Biological invasions are increasing in frequency and the need to mitigate or control their effects is a major challenge to natural resource managers. Failure to control invasive species has been attributed to inadequate policies, resources or scientific knowledge. Often, natural resource managers with limited funds are tasked with the development of an invasive species control program without access to key decision-support information such as whether or not an invasive species will cause damage, and what the extent of that damage may be. Once damages are realized, knowing where to allocate resources and target control efforts is not straightforward. Here we present the history of invasive species policy development and management in a large, multi-jurisdictional and multi-use aquatic ecosystem. We present a science-based decision-support tool for on-the-ground aquatic invasive species (AIS) control to support the development of a sustainable control program. Lastly, we provide a set of recommendations for managers desiring to make an AIS control implementation plan based upon our development of novel invasive species research, policy and management in Lake Tahoe (USA). We find that a sustainable invasive species control program is possible when science, coordination and outreach are integrated.

The round goby, Neogobius melanostomus (Pallas, 1814), is one of the most invasive non-indigenous species in the Baltic Sea. It dominates coastal fisheries in some localities and is frequently found in offshore pelagic catches. This paper identifies management issues and suggests actions to be considered for post-invasion management. Priority should be given to the establishment of a coordinated pan-Baltic monitoring programme and associated data storage and exchange, as well as the compilation of landing statistics of the round goby in commercial and recreational fisheries. While eradication is unrealistic, population control that leads to minimising the risk of transfer to yet uncolonised areas in the Baltic Sea and adjacent waterbodies is feasible. This should comprise the requirement that the species be landed in commercial fishery bycatch, the management of ships’ ballast water and sediments, and hull fouling of inland and sea-going vessels, including recreational boats. Extensive involvement of stakeholders is crucial at all phases of the management process.

Invasive alien aquatic species, including marine and freshwater macroinvertebrates, have become increasingly important in terms of both environmental and socio-economic impacts. In order to assess their environmental and economic costs, we applied the Generic Impact Scoring System (GISS) and performed a comparison with other taxa of invaders in Europe. Impacts were scored into six environmental and six socio-economic categories, with each category containing five impact levels. Among 49 aquatic macroinvertebrates, the most impacting species were the Chinese mitten crab, Eriocheir sinensis (Milne-Edwards, 1853) and the zebra mussel, Dreissena polymorpha (Pallas, 1771). The highest impacts found per GISS impact category were, separately; on ecosystems, through predation, as competitors, and on animal production. Eleven species have an impact score > 10 (high impact) and seven reach impact level 5 in at least one impact category (EU blacklist candidates), the maximum score that can be given is 60 impact points. Comparisons were drawn between aquatic macroinvertebrates and vertebrate invaders such as fish, mammals and birds, as well as terrestrial arthropods, revealing invasive freshwater macroinvertebrates to be voracious predators of native prey and damaging to native ecosystems compared with other taxa. GISS can be used to compare these taxa and will aid policy making and targeting of invasive species for management by relevant agencies, or to assist in producing species blacklist candidates.

The Dodecanese region has a high prevalence of marine alien species due to its close proximity to the Suez Canal and associated Suez shipping lanes, as well as its location at biogeographical border between sub-tropical and tropical biota. This region is therefore very important for the early detection of alien species entering the Mediterranean Sea via the Suez Canal and it is imperative that monitoring of alien species is continued in order to assess the levels of biological invasion. We present results of marine alien surveys, carried out in April 2014 on the island of Rodos. Surveys were performed by a team of marine taxonomic experts and students as part of an EU wide training school, coordinated by the COST Action TD1209 “Alien Challenge”. A variety of survey methods were employed to cover a number of coastal habitats. These included: rapid assessment surveys of epibiota on artificial structures in harbours, rapid assessment snorkelling surveys of biota on sublittoral bedrock, and quantified fishing surveys (both boat-seine and trammel net fishing methods). A total of 33 alien and cryptogenic species were recorded across all the survey techniques. Of these species, 9 represented first records for Rodos: the foraminiferan Amphisorus hemprichii, the polychaetes Branchiomma bairdi, Dorvillea similis, Hydroides dirampha and Pseudonereis anomala, the molluscs Aplysia parvula, Chama pacifica and Septifer cumingii, and the bryozoan Hippopodina feegeensis. Of note the record of the Lessepsian invader Dorvillea similis represents the second record in the Mediterranean Sea. Alien fish species represented a small but notable proportion of the diversity, biomass and number of individuals in fishing catch of both fishing methods. All alien fish species observed were already known to be present in Rodos. The addition of species firstly recorded in this study brings the total number of marine alien and cryptogenic species in the Dodecanese region up to 129 species. The vast majority of these alien species have entered unaided via the Suez Canal, but an increasing number have been introduced through hull fouling or ballast water transfer from shipping. The results highlight the value of conducting marine alien surveys with teams of a diverse range of taxonomic expertise, both in its scientific output and student training.

Tubastraea tagusensis and T. coccinea (Scleractinia: Dendrophylliidae) are two corals that have invaded and impacted the southwest Atlantic since the 1980s. Here, we investigated experimentally the use of plastic and raffia sheets, simulating the use of wraps, as an effective method to kill the invasive corals. We showed that by seven days all polyps of the invasive corals were dead in both treatments, probably from lack of oxygen, food and/or due to physical attrition with the wraps. Tubastraea tagusensis was more resistant than T. coccinea, probably due to its different form. The use of plastic sheets was found to be more efficient for killing but raffia was easier to manipulate underwater and allowed an extended period for decomposition of the corals tissues. The use of wraps was demonstrated to be an efficient way of killing and may be added to the management toolbox for the control and eradication of Tubastraea spp. along with fresh water treatment and manual removal.

The giant osteoglossomorph fish Arapaima cf. gigas was introduced to the northern Bolivian Amazon over a half century ago and now contributes significantly to commercial fisheries. Despite this, little is known regarding its current distribution and invasion potential. Here, we address this knowledge gap using two complementary methods: interviewing key informants and examining fisheries landing records in the principal landing site (Riberalta). Both interviews and landing data revealed that the species represents approximately 50% of the total commercial catches, and that it now occupies approximately 340 km² of floodplain lakes in the Beni, Orthon and Madre de Dios River basins. The annual yield is estimated at 258 t, equivalent to 0.76 kg/ha/year. The current geographic distribution represents approximately one-quarter (24%) of floodplain lakes in the lower Bolivian Amazon, suggesting high fisheries potential of the species if it would also colonize the remaining Mamoré and Iténez River basins. The potential for negative ecosystem impacts of the A. cf. gigas invasion seems likely, considering the large body size, life history and feeding ecology of this species, but has not yet been clearly demonstrated. Factors that might limit further expansion are natural barriers (waterfalls) in the lower Mamoré, and periodic cold temperature conditions in the Mamoré and Iténez River basins.

The invasive colonial ascidian Didemnum vexillum (Kott, 2002) was initially discovered in the fall of 2013 near Parrsboro, Nova Scotia. A rapid response survey was conducted in April 2014 to confirm the presence of the species and to determine its distribution near the original detection site. Subsequent surveys between May and August 2014 examined the dredge contents collected during sea scallop stock assessment surveys on German Bank, northern Browns Bank, eastern Georges Bank and in the Bay of Fundy region. The presence of D. vexillum was confirmed at 22 of 30 stations sampled in four areas of the Minas Basin and Minas Channel region in the northern Bay of Fundy during the rapid response survey. The scallop surveys confirmed the presence of D. vexillum at 9 of 829 stations sampled in the Bay of Fundy region, including 7 in the Minas Basin, 1 off Digby Gut and another off the coast of Yarmouth. Due to the presence of a native species, D. albidum, in the region, a PCR assay was developed to distinguish D. vexillum from all other species in the region. Once the PCR assay was validated this assay was used to confirm all positive identifications in this study. Colonies overgrew rocks, bivalve shells and seaweeds or were retrieved as large dislodged fragments. They were in an overwintering state in April, but healthy, and observed to grow into dense mats in summer. In other regions of the world, D. vexillum has been reported to foul shellfish and aquaculture gear, smother benthic organisms such as the sea scallop (Placopecten magellanicus), and overgrow substrates, suggesting this new colonial invasive ascidian poses a potential threat to Eastern Canada aquaculture and commercial benthic fisheries.

Reports of alien crayfish invasions are increasingly common and often associated with well-documented ecological effects including native crayfish biodiversity declines. Because most regions in the U.S. and Canada have not been surveyed to detect the presence and gauge the threat status of such invasions, management agencies lack information on the magnitude of problems in their respective jurisdictions. Our objectives were to catalog, confirm and summarize suspected crayfish invasions that were reported in one U.S. state in recent years. Data were also examined for potential spatial patterns, prevalence of certain species as invaders and effects to native crayfishes. We collected reports of crayfish introductions/invasions from 1998–2014, and attempted to confirm them via sampling. We catalogued 34 reports and confirmed 31 as suspected invasions involving 6 invading species. Procambarus acutus was easily the most frequent invader, and all invading species were native to at least part of Missouri. Most suspected invasions involved species that were legal for commercial sale in the state, but many also involved non-commercial species that are described as “narrow-range endemics.” Invading species were abundant, dominating crayfish communities, at several sites. Native species have apparently declined or been displaced at several locations. Our results suggest the potential for many unreported crayfish invasions in the U.S. and Canada, including those caused by shorter-range (e.g., intrastate) translocations. Ecoregions featuring high crayfish diversity could be threatened with significant declines of native species with narrow ranges. Increased survey efforts in these regions are warranted to estimate threat levels and provide agencies with information to support management actions.

The Fish Invasiveness Screening Kit (FISK) is becoming a popular tool for rapid risk identification of freshwater fishes, with published applications now spanning the globe. Upgrades (i.e., FISK v2) were completed recently to ensure the incorporation of broader climatic zones for its application to the sub-tropical climate of peninsular Florida. The goal of the present study was to evaluate the ability of FISK v2 to identify the potential risk of non-native fishes being invasive in peninsular Florida. The 95 fishes selected for screening were assigned an independent invasiveness ranking using information provided by FishBase and the Invasive Species Specialist Group database. Risk screenings using FISK v2 were then completed separately and independently by five assessors resulting in one to five screenings per taxon. Receiver operating characteristic (ROC) analysis identified a mean threshold value of 10.25 to distinguish between invasive fishes and non-invasive fishes, which, when compared to the independent invasiveness standard, correctly classified 76% of invasive fishes and 88% of non-invasive fishes. This threshold value was considerably lower than many other published calibrations of FISK, emphasizing the importance of regionally focused risk screening. Further supporting these results, 18 (72%) of the high risk species are either established in Florida or have elevated regulatory status by the Florida Fish and Wildlife Conservation Commission. Overall, FISK v2 has proved that it would be a valuable tool for informing management decisions related to the risks of non-native freshwater fishes.

The spread of zebra mussels into new bodies of water is of great concern in the United States due to their economic and ecological costs. Some government agencies suggest the use of vinegar as a decontamination option but do not provide data to explain this decision. This study examined the toxicity of distilled white vinegar on adult zebra mussels at varying concentrations and exposure times. All tested concentrations (25, 50, 75, and 100%) caused complete mortality within four hours. These results indicate that distilled white vinegar can be used for the decontamination of adult zebra mussels.