Harbours are known introduction foci of marine alien species. They act as recipients of new introductions and as sources for regional spread. We report on subtidal surveys of fouling communities from 14 harbours along the coastline of South Africa that were used to identify predictors of high alien species numbers in support of prioritisation of monitoring actions by authorities. The harbours varied in nature from large, international shipping hubs to small, regional fishing harbours and recreational marinas. Fouling assemblages were assessed using visual and scrape sampling to ensure the detection of large, mobile and small inconspicuous species. In total, 29 alien species were recorded, 15 of which were detected outside of their previously known ranges. The number of species recorded per harbour varied from five to. Results revealed that high numbers of alien species were associated with the presence of yachts and low primary productivity. Harbours which had yachts and occurred in areas with mean Chl a minimum levels lower than 0.21 mg.m^-3 had the highest number of alien species, while harbours without yachts that were larger than 0.1km² supported the fewest alien species. These findings suggest that the presence of yachts can be used to identify harbours with high numbers of alien species, particularly in regions with low productivity. While the applicability of these findings to other regions remains to be tested, this work suggests that harbours that fall within this category could be prioritised for monitoring of marine alien species.

The introduction of aquatic invasive species to non-native habitats can cause negative ecological effects and also billions of dollars in economic damage to governments and private industries. Once aquatic invasive species are introduced, eradication may be difficult without adversely affecting native species and habitats, urging resource managers to find preventative methods to protect non-invaded areas. The use of ozone (O₃) as a non-physical barrier has shown promise as it is lethal to a wide range of aquatic taxa, requires a short contact time, and is relatively environmentally safe in aquatic systems when compared to other chemicals. However, before O₃ can be considered as an approach to prevent the spread of aquatic invasive species, its effects on non-target organisms and already established aquatic invasive species must be fully evaluated. A review of the current literature was conducted to summarize data regarding the effects of O₃ on aquatic taxa including fish, macroinvertebrates, zooplankton, phytoplankton, microbes, and pathogens. In addition, we assessed the practicality of ozone applications to control the movement of aquatic invasive species, and identified data gaps concerning the use of O₃ as a non-physical barrier in field applications.

A thorough assessment of aquatic nonindigenous species’ risk facilitates successful monitoring and prevention activities. However, species- and vector-specific information is often limited and difficult to synthesize across a single risk framework. To address this need, we developed an assessment framework capable of estimating the potential for introduction, establishment, and impact by aquatic nonindigenous species from diverse spatial origins and taxonomic classification, in novel environments. Our model builds on previous approaches, while taking on a new perspective for evaluation across species, vectors and stages to overcome the limitations imposed by single species and single vector assessments. We applied this globally-relevant framework to the Laurentian Great Lakes to determine its ability to evaluate risk across multiple taxa and vectors. This case study included 67 aquatic species, identified as “watchlist species” in NOAA’s Great Lakes Aquatic Nonindigenous Species Information System (GLANSIS). Vectors included shipping, hitchhiking/fouling, unauthorized intentional release, escape from recreational or commercial culture, and natural dispersal. We identified potential invaders from every continent but Africa and Antarctica. Of the 67 species, more than a fifth (21%) had a high potential for introduction and greater than 60% had a moderate potential for introduction. Shipping (72%) was the most common potential vector of introduction, followed by unauthorized intentional release (25%), hitchhiking/fouling (21%), dispersal (19%), stocking/planting/escape from recreational culture (13%), and escape from commercial culture. The ability to assess a variety of aquatic nonindigenous species from an array of potential vectors using a consistent methodology is essential for comparing likelihoods of introduction, establishment, and impact. The straightforward design of this framework will allow its application and modification according to policy priorities by natural resource managers. The ability to use a variety of information sources facilitates completion of assessments despite the paucity of data that often plagues aquatic nonindigenous species management.

Invasive alien species (IAS) are considered an important threat to global biodiversity due to major ecological impacts. In 2014, the European Union (EU) introduced a regulation (EU) No 1143/2014 on the prevention and management of the introduction and spread of IAS. The first risk prioritized list of IAS of EU concern was adopted on the 3rd of August 2016. EU member states are required within 18 months to carry out a comprehensive analysis and prioritisation of the pathways of unintentional introduction and spread of these IAS in their territory. Horizon-scanning is a method of IAS prioritisation through the systematic analysis of potential future IAS and identification of new opportunities for IAS management. However, horizon-scanning has mostly been applied on a national basis only, leading to a fragmented approach within the EU and ignoring the potential for IAS to cross international borders. We present a novel framework for horizon-scanning applicable at a continental scale. Our method maximises the use of available data from climatically matched countries by applying a harmonisation and aggregation method, and elucidates the relationship between pathways, impact types and species groups for risk prioritised IAS. Application of the method produced a list of potential IAS for the Netherlands revealing that the international trade in plants and animals is the most important pathway for the introduction of IAS. The horizon-scanning provided a starting point for the design of preventative, early identification and rapid action measures for the effective management of potential IAS.

The status of the Asian kelp Undaria pinnatifida, was determined using the abundance and distribution range method during a rapid assessment survey. This kelp was first found on the northeast coast of Ireland at Carrickfergus Marina in Belfast Lough, Northern Ireland in 2012. It was not known in Ireland in 2006. U. pinnatifida was one of a set of target species searched for during 2012, and initially it occurred at low levels. By 2013 its population had expanded within this marina. In 2014, some tens of individuals were found for the first time over a hundred kilometres to the south in the Republic of Ireland at Carlingford Lough. Both senescent and young plants were found at these sites. In 2015, the kelp appeared at Glenarm Marina 40 km to the north of Carrickfergus; and in the following year, the population had increased marginally. The kelp was not found at a marina on the south side of Belfast Lough, most probably due to fluctuations of salinity. This account discusses the value of the ADR method for evaluating the recent arrival of this large and easily recognised species .

With a voracious appetite for juvenile fish and invertebrates, invasive alien red lionfish (Pterois volitans) constitute one of the greatest threats to the Caribbean’s coral reefs. Although the eradication of lionfish is no longer considered possible, population suppression to site-specific densities can allow native fish populations to recover. Understanding the diet of lionfish in invaded areas is critical to understanding local impacts they pose to coral reef communities. This study explored the diet of lionfish in the northern end of the Belize Barrier Reef and tested whether biological variables (size, sex or reproductive stage) affect the diversity and/or abundance of prey species consumed. Between 2011 and 2014, 1023 lionfish were dissected and their gut contents analysed in the Bacalar Chico Marine Reserve. Gut contents analyses revealed that large sized lionfish consumed the highest abundance of prey (Mean (M)= 3.27 prey items) compared to small (M= 1.74 prey items) and medium (M= 3.15 prey items) lionfish, and that reproductive females consumed a higher abundance of prey (M= 3.66) compared to non-reproductive females of the same size (M = 2.85). As we found that medium and large lionfish are generalist predators and feed on a diverse assemblage of prey items, the effects of lionfish on the biomass of any one species may be reduced. This may enable individual prey species to have relatively stable abundances, although this hypothesis bears further testing. If management efforts are focused on improving a site-specific population of an individual prey species, such as an endemic or threatened fish, it is important to include removal efforts of small lionfish, particularly if they inhabit the same niche habitat. However, we recommend that existing lionfish focused cull dives continue using non-size discriminatory methods in order to account for site-specific, ecologically and commercially important prey items and to deter the likelihood of a successful invasion.

Overland transport of recreational boats is among the most important distribution vectors for aquatic invasive zebra and quagga mussels between inland waters. Simple measures such as instructing boat owners how to prepare their boat for transport so that the boat does not carry invasive species are considered to be important prevention measures. Nevertheless, the net effects of such measures are poorly understood and the boat cleaning behavior of boat owners has never been studied in detail before the implementation of such preventive measures. Using a “self-report” questionnaire, we investigated the boat cleaning behavior of boat owners in Switzerland where almost no preventive measures have been taken yet. We found that the self-reported boat cleaning rates are high, with 92% of boaters cleaning their boat upon finding mussels attached to their boat and 84% of them cleaning their boat before a transport. Nevertheless, only half of the boat owners report using high pressure washing to clean their boat before overland transport and many use ineffective cleaning methods. We show the importance of informing boat owners on the appropriate methods to remove invasive species from their boat and suggest that high pressure washing facilities should be made available at all potentially infested water bodies. Furthermore, our analysis shows that the boat cleaning behavior could be significantly improved by changing how boat owners value the perceived costs and benefits of cleaning, as well as by increasing their awareness of the potential negative impacts on aquatic ecosystems caused by non-native species. With regard to a possible spread of zebra mussels to uninfested alpine lakes and the imminent spread of quagga mussels in Switzerland, we conclude that the Swiss boating community would be open to accepting implementation of prevention measures.

The Asian green mussel Perna viridis is an abundant and important ecological and economical species across its native range. However, outside its native range, this species has been considered invasive and concerns have been raised worldwide regarding its potential impacts. Despite this, little work has been done to investigate the genetics of native and/or introduced populations of this species. In the present study, we developed 16 new polymorphic microsatellite markers using the Illumina MiSeq Platform. Four to 15 alleles per locus were detected. There was no evidence of linkage disequilibrium between pairs of loci and all loci were in Hardy-Weinberg equilibrium.

The potential of environmental DNA (eDNA) methods to enhance the detection of invasive species during routine monitoring is of interest to management agencies. Here we applied the eDNA methodology concurrent with conventional detection techniques during two routine monitoring seasons to detect the presence of three invasive fish in Australia with contrasting spatial distributions (benthopelagic, pelagic and benthic): common carp (Cyprinus carpio), redfin perch (Perca fluviatilis) and Oriental weatherloach (Misgurnus anguillicaudatus). Our objectives were to compare the seasonal detection of the target species using eDNA and conventional detection (fyke nets), determine the relationship between catch per unit effort (CPUE) and DNA copy number and ascertain the best water location (surface vs. subsurface) for eDNA detection. Our results show that eDNA had a higher detection rate than fyke nets for Oriental weatherloach and redfin perch during both the autumn and spring surveys. Common carp was detected at all sites for both seasons using fyke nets and eDNA with the exception of one site during the autumn survey where common carp was captured using fyke nets but no carp eDNA was detected. Season had a significant effect on DNA concentration for common carp (P<.005) and Oriental weatherloach (P=.002) but sampling location (surface vs. subsurface) had no significant effect on DNA concentration for all three species. We found a positive correlation between CPUE and DNA copy number for Oriental weatherloach (rs = .718, α = .045) and redfin perch (rs = .756, α = .030) during spring but a non-significant, negative trend was observed for common carp in both seasons (rs = −.357, α = .385 spring; ρ = −.539, α = .168 autumn). Our results show that eDNA is an effective tool for the detection of single or multiple species to complement the traditional approaches using physical capture. As with all survey methods, the eDNA approach suffers from imperfect detection. We conclude that eDNA survey results are more powerful when used in conjunction with other survey methods as a way to enhance detection rates and increase confidence in the monitoring results.

Early detection and monitoring of invasive species is important for the development of effective measures directed at minimising the negative effects of invaders. In the early stages of invasion, aquatic invasive species are typically rare and their detection using costly and time-consuming field surveys is often challenging. Environmental DNA (eDNA) methods are increasingly applied in freshwater systems to detect and quantify target species with relative ease over large geographic scales and across the invasion fronts. In this study we test eDNA detection and quantification methods for invasive zebra and quagga mussels. Both mussel species have invaded widely in North America and Europe and show strong negative ecosystem-wide impacts. We extracted DNA from filtered water samples which we collected along the Rhine catchment in Switzerland, Germany and The Netherlands, including the known invasion area of the zebra mussel and the invasion front of the quagga mussel. Standard PCR and quantitative PCR (qPCR) methods were compared for detection and qPCR was used to quantify the eDNA signal for each species. Our results show that the invasion front of the quagga mussel has moved southwards, including areas where this species had not been detected previously with traditional benthic invertebrate sampling methods. Standard PCR and qPCR showed a similar performance in detecting both mussel species. Moreover, the eDNA quantification of the two species showed low variance within sampling site and matched with expected densities of zebra and quagga mussels based on previous field survey studies. The tested eDNA methods are cost effective and have the potential to be widely applied for the surveillance of zebra and quagga mussels in the future.

Silver carp (Hypophthalmichthys molitrix), an invasive planktivorous fish species in North America, pose a threat to aquatic ecosystems throughout the Mississippi River Drainage. These fish are well known for their airborne leaps in response to passing watercraft, but the trigger for, and functional significance of jumping remains unknown. The behavior of wild silver carp responding to moving (16, 24, 32, and 40 km/hr) 6 m aluminum boats equipped with 4-stroke outboard motors (100 or 150 hp) was quantified. Experiments were conducted at three sites on the Illinois River near Havana, IL and most boat transits (57.9%) stimulated five or more fish to jump. The frequency of jumping (fish/min) w as independent of speed and motor type and the vast majority of fish (> 90.0%) jumped after the boat had passed their position but avoided the area directly astern (< 4.0 m). Furthermore, 79.8% of fish vectored away from the moving watercraft. The results suggest that jumping direction is not random and fish can localize the stimulus source. The “delayed” jumping until after the boat had transited the area indicates that the trigger may be turbulence and/or higher sound pressure levels. This is the first study to model silver carp jumping in response to motorized watercraft and can aid fisheries managers in predicting the direction and location of airborne fish to develop effective herding and capture methods.

The biopesticide, Zequanox®, is registered for dreissenid mussel control in open water systems in the United States. Previous toxicity trials with nontarget organisms, including several young-of-the-year fish species and invertebrates, demonstrated selectivity of Zequanox for dreissenid mussels, but data are lacking on the treatment-related effects on reproduction and early life stage development of fish. The present study evaluated the effects of Zequanox on spawning and early life stages of the fathead minnow, Pimephales promelas, after exposure to the maximum approved concentration [100 mg active ingredient (AI)/L] and exposure duration (8h) for open water application. The results showed no significant treatment-related effect of Zequanox on survival, condition, or cumulative egg production (21 d) in adult fathead minnow. Eggs (≤24 h old) exposed to Zequanox developed to the eyed-stage at a similar rate to that of untreated eggs. Additionally, Zequanox did not have a significant effect on survival and growth (90 d) of newly hatched larvae (≤24-h old). Zequanox may be an option for control of dreissenid mussels in localized open water habitats where concerns exist regarding reproduction and recruitment of cyprinids and related species.