Management of invasive species, whether prevention, population reduction, or eradication, requires assessment of the invasive species’ population status and an assessment of the probability of success of management options. Perceptions of a species’ permanence in an environment or lack thereof frequently drives how limited time, financial, and personnel resources are allocated to such efforts. Language we use to describe a non-native species’ status largely defines these perceptions and sets boundaries, real or perceived, to potential management actions. Here we discuss the use of a particular term – “established” – when confronting management decisions for invasive species. Our objective is to contribute to bridging the gap between the realms of conceptual development and management with respect to use of the term “established”. We find that although there are benefits of polysemy and synonymy to conceptual development they present an additional challenge to managers who must weigh the costs, benefits, and potential for success of particular management actions. We also examine how existing conceptual frameworks might be augmented to bridge the theoretical-practical gap, such as more precisely defining potential management actions and explicitly including assessment of risk.

The advent of container vessel networks has revolutionized global freight transport. While numerous studies in various disciplines such as economics, law, geography, engineering, and more, have discussed the impact of the “Container Revolution”, we would like to share our insights here regarding the impact of container shipping networks on current and potential future trends in marine bioinvasion. We discuss the shift in centers and routes of high shipping intensity, and the importance of “Hub” versus “Feeder” ports, in relation to potential invasion routes. The increasing use of Ultra-Large Container Vessels (ULCV) worldwide is leading to further change in introduction dynamics: fewer vessels are now required for the transshipment of goods, as evident from our analysis of vessel movement via the Suez Canal.
An investigation of adapted maintenance regulations is thus required in order to prevent the spread of alien species as fouling communities on particular niche areas of ULCVs. ULCVs further advance the hub-and-spoke network. Hub ports are characterized by the close physical proximity of large vessels (intercontinental mainliners) to many smaller vessels (feeders), calling in at local ports, as well as to other large vessels. This vessel interface occurs on a regular repetitive weekly cycle within a relatively small maritime environment. Thus a systematic network of potential vectors of bio-invasion is being established on both regional and continental levels. The increasing development of large container ports globally, and of larger vessels, demands a thorough investigation of their effect on bioinvasion potential. An integrated study of both the commercial and the biological networks is thus essential in order to fully comprehend their interaction.

International and national guidelines and regulations to limit the inadvertent transfer of non-native species on the submerged surfaces of vessels and mobile infrastructure are progressing. However, methods to assess compliance must be developed to assist both regulators and industry. While there is a history of biofouling inspections in maritime industries, including commercial shipping and infrastructure, such surveys are tailored for vessel safety and performance rather than being driven by biosecurity purposes. Thus, these inspections are likely inadequate for confirming compliance with biosecurity regulations. To determine regulatory compliance, agencies will likely rely on a combination of risk profiling, assessment of documentation of biofouling management, archival data and images, and real-time in-water surveys made by divers or remotely operated vehicles (ROVs) specific to biosecurity regulations. Divers may exceed ROVs at finding organisms in recesses and other topographically complex areas, and when regulations require confirmation of species identity or viability. In contrast, ROVs may be well suited for regulations that establish upper thresholds on biofouling levels with little concern for organism identity or condition. Several factors will inform how a survey is conducted, including cost, the type of data required by regulations, environmental conditions, safety, and logistics. Survey designs and requirements should be transparent to manage industry’s expectations of border procedures, to increase the efficiency with which industry and agencies manage biofouling and potentially align the evaluation of best practices in hull and niche area maintenance across jurisdictions.

This work presents a current (2018) annotated list of marine NIS and cryptogenic species in Greek marine waters. For this purpose, we updated information from previous lists, included new data from several new NIS and cryptogenic records and recent taxonomic studies, and followed current taxonomic modifications for the alien/cryptogenic status of several introduced species. Our extensive literature survey and revisions resulted in the exclusion of 61 species, which were included in previous lists, and the addition of 41 new alien species reported in the 2016–2018 period plus ten old NIS records. The current number of introduced species in Greek waters whose presence is not questionable includes 214 alien species and 62 cryptogenic species. Approximately 80% of the introduced species in Greek Seas consists of the taxa—in decreasing order—Mollusca, Polychaeta, Crustacea, Fishes, and Macroalgae. Nevertheless, a considerable increase in the number of NIS Bryozoa and Ascidiacea was observed within the last decade. Unaided natural dispersal of Lessepsian immigrants (57%) and transport-stowaways (36.7%) are the major pathways of introduction reported for Greek waters. However, with few exceptions (6.8% of species), the confidence level in assigning a pathway was medium to low. Several species reported from adjacent marine areas are expected to reach Greek waters within the next years. The intensification of underwater observations by citizen scientists combined with further research in hot spot areas, understudied habitats and overlooked taxa will significantly raise the number of NIS species in Greek waters. This study can serve as a basis that could greatly benefit from the coordination and harmonization of monitoring initiatives under international, EU and Regional Policies, and the compilation of new data from established monitoring programs, and rapid assessment surveys.

Invasive marine species (IMS) are thought to be one of the most serious anthropogenic threats to global marine biodiversity. There are numerous reports of IMS being introduced into new areas throughout the world, but relatively few are in tropical locations. It has been suggested that this is an artefact of our lack of knowledge species present in the megadiverse tropics and a lack of IMS surveys. The Pilbara in northern Western Australia (WA) is used as a case study to examine these questions. The area is at high risk of IMS because of extensive international shipping. A detailed literature search of marine biodiversity studies developed a database of 5,532 species recorded in the Pilbara. There have been numerous surveys for species on the Australian national and WA IMS lists but only one, the ascidian Didemnum perlucidum Monniot, 1983, has been found.

The composition of biofouling communities on colonised terracotta tiles was assessed in mariculture areas of the northern Adriatic Sea (Croatia) according to a hierarchical nested sampling design. Significant differences in the composition of biofouling assemblages were detected between depths (1 and 5 m) and at the larger spatial scale (tens of km). Additionally, the biofouling community showed different patterns in relation to the time of immersion (2, 4, 6 and 8 months). The most abundant taxa were Spirobranchus triqueter, Spirorbis spirorbis, Ostrea edulis, Mytilus galloprovincialis, Schizoporella sp., Balanus sp. and Botryllus sp. The invasive Anadara transversa was consistently an important component of these biofouling assemblages. It was able to spawn throughout the duration of a survey (April to January) showing peak recruitment during the summer. A maximum density, up to 500 individuals m^-2, were assessed at the depth of 5 m. Maximum shell length of 30 mm was recorded at the end of the experiment. These results suggest that, besides the native fouling community species, the invasive and opportunistic A. transversa might cause additional problems in mariculture facilities of the northern Adriatic Sea.

Environmental DNA (eDNA) has improved detection probabilities of aquatic invasive species but lab-based analytical platforms for eDNA analyses slow opportunities for rapid response. Effective approaches that address this analytical bottleneck and improve capacity for rapid response are urgently needed. We tested the sensitivity of a portable, field-based eDNA platform relative to widely used lab-based eDNA approaches for detecting invasive northern pike (Esox lucius) in eight lakes on Alaska’s Kenai Peninsula. The portable, field-based platform takes ~ 1 hr from sample collection to final results and uses a field-based DNA extraction kit, a shelf-stable assay, and a portable real-time PCR thermocycler. Lab-based approaches take days to weeks to months for final results and use lab-based DNA extraction kits, lab-bound assays, and benchtop real-time thermocyclers. We found that the portable, field-based approach was less sensitive than lab-based approaches and was more prone to inhibition, thus increasing potential for false-negatives. Until sensitivity and inhibition issues can be resolved, this portable, field-based approach is best viewed as a complement to rather than a replacement of standard eDNA lab-based approaches.

Aquatic alien invasive species (AIS) are a substantial and increasing threat to biodiversity and ecosystem function worldwide. In particular, invasive aquatic macrophytes, such as the South African curly waterweed Lagarosiphon major ((Ridley) Moss 1928), induce major environmental change that often culminates in wide-ranging ecological and socio-economic impacts. Currently, there is a lack of effective biosecurity protocols to mitigate against such invader spread. Here, we examine the efficacy of a broad-spectrum aquatic disinfectant, Virasure® Aquatic, to induce mortality of L. major propagule stages. We assessed the efficacy of Virasure® Aquatic at contact times of 1, 2 and 5 minutes, using 1% (10g L^-1) and 4% (40g L^-1) concentrations. A necrosis scale was applied to visually assess tissue degradation. Necrosis increased with longer chemical contact times, with fragment degradation optimised at 2 minutes at 1% concentration and 1 minute at 4% concentration. Mode of application was also critical to treatment effectiveness, with spray treatments less effective than submersion treatments. We recommend the use of Virasure® Aquatic via submersion for a minimum period of 2 minutes at 1% concentration or higher. While spray applications should be applied when submersion is not feasible, such as with large water craft, increased spray times beyond those assessed here should be examined. However, results presented suggest that Virasure® Aquatic can effectively reduce the secondary spread of invasive L. major, and may thus form an integral part of biosecurity protocols. The use of broad-spectrum disinfectants and other readily available treatments, that were not purposefully developed for aquatic AIS control but nevertheless are emerging as effective in aquatic AIS management, is discussed and encouraged.

Lake Caicedo Yuso-Arreo (Spain) supports dense populations of alien fish species, namely common carp (Cyprinus carpio), largemouth bass (Micropterus salmoides), pumpkinseed (Lepomis gibbosus), and the red swamp crayfish (Procambarus clarkii). These introductions have caused a reduced transparency, decreasing submerged vegetation and population decline of native tench (Tinca tinca). Alien species were caught and removed for 76 days in 2014 and 2015 with the objectives of eradicating carp and reducing largemouth bass and pumpkinseed populations under 20% of 2014 observed density and biomass. Only two individuals of tench were captured, underlining its scarcity. A total of 27,077 individuals (1089 kg) of alien species were removed, but eradication was not achieved for any species. The largest sizes of carp and largemouth bass almost disappeared, while in 2015 an increase in the abundance of large recruits was observed. A hydroacoustic fish stock assessment was carried out at the end of the action in 2015 to obtain data on fish density and biomass in open water as a mean to compare results to measurements from 2010. Although the density of fish increased from 2010 to 2015, biomass fell drastically. In 2017, the alien species community was controlled again, revealing a substantial recovery from previous control efforts, a change in the size distribution towards smaller specimens and interactions among North American species. Additionally, no tench could be identified and the species is considered locally extinct. Thus, the results from this study suggest the need for ongoing control efforts with increased electrofishing and implementation of alternative control methods such as the introduction of biological control agents to achieve the ecological status improvement and environmental restoration goals.

Concern about electrofishing inadvertently harming the embryos of species of conservation concern has motivated much of the research that describes what electrical conditions can kill fish embryos. As a result, targeted electrofishing might be underutilized as a potential control method to reduce the recruitment of nuisance fishes like common carp (Cyprinus carpio), one of the most widely distributed invasive fish in North America. We evaluate the efficacy of using electricity to reduce common carp recruitment by examining embryonic survival while manipulating the transfer of electric power to developing carp embryos. Embryos were shocked in water from a carp-occupied area (ambient conductivity 127 µS/cm) using a variety of voltage gradient and waveform treatments common to commercial electrofishing units and generators. Survival of electroshocked common carp embryos was ≤ 50% at power densities (12,700 µW/cm³) and voltage gradients (10 V/cm) that failed to cause significant mortality in other cyprinid species; however, embryonic resistance to electroshock was first noted at almost 3 d after fertilization (survival ≤ 50% at 79,375 µW/cm³). Power transfer theory was used to explore optimal water conductivities for the deployment of electrical control of fish embryos at shallow endorheic lakes by using conditions at Malheur Lake as an example. Power transfer theory suggests that at relatively high water conductivities it becomes more difficult to achieve power transfer thresholds sufficient to kill small fish embryos without exceeding the power capabilities of commercially-available electrofishing equipment, and that power transfer to the embryo drops below 50% of the total power applied when water conductivities exceed 325 µS/cm. Thus, water chemistry conditions most amenable to killing carp embryos with electricity in an arid, endorheic lake like Malheur Lake would most likely occur at lake inflows or more generally when the lake level is elevated. However, when spawning is dispersed or more spawning habitat is available during higher lake levels, the resulting increase in areas that require treatment may present logistical challenges. Managers considering the use of electrofishing to control recruitment of an invasive fish like common carp should consider the spatio-temporal arrangement of spawning sites, the spatial scale of the necessary control treatment, how compensatory effects may influence the overall population response, and the need for concurrent control methods targeting other life stages.

Common carp (Cyprinus carpio Linnaeus, 1758), one of the world’s most invasive fish, is known for their extensive seasonal migrations. Often, adult carp migrate between lakes and marshes (spawning grounds) in early spring in large synchronized events. If these fish could be directed into traps, sustainable carp management schemes could be developed for many lake-marsh systems. In this study, we used a portable low-voltage electric guidance system (EGS) to direct common carp into a mock trap in a relatively large natural stream. The system was tested on 6 occasions: 3 days with EGS off and 3 days with EGS on. Approximately 40 adult carp were used in each test. All were implanted with passive integrated transponders (PIT) and ten in each group also had visual markers. When the EGS was on, PIT data indicated that 74% of the carp were successfully guided into the mock trap, while visual markers indicated that no carp were able to cross through the EGS despite over 300 attempts. When the EGS was off, PIT data indicated that only 18% of carp swam into the mock trap, and visual markers showed that many were able to swim though the EGS (22 out of 29). The electric field generated by the EGS was mild and did not cause fish paralysis. The EGS required little on-site engineering and was deployed in 2 days. This new type of EGS might prove useful for managing invasive fish or for conservation of native species that employ seasonal migrations.

Construction of a water management structure (WMS) in the levee surrounding The Nature Conservancy’s Emiquon Preserve (Havana, Illinois, USA) created a new hydrological connection and potential aquatic invasive species pathway between the Illinois River and a large conservation wetland complex. Site managers need a control tool that deters the upstream passage of non-native fishes into the wetland lakes, but does not interfere with normal gate operation and water discharge. This short field study evaluated carbon dioxide (CO₂) injected into water as a non-obstructive method to reduce fish abundance near the WMS culverts. We quantified relative fish abundance using underwater sonar with and without injection of CO₂ into culverts during three discharge events: no flow (0 m³/s), restricted flow (0.9 m³/s), and unrestricted flow (3.2 m³/s). Overall, CO₂ reached or exceeded our target concentration of 100 mg/L during no flow and restricted flow, and fish abundance was 70–95% lower at culvert entrances relative to untreated control days. The target CO₂ level was not reached during unrestricted flow and fish abundance was not reduced during CO₂ injection. Atmospheric CO₂ concentrations were inconsequential and unaffected by CO₂ treatments throughout testing. Results from this initial field study provide several considerations for CO₂ as a fish deterrent in natural environments.

Hazard characterization and risk assessment are commonly used to prioritize vectors of nonindigenous species (NIS) for inspection or other prevention opportunities. Commercial shipping vessels are a target of such vector-based management since ballast water has been known to transport NIS between aquatic ecosystems globally. Here we used a risk-based screening protocol to prioritize vessels discharging ballast water to the lower Columbia River and Oregon coast. We began by adapting established methods of assessing risk factors that influence the initial stages of the invasion process (arrival and survival). We created relative risk scales for each factor using data collected from vessels that discharged ballast water in three unique zones within our study area. We then organized a decision tree based on the confidence level of the proxies used for each risk factor to create a tool that prioritizes vessels with high risk ballast water for attention from regulatory personnel. In order of consideration, decision tree factors included: intent to discharge ballast water, reported adherence to required management practices, environmental distance between source and discharge locations (habitat suitability), ballast water discharge volume (propagule pressure number and frequency), and ballast water age (organism viability). As a result, vessels were prioritized on a scale of low, medium, medium-high, or high. We applied the decision tree to a 2016 dataset of vessel arrivals and found that 173 of 1,592 arrivals were deemed high priority, with most occurring at ports in the freshwater zone of the Columbia River (158), followed by fewer in the estuarine zone of the Columbia River (4) and in Coos Bay (11). The decision tree is transferable to NIS prevention and regulatory efforts in other port systems. The vessel prioritizations are adaptable for managers using risk assessment strategies to allocate limited regulatory program resources for vector screening.

Mariculture of Cobia (Rachycentron canadum) has become popular in various regions of the world due to the species’ hardiness, fast growth and high market value. Despite not being native to the Eastern Pacific, Cobia was introduced for offshore sea-cage aquaculture in Ecuador in 2015, with the first Cobia escape occurring there several months after that culture effort began. Here, we report on new sightings of mature Cobia in the Colombian Pacific coast in 2017 with evidence that this alien fish is able to integrate into food webs and reproduce in the region. Using a decision-support tool developed for aquatic species (Aquatic Species Invasiveness Screening Kit, AS-ISK), we screened Cobia to identify its potential of becoming invasive in the tropical eastern Pacific (TEP). Based on the present state of knowledge, AS-ISK results indicated that Cobia has a medium to high risk of becoming invasive in this region. These results indicate that Cobia sea-cage mariculture in the TEP is not advisable. Carangid fishes native to the TEP that are already used in sea-cage aquaculture elsewhere provide an alternative to Cobia mariculture.

Determining which species should or should not be on priority lists of invasive alien species is far from trivial. It is rare to have sufficient data to obtain empirical estimates of whether an individual species should be included or excluded and so risk assessment protocols depend heavily on expert-opinion. A challenge is deciding what to do if experts have different opinions. Few published studies have attempted to quantify the diversity of opinion among experts and in most circumstances final lists are presented as if they were the outcome of full consensus. Here we used an iterative expert elicitation process and combined this with statistical modelling to develop a list of “High Threat” alien plant species in the context of ecological restoration. Competition from invasive alien plant species can be a major cause of restoration failure, but not all alien species pose a threat to restoration success. The development of a list of persistent and invasive alien species that competitively exclude native plant species and reduce the probabilities of successful ecological restoration could improve our ability to distinguish between those sites where ecological restoration is more likely to succeed and those sites where it could be a costly failure. Nine experts assessed 263 alien plant species over multiple assessment rounds. Full consensus among experts was achieved for only 20% of species but the iterative process reduced the number of uncertain allocations. Alien plant prioritisations rarely communicate the range of expert-opinion and here we demonstrate; (i) that opposing opinions can be prevalent, (ii) that capturing this variability is important, and (iii) how to accommodate it analytically. Using a precautionary and transparent approach, we generate a list of 201 alien species thought likely to reduce ecological restoration outcomes. This list synthesises current expert opinion and knowledge and will be used to guide conservation and restoration actions in in New South Wales, Australia.

The amphibious invasive alien Crassula helmsii is native to Australasia and introduced in Europe. This species negatively affects wetland ecosystems by outcompeting native species, impeding water flow, reducing dissolved oxygen and stimulating redox processes. Therefore, effective eradication measures are required. However, a comprehensive overview of available eradication measures for C. helmsii and an assessment of their effectiveness are lacking. The effectiveness of eradication measures for C. helmsii was systematically reviewed. A literature search included scientific journal papers and reports to compile a consistent data set on effectiveness of 59 eradication studies in short-term and long-term. Only measures aiming at complete eradication of the species were assessed and classified (i.e., chemical, mechanical, physical and combined treatments). Effectiveness of these measures was low. Only 10% of the studies reported an effective eradication of the species. Separate and combined eradication measures appeared to be potentially effective immediately after treatment in 32% and 45% of the studies, respectively. However, these measures were only effective in the long-term in 8% and 14% of the studies, respectively. Effectiveness of measures was often insufficiently documented or/and monitored. For instance, information on treated surface area and scale, effects on non-target species and costs of the eradication program was mostly lacking. Eradication measures failed because of species plasticity and adaptation to a wide range of ecosystems. Furthermore, there was a lack of preventive measures against recolonization. Conditions for successful eradication are small-sized area of infestation, presence of the species in a (hydrologically) isolated system and terrestrial growth. Eradication is unlikely if these conditions are not met. Prevention, population control and containment of the species appear to be the only achievable management options in such cases.

A large portion of East African ecosystems are officially protected, yet increasing wildlife tourism and infrastructural development are exposing these areas to invasion by alien plant species. To date there has been little quantification of alien plant species in the Serengeti National Park, Tanzania. In this study, we aimed to: (1) establish a list of common alien plant species; (2) quantify the frequencies of alien species near roads and settlements (i.e. tourist lodges and a campsite), and (3) estimate the abundance (plant cover) of alien plant species in relation to source activities (i.e. gardening) and park management (i.e. fire). In total, we detected 15 alien plant species in our surveys with an 80% probability of encountering an alien species within the first 50 m from a road or settlement. Overall, we found no difference in the presence of alien species near roads or settlements, but did find a significant decline in species presence with distance from these sources. Cumulative fire frequency was the most important factor influencing the abundance of alien species with the highest alien plant cover in areas with infrequent or no fires over the last 13 years. There was no difference in alien plant cover in relation to other commonly cited source activities, which may be due to the stronger influence of fire. Although the abundance of the majority of alien plant species was negatively related to fire, some species, notably Tagetes minuta, had higher cover with more frequent fires. Our results contradict findings from other African savannahs that suggest fire promotes invasive species and this is likely due to the species-specific interactions with fire. In the Serengeti, fire will be difficult to use as a management tool due to variable species response. Thus, we highlight that other management approaches such as physical removal and biological control agents can be implemented; however future work with these techniques should also consider the interaction of alien plant species with fire.

Summarizing historical records of potentially invasive species increases understanding of propagule pressure, spatiotemporal trends, and establishment risk of these species. We compiled records of non-native pythons and boas from the Florida Keys, cross-referenced them to eliminate duplicates, and categorized each record’s credibility. We report on 159 observations of six python and boa species in the Florida Keys over the past 17 years. Burmese pythons (Python bivittatus), boa constrictors (Boa constrictor), and ball pythons (Python regius) are the most frequently reported species, but credible records of three additional species were also reported. Among the most notable records, we report on three hatchling and multiple reproductive Burmese pythons captured on North Key Largo since 2016, indicating that the species is now established on that island. The expanding mainland Burmese python population and ongoing python and boa introductions via pet and cargo pathways are likely to keep propagule pressure high in coming years. Both effective public outreach to solicit reporting of sightings and effective early detection and rapid response networks may help to prevent further establishment and associated ecological impacts of python and boa species in the Florida Keys.