Ballast water is a leading vector for the introduction of aquatic invasive species worldwide and, once a novel species is established, regional ballast water exchange between ports can accelerate secondary spread. The importance of shipping induced invasions in the Laurentian Great Lakes has resulted in policies that require more stringent ballast water treatment standards for trans-oceanic shipping than is required of ships operating regionally within the Great Lakes. As a result, ballast water discharges within the Great Lakes are not well regulated, primarily because of the challenge of treating the high volumes of water carried by vessels that are confined to the waters of the Great Lakes. We used a discrete-time Markov chain model on a network with annual time-steps to simulate ballast water management scenarios at high-priority ports in the Great Lakes shipping network for two potential invaders, golden mussel (Limnoperna fortunei) and monkey goby (Neogobius fluviatilis). We chose high-priority ports by using graph-theoretic network analysis techniques to calculate six network centrality metrics for 151 ports in the network. Ports scoring high in network centrality scores have more ties with other ports or are positioned within the network such that they potentially have greater influence over the secondary spread of aquatic invasive species than other ports. We simulated secondary spread scenarios where hypothetical ballast water treatment was implemented at the top twenty ranked ports in each network centrality metric, as well as the top twenty busiest ports by ship arrivals. The results of each scenario were compared to a scenario where no management action was taken. Simulated secondary spread for both golden mussel and monkey goby resulted in significantly reduced infestation probabilities (p < 0.001) under all management scenarios when compared to unmanaged spread scenarios. Management at ports with inwardly directed ties to other ports reduced infestations by the greatest amount compared to other management scenarios; 65.4% for golden mussel and 74.6% for monkey goby. The indegree centrality of ports in the Great Lakes was found to be an important factor in governing secondary spread. Here we show that prioritized management, like high volume shore based treatment systems based on network centrality, is a potentially effective strategy for impeding the secondary spread of new or localized invasive species in the Great Lakes.

The European pond turtle Emys orbicularis is seriously threatened across Europe by the non-native common slider, Trachemys scripta, which is included among the 100 most invasive species worldwide. Using ensemble forecast techniques, we analysed the influence of climatic factors on the current distribution of these two species, subsequently projecting the obtained models under two Representative Concentration Pathways (RCPs) to 2050 and 2070, to investigate if global warming would boost direct competition within our study region. We implemented a gap analysis in GIS environment to assess how protected areas (PAs) may be affected by a loss of suitable area for E. orbicularis and by an expansion of T. scripta. An analysis of altitudinal range shift was evaluated, based on obtained projections. We found that both species may gain suitable area in the future, possibly because of the positive effect of increasing temperatures, and are predicted to shift from plain-to-hilly areas towards higher altitudes. These trends result in an increasing overlap of potentially suitable areas for both species, particularly within PAs; moreover, a niche analysis highlights that the results obtained are linked to the environmental niches of the two species. Our findings suggest the necessity, particularly for PAs’ authorities, of field monitoring of T. scripta and further research to more comprehensively assess biotic and abiotic factors influencing the invasiveness of this species.

Dikerogammarus haemobaphes is a freshwater gammarid crustacean native to the Ponto-Caspian region. However, the species is rapidly spreading throughout Western Europe and is classed as a highly invasive species. Here we present a novel eDNA assay aimed at detecting D. haemobaphes and demonstrate its suitability with validation steps conducted in-silico (computer simulations), ex-situ (test of specificity using closely related species) and in-situ (within the field). A survey of freshwater systems in the West-Midlands, United Kingdom, highlighted that D. haemobaphes was present in 26 out of the 39 sites assessed. We conclude that eDNA detection for D. haemobaphes is a promising tool for assessing and mapping the presence/distribution of this invasive amphipod.

Procambarus virginalis, also known as the Marmorkrebs is a highly invasive crayfish species characterized by parthenogenetic reproduction. As conservation management plans rely on the accuracy of the presence and distribution information of invasive species, a reliable method is needed for detecting such species in aquatic systems. We developed and validated a qPCR-based assay for monitoring P. virginalis at low abundance, by detecting their eDNA traces left in freshwater systems. We were able to implement this new assay in-situ at two separate lakes in Germany, where the crayfish were known to be present. Furthermore, we did not detect the pathogenic fungus Aphanomyces astaci in the locations where the Marmorkrebs were detected. We conclude that the use of eDNA is therefore a reliable tool for the early detection of this “perfect invader”.

The Sacramento-San Joaquin Delta is one of the largest estuaries in North America, providing water for more than 700,000 acres of agriculture, recreation and fisheries habitat. For decades, the exotic invasive plant Egeria densa has negatively impacted native habitat and navigation of vessels in the Sacramento-San Joaquin Delta. In 2007 the largest waterbody in the Delta, Franks Tract, began to be managed at operational scale utilizing the aquatic herbicide fluridone. A fluridone pellet formulation was applied to achieve in-water concentrations of fluridone between 2.5 and 3.5 ppb for 8 to 16 weeks in areas with dense Egeria densa. Fluridone applications were started as early as March and continued throughout the treatment period to sustain the target concentrations which were verified by an enzyme-linked immunoassay (ELISA) analytical test. Relative frequency of occurrence for native plants significantly increased from 2006 to 2017 (P < 0.001). Frequency of occurrence of most native species remained variable across years except for Potamogeton richardsonii where frequency of occurrence increased greatly from 3.6% in 2013 to 80% in 2017 (P < 0.001), and significantly increased each year sequentially except between 2015 to 2016 to become the most widespread species. The increase of native plants over the past five years, following management with fluridone, is likely to improve fisheries, native species habitat, and waterway traffic.

Eradication and suppression strategies for established populations of invasive species require innovative but readily available techniques, which maximise efficacy whilst minimising environmental damage. The Asian clam, Corbicula fluminea (Müller, 1774), is a high impact freshwater invader that can dominate macroinvertebrate communities and physically alter benthic habitats. Globally, despite efforts to implement substantial population control measures, C. fluminea continues to invade, spread and persist within freshwater environments. Accordingly, improved eradication, population suppression and rapid reaction techniques are urgently required. As C. fluminea beds can often become exposed during low water conditions, the present study examines the efficacy of an open-flame heat torch, generating ~ 1000 °C, in killing exposed individuals. Direct and indirect applications of the open-flame torch were examined, for C. fluminea residing on top of or within the substrate, respectively. Experiments revealed that ≥ 3 seconds of direct exposure to the flame causes complete mortality of C. fluminea, while only low mortality rates of between 8–11% were achieved for mud-dwelling C. fluminea following 30 seconds of indirect exposure. However, a longer exposure time of 5 minutes can cause complete mortality of buried C. fluminea. Further, combined rake and burn treatments, where the substrate is disturbed between one minute flame applications, can completely kill all C. fluminea specimens residing within beds, following multiple applications. Overall, these results demonstrate that the application of open-flame heat torch treatments can be used for effective, rapid response and substantial population control of C. fluminea populations residing upon naturally and anthropogenically exposed river, lake and canal beds. Although promising, our laboratory results require up-scaling to field application, including examination of other substrate types, increased substrate depth, and greater bed densities of C. fluminea.

A liquid formulation of acid-stabilized ionic copper called EarthTec QZ was used in an effort to eradicate invasive quagga mussels (Dreissena rostriformis bugensis) from an entire 12-hectare lake in Pennsylvania in fall of 2017. The treatment consisted of three separate applications of ionic copper delivered over a period of 37 days with the intent to minimize likelihood of spreading invasive mussels during a one-time water transfer event planned for later that year, from the treated lake to an adjacent river. Mussel mortality was estimated through use of caged adult mussels that were suspended at different locations and depths throughout the lake. Adult mussels began to die within 3 days of the initiation of treatment, particularly in the top 6 meters of the water body. The death of the last caged mussel was confirmed 40 days after the initiation of treatment, in a cage that had been placed in the metalimnion at a depth of 9 meters below the surface. Both biological and physicochemical data collected during the treatment period revealed that there was a pronounced thermocline at 8–11 meters depth. The layer of water in the thermocline resisted mixing, suggesting an explanation for why mussels located above and below this metalimnion were eradicated quickly, yet those within the metalimnion required targeted treatment techniques and 40 days to succumb to 100% mortality. Visual inspection of the shoreline after partial pump-down of the quarry in early November revealed high densities of empty shells from dead adults, and no live adults were found. Analysis of eDNA samples taken in December of 2017 and again in July 2018 concluded no mussel eDNA was detectable. Plankton tows collected and analyzed by microscopy in July, August and September 2018 were rich with zooplankton but no live mussel veligers were found. The cumulative sum of product applied throughout the entire course of treatment totaled 13,500 liters, which is equivalent to 0.44 mg/L as copper as calculated on the full volume of the lake – noteworthy because it is less than half the concentration EPA allows (1.0 mg/L) in a single algaecide treatment. This experience illustrates that low doses of acid-stabilized ionic copper can have profound effects on invasive mussel populations and are a viable management tool. If future sampling confirms that this eradication effort was successful, it will be the first recorded instance of eradicating quagga mussels from an entire lake.

The American bullfrog, Lithobates catesbeianus, has been introduced to all continents with suitable environments and most populations are now viable. This is also the case of the Korean Peninsula, where the invasive L. catesbeianus has a significant negative impact on the local fauna. Here, we review the introduction pathway and population establishment for the species in the Republic of Korea. We then review effective population control methods and make recommendations for the most efficient ways to manage L. catesbeianus populations based on the specific environment of the Republic of Korea. This is the first account of the multiple introductions of the species in the country, the past failures at population establishments, and also the first summary of population control methods that had an impact on population mitigation before their abortion. Our recommendations for population control are based on the local ecology and landscapes and highlight the need for multiple control methods to be used in synergy.

Expansion of non-native fish have caused ecological and economic damage and can negatively impact native fish populations. Current research on deterrent technologies for bighead Hypophthalmichthys nobilis and silver carp H. molitrix have primarily focused on reducing upstream movement in large river lock approaches. However, there is also interest in excluding carp from smaller-scale locations. A water control structure at Emiquon Preserve, Lewistown, Illinois, USA reconnected the Preserve’s wetland lakes to the Illinois River, and is a pinch point that site managers seek to deter immigration of non-native fishes without restricting native fish movement. One possible deterrent strategy that was evaluated within the water control structure in 2017 was the use of a 100 hp boat motor acoustic stimulus. Two underwater speakers were installed in each of two culverts to discourage fish movement though the water control structure. Fish passage was monitored using a series of passive integrated transponder (PIT) antennas in a confined study area. A combination of 176 fish consisting of seven different species (native and non-native) were implanted with PIT tags and relocated downstream of the water control structure. Over 2 days of periodic playback of the acoustic stimulus, 29% of tagged silver carp that were detected crossed though the active underwater speaker array. The acoustic treatment did not significantly reduce silver carp or native centrarchid passage through the culverts. However, numerous silver carp were observed jumping out of the acoustically active culvert at the onset of the stimulus. The acoustic stimulus, especially the frequencies to which silver carp are most sensitive to (< 2000 Hz), rapidly attenuated in the water control structure (water depth 0.55–0.38 m). Depth related attenuation observed in and around the water control structure may have reduced the efficacy of the acoustic fish deterrent system at this location.

Ipomoea batatas (L.) Lam has been recognized as a very competitive crop against certain farming weeds, but more information is required to support its potential field application. The current study utilized a de Wit replacement series incorporating five ratios of I. batatas and Ageratina adenophora (Spreng.) R. M. King and H. Rob plants in 9 m² plots in 2018. In monoculture, the main stem length, leafstalk length, leaf area, and biomass of I. batatas were significantly higher than those of A. adenophora. In mixed culture, the plant height, branch, leaf, and biomass of A. adenophora were significantly suppressed (P < 0.05) by I. batatas. The relative yield (RY) of I. batatas was significantly higher than 1.0, and the RY of A. adenophora was significantly less than 1.0 (P < 0.05) in mixed culture, indicating that the intraspecific competition was higher than interspecific competition for I. batatas, but the intraspecific competition was less than interspecific competition for A. adenophora. The competitive balance index of I. batatas demonstrated a higher competitive ability than A. adenophora. The net photosynthetic rate (Pn) of I. batatas and A. adenophora increased gradually from July to September, and then decreased from September to November in all treatments. The Pn of I. batatas was higher than that of A. adenophora in July and August, less than that of A. adenophora from September to November in monoculture, and the Pn of A. adenophora was significantly suppressed (P < 0.05) with increasing proportions of I. batatas in mixed culture after August. The activities of antioxidant enzymes superoxide dismutase, peroxidase and catalase for A. adenophora were significantly reduced (P < 0.05) with increasing proportions of I. batatas in mixed culture. Our results showed that plant growth of A. adenophora was significantly suppressed by I. batatas competition due to certain morphological and physiological advantages of I. batatas. Therefore, I. batatas is a promising replacement control candidate for managing the infestations of A. adenophora, reducing the soil seed bank and seedlings of A. adenophora.

The eradication or control of invasive small Indian mongooses from islands likely requires toxic baiting when removal by trapping proves insufficient. The one toxic bait currently registered for mongooses in the United States has relatively low palatability and efficacy for mongooses. Developing and registering a new pesticide can be very expensive, while funding for developing toxicants for mongooses is limited. Once registered, use of a toxic bait may be hindered by other factors, such as public opposition to an inhumane toxicant, poorer efficacy than expected, or if the toxic bait is difficult for applicators to apply or store. Therefore, we conducted a product feasibility assessment comparing the registration and use potential of toxic baits for mongooses containing either bromethalin, diphacinone, para-aminopropiophenone (PAPP), or sodium nitrite (SN). We estimated that a diphacinone bait would be the cheapest and fastest to register, and more application methods may be allowed compared to the others. On the negative side, we ranked diphacinone as the least humane toxicant of the four, largely due to a prolonged time to death following exposure and onset of symptoms. However, this interval also increases the probability that the antidote can be administered following an accidental exposure. If an alternative toxicant is required, use of a bromethalin, PAPP, or SN bait would likely be limited to bait stations or burrow baiting due to primary risks to non-target species. A bromethalin bait would be the cheapest and fastest to register of the three, particularly if a bait that is already commercially available proved efficacious for mongoose. However, we ranked bromethalin lower than PAPP or SN for overall humaneness. A PAPP bait would be slow and the most expensive to register. An SN bait would be challenging to formulate into a palatable bait with a reasonable shelf life. Although we focused on the U.S., mongooses are invasive in many parts of the world and the regulatory and use requirements for pesticides in other countries are generally comparable. In addition, our feasibility assessment can serve as a template or starting point for managers considering development of toxicant products for vertebrate pests.