity protocols designed to target all aquatic IAS should be used to thoroughly decontaminate vectors of adhering organisms. Therefore, regardless of an organism’s black-list designation, ease of visual detectability, known invasion history or likely impact, the risk of further IAS spread can be substantially reduced, if not eliminated, through the adoption of systematic, cheap, readily available and effective decontamination procedures. Nevertheless, further research and increased funding support are still required to develop new, and improve existing, decontamination techniques. In particular, the affordability and application duration times of decontamination treatments remain barriers to user-uptake, especially for larger equipment such as boats, whilst the lack of universally approved guidelines for systematic decontamination continue to inhibit optimal prevention of aquatic IAS.