Within impounded sections of the rivers Rhine and Meuse, epibenthic macroinvertebrate communities are impoverished and dominated by non-native invasive species such as the zebra mussel (Dreissena polymorpha) and quagga mussel (Dreissena rostriformis bugensis). In the winter of 2012 management of the water-level resulted in a low-water event in the River Nederrijn, but not in the River Meuse. Low-water levels persisted for five days with average daily air temperatures ranging from -3.6 to -7.2˚C. We assessed the effects of this low-water event on settled dreissenid mussel populations using a before-after-control-impact (BACI) design. Desiccation had a negative effect on the overall density of dreissenids. Six months after the water level recovered, mussel density had increased slightly. After 18 months, mussel density had recovered to pre-event level. Mussels collected after the event were smaller than specimens collected before the event, indicating re-colonization originating from upstream river sections. At the control site, the dreissenid populations showed no significant change in density or shell size distribution. In total, 99.4% of empty shells washed up and sampled directly after the low-water event consisted of invasive bivalves, including zebra mussel, quagga mussel and Asian clams (Corbicula fluminea and Corbicula fluminalis). The high number of empty dreissenid shells stranded on the river banks directly after the event coincided with a mass mortality of mussels in the littoral zone. Imposing a sudden water-level drawdown during severe winter conditions could be a tool for the temporary reduction of invasive mollusc density in impounded river sections. Full recovery of the population structure likely may require a period of two to three years. Therefore, we recommend that the long-term effects of recurrent water-level drawdowns on the diversity of invasive and native species be assessed.

Predictive modelling of species’ distributions is an important tool in biogeography, evolution, ecology, conservation, and invasive-species management. In this study we applied four different algorithms: Mahalanobis Distance, Domain, GARP and MAXENT, using them to predict the potential distribution of Limnoperna fortunei, a freshwater mussel native to Southeast Asia and a major fouling pest of water supply systems in Hong Kong, Japan, and South America. For model input, we compiled native and invaded occurrence data from Asia (71 points) and South America (248 points) from the literature and BIOCLIM’s environmental layers related to air temperature and precipitation. To evaluate model quality we used different “training” and “test” data sets. On the Mahalanobis Distance and Domain algorithms, three sets of training data were used: 1) Asia points; 2) South America points; 3) Asia and South America points. For MAXENT the combinations were: 1) South America points (25% test data/75% training data); 2) Asia points (25% test data/75% training data); 3) South America training data/Asia test data; 4) Asia training data/ South America test data; 5) Asia + South America points (25% test data/75% training data). Comparing the responses of the four types of algorithms used, it was found that MAXENT was the most conservative model (i.e. it produced a smaller area of suitable habitats) followed in order by GARP, Domain and Mahalanobis Distance, which proved to be the widest. In general, the best results corresponded to models in which the points of occurrence covered a greater environmental variability (Asia+South America 25% test data/75% training data). They showed better performance for predicting correctly the occurrence of regions already known to host the species. An ensemble map was produced based on the best scenarios for each algorithm. This tool performed well in assessing the potential global distribution of L. fortunei even though it was generated from climatic macro variables without the use of locale-specific abiotic variables, which are more difficult to obtain.

The ‘killer shrimp’, Dikerogammarus villosus, has been recognised as one of the 100 worst alien species in Europe, in terms of negative impacts on the biodiversity and functioning of invaded ecosystems. During the last twenty years, this Ponto-Caspian amphipod crustacean has rapidly spread throughout Europe’s freshwaters and its invasion and continued range expansion represents a major conservation management problem. Although a great deal of research has focussed on this almost ‘perfect’ invader as its damaging impacts, realised and potential, have become evident, we now present the first comprehensive review of D. villosus taxonomy, morphology, distribution, community impacts, parasites, life history, physiological tolerance and finally, possible eradication methods. We show the direct and indirect ecosystem impacts of this invader can be profound, as it is a top predator, capable of engaging in a diverse array of other feeding modes. It can quickly dominate resident macroinvertebrate communities in terms of numbers and biomass, with subsequent large-scale reductions in local biodiversity and potentially altering energy cycling, such as leaf litter processing. This damaging European invader has the potential to become a key invader on a global scale as it may be capable of reaching North American freshwaters, such as the Great Lakes. One positive aspect of this invader’s spread and impact is increased interest in alien species research generally, from decision-makers, stakeholders and the general public. This has resulted in greater financial support to study invasion mechanisms, preventative measures to stop invasion spread and ways to minimise damaging impacts. Our review provides a specific example, that studies identifying management strategies that mitigate against a potential invader’s spread should be undertaken at the earliest possible opportunity in order to minimise potentially irreversible ecosystem damage and biodiversity loss.

Invasive species are considered the second largest threat to native biodiversity, and ecosystem function and services. One pair of global invaders, bighead, Hypophthalmichthys nobilis, and silver carp, H. molitrix, (collectively referred to as Asian carps) have been introduced throughout the world, and are invading three prairie stream tributaries to the Missouri River in the United States. There is a paucity of knowledge and understanding about Asian carp population characteristics and biology in North America. As such, we documented spatial and temporal trends in population dynamics (i.e., density, size structure, age, growth and condition) of Asian carps in three tributaries to the Missouri River in South Dakota: Big Sioux, James and Vermillion from 2009 to 2012. Finally, native planktivore (i.e., gizzard shad, Dorosoma cepedianum, bigmouth buffalo, Ictiobus cyprinellus, and emerald shiner, Notropis atherinoides) characteristics were examined using condition (Fulton’s K). Overall, 469 silver carp and eight bighead carp were collected using boat electrofishing and mean catch-per-unit-effort of silver carp increased annually. The three rivers’ populations were similar in length frequencies. Silver carp growth was faster initially than later ages and overall was slower than Middle Mississippi River populations. Recruitment of silver carp was erratic with the 2010 year class dominating 91% of catches. Silver carp condition was also similar across rivers, seasons, and years. South Dakota silver carp populations were predicted from a length-weight regression to be lighter than the Gavins Point reach population of the Missouri River, and heavier than both the middle Mississippi and the Illinois River populations. Additionally, mean catch-per-unit-effort for bigmouth buffalo and emerald shiner decreased over the study period. Continued monitoring and research on this newly invading population of Asian carps will provide additional invaluable insight into complex invasive species, assist with understanding Asian carps population dynamics during and after an invasion, and expose the potential negative impacts Asian carps may be having on prairie stream ecosystems.

The invasion of Ponto-Caspian taxa in Western Europe has increased steadily since the connection of the Danube basin with the Rhine basin in 1992, in combination with transfers through interbasin shipping. In 2010, the tubenose goby (Proterorhinus semilunaris) and round goby (Neogobius melanostomus) were observed in Belgium for the first time. To gain insight in the introduction pathways in Belgium and to identify potential source populations, a phylogeographical and parasitological study was initiated on both species. The mitochondrial cytochrome b gene was sequenced, its haplotype diversity calculated and a statistical parsimony haplotype network built. Both species exhibited low haplotype diversity compared to native and other non-native populations. The network revealed potential source locations in the Northern Black Sea for the round goby and in the Danube at the Serbian-Romanian border for the tubenose goby. Fins, gills and body were examined for the presence of ectoparasites. Prevalence, abundance and infection intensity was much higher in tubenose goby, which might be the consequence of a different introduction pathway. Our data provides evidence that tubenose goby entered Belgium through active dispersal. The round goby, however, was most likely introduced with ballast water.

Pumpkinseed (Lepomis gibbosus) is listed among the most invasive fish species and has been demonstrated to have adverse impact on native species when present in high numbers. However, not all introductions result in high density populations. There are several possible underlying mechanisms behind this variation in population density (e.g. water quality, availability of nesting substratum and biotic interactions), but their relative importance remains poorly known. With this in mind, we studied vital rates (i.e. growth, maturation and reproduction) of pumpkinseed in 19 isolated standing waters of different pumpkinseed density. The fish were collected in early summer to determine their density, sex, age, growth and reproductive effort as well as environmental variables (i.e. availability of nesting substratum, acidity, nutrient concentrations, fish assemblage structure). To construct a population projection model with which to assess the relative importance of each vital rate for the growth of the populations, a stable population structure was assumed. Most environmental variables that affected vital rates (e.g. pH effect on individual growth) had little effect on population growth, or the associations were spurious (e.g. the negative effect of nesting substratum availability on gonad production). The environmental effects were dictated by a strong density dependent feedback of pumpkinseed density on the growth of age 2 fish, and gonad size and maturation state. This finding has important repercussions for management of pumpkinseed invasions: if only part of the population is removed or if complete eradication is followed by a re-introduction, then the population will rapidly recover to its former size. It was not possible to identify environmental drivers of pumpkinseed survival because the data had to be pooled across populations in order to estimate survival rates. However, a negative correlation was found between pumpkinseed and predator density, indicating that predator-induced mortality may be key in determining pumpkinseed invasiveness. Although the measure still needs thorough evaluation, introduction of native piscivores, especially northern pike (Esox lucius), may be a suitable way to prevent pumpkinseed from becoming the dominant species and reduce damage to local biodiversity.

The combination of global warming, resource exploitation and the resulting increase in Arctic shipping activity are expected to increase the risk of exotic species introductions to Arctic waters in the near future. Here, we provide for the first time a benthic invertebrate survey for non-indigenous species (NIS) from the Canadian Arctic coasts, incorporating historical information to identify new records. The top three ports at highest risk for introduction of NIS of the Canadian Arctic were surveyed: Churchill (Manitoba), Deception Bay (Quebec) and Iqaluit (Nunavut). A total of 236 genera and species were identified. Based on cross referencing comparisons of contemporary and historical information on species composition and distributions, 14.4% of the taxa identified can be considered new records within the port regions surveyed and 7.2% within the more extended, adjacent surrounding regions. Increased survey effort is the most likely explanation for the majority of new occurrences, however, a small number of records (n=7) were new mentions for Canada and were categorized as cryptogenic since we could not confidently describe them as being either native or introduced. Further research is required to better understand the status of these new taxa. This study provides a benchmark for early detection for benthic invertebrates in the region. Significant costs and intensive labor are involved in monitoring and in early detection surveys, but they provide a great opportunity for identifying native and introduced biodiversity, crucial to analyzing the changes taking place along one of the longest coastlines in the world, the Canadian Arctic coast.

This year-long study, covering three main seasons of India, focused on enumerating the effect of varying cover of Alternanthera philoxeroides (alligator weed) on the associated macrophyte species diversity of the littoral region of natural pond ecosystem. A total of 192 quadrats were randomly placed in the littoral region of 12 similar ponds containing varying degrees of A. philoxeroides infestation to estimate A. philoxeroides ‘cover (%)’ and number of associated macrophyte species in each quadrat. Overall, 20 associated macrophyte species, including 16 aquatic/littoral-associated, 2 non-aquatic species, and grasses and sedges, were found to be present. A. philoxeroides infestation was categorized into 4 cover grades (Grade I-IV) from lowest (no/negligible: <10% cover) to highest (>60% cover). For each season, significant differences in the total number of associated macrophyte species across the 4 A. philoxeroides cover grades were found. A Poisson-regression model showed that for each season, even when the effect of other invasive species was adjusted, the number of associated native macrophyte species in a quadrat decreases significantly with increase in A. philoxeroides cover. A comparison of the quadrat communities between the lowest grade (Grade I) and highest grade (Grade IV) of A. philoxeroides infestation showed a significant reduction of species richness, diversity and evenness from the lowest to the highest infestation grades. Again, Mann-Whitney U tests further revealed that the number of native macrophyte species was significantly lower at highest (Grade IV) A. philoxeroides infestation than that at lowest infestation (Grade I). The presence of multiple invaders in A. philoxeroides infested aquatic ecosystems is also reported, indicating probable facilitative interactions between A. philoxeroides and other invasive species. The socio-economic valuation of some important native plants, which were found to be significantly reduced at high infestation levels of A. philoxeroides, has also been highlighted.

The presence of an invasive species can either have a negative effect on pollination of natives by competing for pollinators or a positive effect since they may act as ‘magnet’ species facilitating pollinator visits to co-flowering species. We studied the plant-pollinator interactions for Ludwigia grandiflora, a highly invasive aquatic weed in Europe. First, a food web approach was used in one field site and our results showed an integration of L. grandiflora into the native plant-pollinator network with a dominance of L. grandiflora in terms of frequency of pollinator visits. Second, an experiment was designed to identify the pollinator guild of invasive L. grandiflora and native Lyhtrum salicaria and to measure interspecific pollinator switching. We also estimated the pollinator-mediated effect of high relative abundance of L. grandiflora (% cover of L. grandiflora) on L. salicaria plants. We monitored species composition, abundance and foraging behaviour of pollinators on L. salicaria. In addition, we assessed seed set per fruit of L. salicaria. Competition for pollinator services between invasive L. grandiflora and native L. salicaria seems minor as there was no evidence for decreased pollinator visitation or seed set of L. salicaria. On the contrary, more pollinators were recorded on L. salicaria plants when the cover of L. grandiflora was high compared to the control plants thereby indicating a facilitation effect, however this was not reflected in seed set. Despite the fact that L. grandiflora is well integrated in the native plant-pollinator network and highly attractive to pollinators, there was no evidence of negative impact of L. grandiflora on pollination of a native plant.

In 2010, Dutch stakeholders signed a code of conduct to prevent the introduction and spread of aquatic invasive plant species. This voluntary agreement between the government and horticulture sector (i.e. plant nurseries and retailers) has the objective to ban the sale of invasive species and to increase public awareness and stakeholder involvement in measures to prevent new introductions of potential invaders. Public outreach campaigns included flyers and posters displayed in stores and labelling of non-native plant species with warning logos and messages on harmful effects and appropriate disposal. We evaluated several measures issued in the Dutch code of conduct by performing ex ante and ex posterior surveys and interviews with relevant stakeholder groups. Compliance of retailers and producers concerning species on sale and proper labelling was monitored annually by the Netherlands Food and Consumer Product Safety Authority. Interviews with aquarists and water gardeners provided the first quantitative evidence in the Netherlands that 2–3% of these hobbyists deliberately introduced non-native aquatic plants in surface water. A survey of retail professionals identified limited availability of information and lack of salesman’s knowledge on the species lists issued in the code of conduct as major impediments for their engagement. Furthermore, low frequency of meetings and lack of guidance were major obstacles identified by the partners assembled in the code of conduct. Overall, compliance to species bans showed promising results, however, problems were identified with correct labelling of species. We conclude by listing opportunities to improve voluntary regulations for preventing non-native species introductions.

An estimated 60–75% of the world’s infectious diseases of humans are zoonotic, infecting both humans and other animals. Many are vector-borne, relying on transmission by mosquitoes and biting flies that are aquatic for much of their lifespan. Others rely on aquatic molluscs, fishes, or other aquatic animals for completion of their transmission cycles, and others develop and thrive in diverse freshwater environments outside any host. While such diseases remain firmly endemic in many areas, new outbreaks of infectious diseases associated with freshwater have occurred throughout the world, and many others have spread to new locations. This may involve introduction of aquatic vectors into locations where the disease was previously unknown, as in the recent occurrences of mosquito-transmitted diseases such as West Nile Virus in North America, dengue fever in southern Europe, Chikungunya virus in the Caribbean and South America, and dirofilariasis in Central and Eastern Europe. Such a pattern is also possible with such major human pathogens as Schistosoma blood flukes and food-borne trematodes, through introduction of aquatic host snails from long-established foci in other areas. Alternatively, waterborne pathogens may be introduced directly, leading to disease outbreaks such as the cholera disaster still unfolding in Haiti. Accidental or intentional introduction of pathogens or their aquatic vectors and hosts are among the primary concerns that affect international trade, travel, and global health security. These concerns are compounded by the prospect of warming climate, potentially resulting in primarily tropical diseases encroaching into historically subtropical or temperate regions. Thus, we must be prepared for the possibility of geographic spread of diseases into areas where they have not occurred, or reintroduction into areas where they once occurred but have been eliminated through control measures. For example, North America and Europe are at risk for reintroduction of such major “tropical” diseases as malaria and yellow fever, and thus must come under increasing scrutiny, starting with surveillance of freshwater systems for both established and potentially invasive vector and host populations. This critical perspective paper briefly reviews selected previous cases in which aquatic invasive species have contributed to infectious disease emergence, re-emergence, or increase, and proposes One Health strategies for integrating human, animal, and environmental monitoring and surveillance to better prepare for or prevent geographic spread of major human health threats associated with aquatic systems.