The occurrence of the non-indigenous species Limnoperna securis belonging to Mytilidae family is recorded for the first time in the Bay of Biscay. Numerous individuals were collected in intertidal and shallow waters in the inner part of Nervión estuary (Bizkaia, Basque Country, SE Bay of Biscay). In the present paper, notes about the history of this small brown mussel invasion, vectors of introduction and dispersal, as well as consequences of invasion are discussed.

The western tubenose goby, Proterorhinus semilunaris, of Ponto-Caspian origin, already recorded in 2002 from the lowest course of the Dutch River Meuse, was caught upstream for the first time in 2008 in the Border Meuse, the river-stretch forming the border between Belgium and the Netherlands. In 2009 it reached the upstream extremity of the Border Meuse in Wallonia and in 2010 it was recorded in Flanders, in a canal connected to the Border Meuse. Discussion is provided about its migration pathway. Further upstream expansion of the western tubenose goby may be expected in less man-modified and lightly navigated sections of the River Meuse, e.g. those lined with macrophyte-rich habitats. Behavioural competition with the native bullhead Cottus perifretum is likely and might lead to a decline in the bullhead population.

The invasive ctenophore, Mnemiopsis leidyi, which had its first mass occurrence in Limfjorden (Denmark) in 2007, and the indigenous common jellyfish, Aurelia aurita, were studied from autumn 2008 through summer 2009. By December 2008, both A. aurita and M. leidyi populations had disappeared for the winter. In 2009, the first A. aurita appeared in February and the medusae attained their maximum umbrella diameter by the end of June, when the estimated half-life of copepods was only 1.6 ± 1.1 d. Low densities of M. leidyi in early July (< 0.5 m^-3) increased to high densities by late August (66.2 to 224.9 ind. m^-3). In 2009, the estimated time to clear the central part of Limfjorden (Skive Fjord) of zooplankton by A. aurita and M. leidyi feeding was between 0.5 d (4 June) and 2.9 d (26 August). During that period, copepods and other mesozooplankton organisms were virtually absent while ciliates were a substantial part of the zooplankton biomass. In "pre-Mnemiopsis years", there seems to have been large variability in the grazing impact on zooplankton depending on the seasonal abundance of A. aurita. With the addition of the second carnivore M. leidyi, however, additional predation pressure caused the zooplankton stocks to be severely depressed throughout 2008 and 2009 when copepods and cladocerans no longer showed the high seasonal peaks in abundance typical of previous years.

The predatory neogastropod Ocinebrellus inornatus was first reported from Europe in W France in 1995 and has since been detected at other sites in NW and N France and The Netherlands. It is native to the North Pacific where it preys on the Pacific oyster Crassostrea gigas. Here we report on the occurrence of the species in beds of European oysters (Ostrea edulis) in the Limfjord, NW Jutland, Denmark. The morphology-based identification has been confirmed by genetic analysis. The species was probably introduced with oysters imported from France in the 1970s and 1980s. The invasion is still relatively localized but as the species has established a reproductive population, it may eventually spread to other parts of the fjord and in time pose a problem to the oyster fishery. The species’ invasion history is reviewed.

No crayfish species are native to the Colorado River Basin (CRB), including the portion of the state of Colorado west of the Continental Divide. Virile crayfish [Orconectes virilis (Hagen, 1870)], a recent invader in the middle Yampa River in northwestern Colorado, displayed an abrupt increase in abundance in the early 2000s, which coincided with a drought, a severe decline in the abundance of small-bodied and juvenile native fishes, and a dramatic increase in the abundance of nonnative smallmouth bass [Micropterus dolomieu (Lacepède, 1802)]. The annual density of virile crayfish was 6.4/m² in 2005 and 9.3/m² in 2006. The annual biomass density of virile crayfish was 9.0g/m² in 2005 and 15.8 g/m² in 2006, representing a riverwide biomass of 122 kg/ha, which equaled that of other macroinvertebrates and fish combined (120.7 kg/ha). Efforts to recover and preserve native fishes in the Upper Colorado River Basin (UCRB), particularly in the Yampa River, have been hampered by nonnative predatory fishes, but the implications of crayfish may have been overlooked and underestimated. Stream conditions during the drought apparently facilitated proliferation by virile crayfish in the middle Yampa River, likely contributing to hyperpredation on native fishes by invasive smallmouth bass. This trophic interaction between virile crayfish and smallmouth bass, in conjunction with regional projections for climate change, will likely make efforts to reduce the abundance and negative ecological impact of smallmouth bass in this ecosystem more difficult and costly. Given the nonnative status of all crayfishes in the CRB, and their invasive capacity and potential to negatively reconfigure native lotic food webs, all states in the UCRB should prohibit the importation, movement, sale, possession and stocking of any live crayfish.

We present an event-tree biological risk assessment for a non-native Atlantic salmon (Salmo salar) invasion into Alaskan waters. Atlantic salmon farming is prohibited in Alaska, USA, but large numbers of them are reared in ocean net-pens in Washinton (WA) USA, and British Columbia (BC), Canada. Large numbers of Atlantic salmon escape each year, and they have been recovered in both saltwater and freshwater in WA, BC, and Alaska. There is limited evidence of successful spawning and rearing in BC, but none from Alaska. No stream-reared smolts are known to have returned successfully from ocean migrations, but survey efforts for escaped adults and reared juveniles in streams have been very limited in time and space. Given recurring, large-scale escape events, propagule pressure could be great enough in any given year for a successful invasion. To date, such large numbers of adults have not been recorded ascending Alaskan streams, but again, monitoring is very limited. Atlantic salmon could most likely successfully spawn and rear in Alaskan streams, so successful ocean migration appears to be the factor most likely to limit their success. Successful invasion of BC waters, where propagule pressure is greater, followed by a subsequent invasion of a pre-adapted stock by straying to Alaskan waters, may pose the greatest risk. The lack of adequate surveys, under-reporting of escapes and recoveries, and inherent ecosystem variation, make it impossible to assign meaningful probabilities to the risk of an invasion of Alaskan waters. We conclude that the short-term risk of invasion generally appears low, but that it might increase over time. We also note that invasion is only part of the ecological risk of Atlantic salmon farming in Pacific waters. Disease, parasites, and pollution may also pose risks to local ecosystems – we do not assess these risks here.

We set out to explore whether the inclusion of perceptions into risk assessment might be a key to unlocking the human factor in the vectoring of aquatic non-indigenous species. To this end, we developed a risk assessment model that used people’s perception of concern and stated behavioural intentions to measure consequence. We trialled this risk model using a test scenario of the non-indigenous species Didymosphenia geminata (a freshwater diatom) being introduced to Tasmania, Australia: a location where it is currently not present. Likelihood was determined by calculating the probability of Didymosphenia entering the test region based on exposure to D. geminata (travel history of arriving air passengers and the passenger’s participation in freshwater recreational activities) and mitigation activities (whether their recreational equipment had been washed). The likelihood of a Didymosphenia incursion into Tasmania was determined to be rare. Consequence was determined by targeting three recreational user groups that participate in activities related to the movement of this species in other countries: trout anglers, hikers, and kayakers. Consequence was measured as respondent’s level of concern and stated behavioural intentions if the respondent was confronted with an incursion of Didymosphenia. The consequence of a Didymosphenia incursion ranged from moderate to catastrophic. Thus, the total derived risk was determined to be low-medium. The use of perception to inform the consequence component of the risk assessment proved useful as individuals behaviours are often attributable to the introduction of species, and thus are an important consideration for risk management and education. At a local level these outcomes provide direction to biosecurity of unregulated pathways. At a global level, this risk assessment is a useful tool to assess the potential vectoring of a non-indigenous aquatic species, and potential human actions that might impede the management of a non-indigenous species once it crosses a border.

The catadromous Chinese mitten crab (CMC), Eriocheir sinensis is well known for its extensive invasion routes across the world. However, little is known about both adult and juvenile behaviour after they arrive to a new region. Particularly if the CMC has utilised freight ship ballast tanks as its invasion vector to new freshwater areas like coastal connected larger lakes. The Swedish Lake Vänern, Europe’s third largest freshwater lake, offers a suitable study area since only a handful of CMC had been reported between its first record in 1954 and 2004. Hence, the increased catch of of CMC in the mid 2000s was unexpected and provided a rare opportunity to study the initial phase of a biological invasion. Fortunately local fishermen have traditionally, since the mid 1970s, utilised large stationary fish trap nets, evenly distributed from the inlet to the harbour of Lidköping outward into the main part of the lake. During the peak occurrence in 2005 the traps captured CMC frequently for 90 days starting on August 10. Daily catch increased from September 19th to October 17th. Thereafter the number decreased until November 7th when the last crab was captured. Only one crab out of the 21 caught in the two traps furthest away from the harbour inlet was caught before September 19th. The number of caught CMC differed significantly between the trap nets. Almost half (48.4 %) of all CMC were caught in the two traps closest to the harbour inlet and 41.9% in the second trap-line, consisting of two traps 6 km from the harbour inlet. The remaining crabs were caught in the traps furthest away. Catch pattern from this unique invasion event is discussed in relation to CMC dispersal/migration, invading sample size, behavioural traits and catch efficiency of traps.

Gammarus varsoviensis is morphologically close to G. lacustris, with which it is often misidentified. Geographic range of G. varsoviensis includes Germany, Poland, Lithuania, Latvia, Belarus and Ukraine. Such a distribution pattern led us to the assumption that the species might have originated in the Black Sea drainage area. From there, as early as the nineteenth century, it could possibly have migrated to the Baltic basin through the Pripyat-Bug canal. Thus, the goals of this study are: (1) to indicate the level of genetic divergence of G. varsoviensis from the morphologically closest species – G. lacustris and (2) to investigate the possibility of the Pontic origin of G. varsoviensis and its range expansion across the Black Sea/Baltic Sea watershed to Central Europe through the artificial canal network. Altogether 128 partial 16S rDNA sequences of Gammarus varsoviensis from 19 localities were gained. They were analysed in conjunction with a sequence of G. lacustris obtained in this study from the Dnieper system and sequences of G. lacustris, G. pulex and G. fossarum available in GenBank in order to estimate the relationships among the species. GenBank accession numbers for all the haplotypes defined within this study are: G. varsoviensis – from JN641868 to JN641875; G. lacustris – JN641876. The genetic distance within and between the species was calculated, as well as phylogenetic relationships among haplotypes, which were inferred with Neighbor-Joining method. The haplotype relationships were analysed with the Minimum Spanning Network. Also mismatch distribution of the haplotypes were tested under sudden expansion model and sequence deviations from selective neutrality. Neighbor-Joining analysis revealed that G. varsoviensis and G. lacustris haplotypes formed separate well defined clades. Mean genetic diversity between the two species was ca. 15× higher than the intraspecific distance and similar to the value obtained for G. fossarum/G. pulex species pair. Therefore, G. varsoviensis can be definitely considered as a distinct species from G. lacustris. Among 128 sequences obtained from G. varsoviensis, 8 haplotypes were identified and grouped into two clades: one found only in the lower Dnieper (two haplotypes) and the second one encompassing the rest of haplotypes observed in the upper Dnieper and Baltic Sea basin. Only one haplotype was found in the Baltic Sea drainage area. A mismatch distribution curve as well as selective neutrality tests demonstrated sudden expansion model. Our findings suggest that G. varsoviensis is an alien gammarid that originated in the Pontic area. Its expansion in Central Europe apparently started soon after the opening of the artificial waterways joining the Black and the Baltic Sea drainage basins.

We offer a case study showing: a) the susceptibility of the Truckee River and Lake Tahoe to an invasion by the New Zealand Mudsnail (Potamopyrgus antipodarum) and b) the short-term impacts on periphyton standing crop in the Truckee River and Lake Tahoe as a result of grazing by New Zealand mudsnails. Snail survivorship in the Truckee River experiment ranged from 50–85 percent across treatments and snail survivorship ranged from 5–40 percent in the Lake Tahoe experiment. Periphyton standing crop was negatively affected in both snail density treatments of the Truckee River experiment but the results were mixed in the Lake Tahoe experiment. Our results suggest that the Truckee River is more vulnerable to establishment by New Zealand mudsnails than Lake Tahoe.

Following the discovery of New Zealand mudsnails, Potamopyrgus antipodarum, in the Silver Creek watershed in Idaho, we investigated the distribution and dynamics of the snail populations over two years in field surveys. Despite extensive fishing and recreational activities in the watershed, the infestations appeared limited in extent. As with other published studies, densities of P. antipodarum were highest during summer months, but the distribution in Silver Creek was patchy. We found that near-to-below freezing winter water temperatures in localized reaches of the watershed were related to reduced populations or lack of detection. Distributions observed in winter were associated with regions of groundwater releases, or downstream of impoundments that dampened the temperature extremes observed in locations elsewhere in the watershed. We speculate that the population has remained restricted because thermal conditions are not conducive to year-round survival and growth. However, these relationships could be altered with watershed alterations or global climate change.

The New Zealand mud snail, Potamopyrgus antipodarum, was found in four lakes and one medium-sized river located in the southern part of Lithuania during 2010. These are the first records of P. antipodarum from Lithuanian freshwaters, a considerable distance from the Curonian Lagoon wherein the species was reported during the 1950s. Available information shows that the species has invaded quite recently. Two morphotypes of the species, the regular and carinatus (keeled) forms, were observed in three lakes. The presence of separate morphotypes and variation in shell morphometry suggest multiple (at least two) independent invasion events, and species expansion on a local scale. The most abundant population of the invasive snail was recorded in Lake Dusia which is an inland lake of exceptional importance for staging and moulting of migratory waterfowl. Thus, the most probable vector of the invasion and local dispersal is ornithochory, while translocation with fish stocking material may also be operating. Further rapid expansion of the species in Lithuanian lakes and rivers seems very possible.

Meretrix lusoria supports an important shellfish fishery distributed around Japan and the southern coast of Korea. The species is considered to be either local extinct or endangered in Japan and in response to a decrease in availability in Japan, M. petechialis, a closely related species, has recently been imported from China and the Korean Peninsula. M. petechialis is currently defined as an “alien species” in Japan, has been released into habitats where the local species M. lusoria occurs. We conducted a survey and detected natural hybrids between M. lusoria and M. petechialis. Nineteen Meretrix spp. population samples were collected in Japan, China, and Korea from 2004 to 2006 (15 samples from Japan, two from China, and two from South Korea). Polymerase chain reaction-restriction fragment length polymorphisms in the cytochrome c oxidase subunit I region after HincII digestion and amplification of the nuclear gene ANT enabled identification of the two species. The exotic M. petechialis was found in Yoshinogawa and Kanonji, where periodically, large numbers of M. petechialis seedlings have been released. Combined results of RFLP and ANT individual genotypes suggest the existence of at least one hybrid individual and two putative hybrids between the Japanese local species M. lusoria and the continental alien species M. petechialis found in Chichibugahama and Kanonji. This is the first record demonstrating the existence of the alien species M. petechialis and of hybrids co-occurring with local M. lusoria in a natural habitat. Our results show that the alien species M. petechialis is currently relatively rare in Japan. If however, M. petechialis populations expand in the wild, they could replace the local M. lusoria and cause genetic disturbance via hybridization, as observed at one site (Kanonji, Kagawa Pref.). To conserve the endangered local M. lusoria resource, immediate controls of the release of M. petechialis will be necessary to prevent this species spreading and hybridizing with the native M. lusoria population.

Tolerance and adaptability to changing environmental parameters have made Nile tilapia Oreochromis niloticus (Linnaeus, 1758) a hardy and desirable aquaculture species. These traits have also enabled this fish to become a highly successful invasive species into temperate and subtropical aquatic environments. Otolith-based ages of Nile tilapia (41.3 – 400.0 mm TL, 1.34 – 1,293 g WW, n = 259) collected from a power plant cooling reservoir and the Pascagoula River proper indicated that feral populations overwintered reaching ages up to 4+ years old in coastal Mississippi, USA; these data confirm their establishment. A survey of mean daily winter (December – February) water temperatures from 2004 – 2010 in this region showed minimum lethal temperatures of < 10°C to occur nearly 11% of the time attesting to the adaptability of the Nile tilapia as an invasive species. One annulus (opaque zone) per year was being deposited from April to August based on marginal increment analysis along with sulcal groove length-age estimation of the young-of-the-year Nile tilapia. Additionally, life history metrics measured for this temperate population of Nile tilapia were nearly identical to those reported from African environments, indicating they are flourishing in this non-native habitat.

The invasive ctenophore Mnemiopsis leidyi A. Agassiz, 1865 was recorded for the first time in Northern Europe in summer 2005, while the first records in the North Sea date back to summer 2006. The first sightings in the Belgian part of the North Sea were made in August 2007 in the port of Zeebrugge, but most probably M. leidyi had already been present for a longer period in this area. The high densities in the port of Zeebrugge suggest that M. leidyi entered the Belgian marine waters via ballast water transport, comparable with the invasion in the Black and Caspian Seas and the Dutch part of the North Sea. In the period 2009–2011, M. leidyi was found in all ports and all along the Belgian coastline, up to 27 km offshore. Further offshore, no M. leidyi were found in zooplankton samples and small meshed otter trawl samples. Sightings of adult individuals in the coldest winter months imply that the species can survive Belgian winters. Highest densities (17 ind.m^-3) were found in the Sluice dock in the port of Oostende. Along the coastline, average densities of 0.4 ind.m 3 were recorded. As M. leidyi might previously have been misidentified on the basis of morphological features alone, we also determined the species with genetic identification tools. Taking into account the notorious impact of this species in its native and in other invaded waters, it is recommended to continue the monitoring of M. leidyi populations in the Belgian part of the North Sea.

The rusty crayfish, Orconectes rusticus (Girard, 1852), native to the eastern U.S., was discovered west of the Rocky Mountains in the John Day River in Oregon in 2005. In the five years since then, the known range of Orconectes rusticus has more than doubled to 145 river km along the mainstem of the river and populations have achieved high densities in several locations. To arrive at this estimate, the present study employed commercial crayfish traps, D-frame kick nets, and snorkel surveys to assess crayfish communities in the upper John Day basin. Natural dispersal, multiple introductions, a more thorough survey of the study area, or a combination of these factors could account for the expansion of the known distribution O. rusticus within the basin. The limit of O. rusticus expansion in the John Day River and broader Columbia River Basin, and the likely consequences for invaded ecosystems remain to be resolved.

The genetic variation among nine populations of the red swamp crayfish Procambarus clarkii was examined using partial sequences of the mitochondrial COI gene. Three populations (Illinois and Louisiana, United States and northern Coahuila, Mexico) represented the native range and six populations came from areas where the species has been introduced (central Coahuila, southern Nuevo León, Durango, Chihuahua and Chiapas, Mexico, and Cartago, Costa Rica). A 689 bp fragment was amplified from 37 samples. Uncorrected genetic distances among sequences were p = 0 to 0.02031 and 12 haplotypes were found. A phylogenetic reconstruction shows that the three populations from the native range remain very similar to each other and some introduced populations can be directly associated to one of them. The populations from Nuevo León, central Coahuila and Costa Rica were the most divergent ones. Overall the genetic variation found in P. clarkii in both native and introduced populations is low.

Melanoides tuberculata Müller, 1774 (Thiaridae), a freshwater prosobranch snail native to regions of Asia and Africa, was introduced into the U.S. in the 1960s and is now found in fifteen states. Melanoides tuberculata can affect native communities directly by displacing native snail species and indirectly by introducing foreign trematodes into novel environments. As the exact mechanisms of displacement of native snails by M. tuberculata are unknown, egg predation rates on native snails (Physella spp.) by two different size classes (>30 mm and <30 mm, total length) of M. tuberculata were determined in laboratory experiments. Additionally, M. tuberculata were sampled from Diamond Y Spring (Pecos County, TX) to determine if the exotic trematode Centrocestus formosanus (Nishigori, 1924) has been introduced into the system. No M. tuberculata > 30 mm were found to consume Physella spp. and only 2.8% of M. tuberculata snails consumed egg masses. None of the M. tuberculata collected from Diamond Y Spring were found to be infected with C. formosanus.

Recently specimens of the polychaete Marphysa sanguinea (Montagu, 1813) (Annelida: Eunicida: Eunicidae) were reported as an introduction to the Eastern Scheldt in southwestern Netherlands. In order to confirm the species identity, material was examined with SEM and compared with material from Devon near the type locality in Cornwall, UK. These studies confirmed that this was a new record of M. sanguinea, which can be distinguished from other Marphysa species by the pattern of the distribution of pectinate chaetae in posterior parapodia. This new record extends the known distribution of the species based on verified records, eastward along the English Channel. As the specimens from the Netherlands show additional variation, the species description of M. sanguinea is expanded, which will facilitate future identifications of this species and comparison with other members of the genus.

The present work reports the finding of an exotic bivalve, Barnea (Anchomasa) truncata, in the intertidal zone of the Bahía Blanca Estuary Argentina (38º Lat S), more than 2000 km south from the edge of its native range in South America (21º Lat S, Brazil). Lines of evidence suggest that larval transport by shipping is the probable entry route of this species. The most apparent modification created by the introduction of this species is the generation of greater complexity and habitat heterogeneity in the mud tidal plain of the estuary; the consequent effects on the local biota should therefore be evaluated.

The freshwater cnidarian Craspedacusta sowerbii, native to the Yangtze valley, has invaded lakes and ponds throughout the world. Most distribution records have to date been based on observations of the medusa (jellyfish) stage, including numerous recent publications. We aimed to determine whether polyps are widespread in lakes, and geographical areas, outside of where medusae have been observed, and whether constructed waters are more easily invaded than natural waters. Our results show that C. sowerbii is more common and widespread than is apparent from observations of medusae. We argue that observed occurrences of medusae provide little useful information regarding the distribution of this species, and that published records of new jellyfish occurrences provide unreliable estimates of the timing of introduction, establishment or spread of C. sowerbii in new regions. We found no evidence that constructed waters were more readily invaded than natural waters. Overall, accurate determination of Craspedacusta occurrence and distribution requires systematic surveys of the polyp stages.