The bait worm Marphysa victori Lavesque, Daffe, Bonifácio & Hutchings, 2017 was originally described from Arcachon Bay, France. In the original description, the authors suggested that it may have been introduced, although definitive evidence was lacking at the time. In this paper, we confirm that M. victori is an exotic species originating from East Asia, probably a native of China or Japan. This species was most likely introduced into Arcachon Bay in the 1970s with non-native oysters Crassostrea gigas Thunberg, 1793. The Asiatic origin of this species is confirmed based on both morphological and molecular evidence. Comparison of the type specimens of M. victori with those of Marphysa bulla Liu, Hutchings & Kupriyanova, 2018 described from the Yellow Sea, China, showed no morphological or molecular differences and therefore the more recently named M. bulla is relegated to a junior synonym. This is the first example of a large-sized errant invertebrate species being introduced with oysters into Arcachon Bay.

The presence of shells of the Atlantic rangia, Rangia cuneata, a brackish-water species native from the Gulf of Mexico also known as gulf wedge clam, was reported in 2017 on the French coasts of the English Channel, in the waterway that connects Caen to the sea. However, no information was available on whether a population of this alien species had successfully established in the region. Here, only empty shells—except for one live individual—were sampled in that waterway, and the sampling was shifted to the nearby marina of Ouistreham, where water is mesohaline (6.89 ± SD 0.06 PSU). In spring 2017, the mean density in the marina reached 110.45 ± 86.08 ind m^-2, largely dominating the benthos community. The population was mostly composed of fairly large individuals, with no young-of-the-year found inside the marina. The modal values of the size frequency distribution ranged between 35 and 40 mm shell length. The growth patterns determined from the annual rings suggest a maximum lifespan of eight completed years. Following the assumption that colonization occurred at the larval stage, as in other European countries, this population may have established in 2009, i.e. only four years after its first detection in Europe, in the Antwerp harbour. The specimens collected are the largest recorded in European waters, suggesting a highly suitable environment for the species in the region. Given the invasive potential of Atlantic rangia within the last decade, a close monitoring of this population and of the spread of the species in French and European waters appears necessary to determine its impacts on these ecosystems.

The frequently high abundances achieved by the nonindigenous Asian clam, Corbicula fluminea, has caused concern regarding the potential negative ecological impact the clams may have on native benthic macroinvertebrate communities. This study examined the ecological consequences of C. fluminea establishment on the benthic macroinvertebrate community in a New Hampshire, USA, river by comparing the benthic community before and after establishment and comparing sites with and those without C. fluminea. The nonmolluscan benthic communities were sampled using a ponar grab and compared using community metrics of macroinvertebrate densities, taxa richness, Shannon diversity, Hilsenhoff Biotic Index, and Bray-Curtis similarities cluster analysis and MSD ordination. Native bivalves were sampled by divers excavating 0.25 m² quadrats and compared using abundance and size-frequency distributions. No consistent significant difference was seen when comparing macroinvertebrate metrics before vs. after C. fluminea establishment or when comparing sites with and without C. fluminea for any of the metrics used. Metrics were often similar or improved at sites with C. fluminea relative to years before establishment or when compared to reference sites lacking C. fluminea. Bray-Curtis cluster analysis and MDS ordination failed to separate sites with vs. those without C. fluminea. Similarly, native bivalve abundances, namely Elliptio complanata and Sphaeriidae, were similar at sites with vs. sites without C. fluminea. Elliptio complanata size-frequency distributions did not differ significantly when compared across sites with and without C. fluminea. Rather than having negative consequences on the benthic macroinvertebrate community as many have proposed, it appears that C. fluminea may either have no effect or positive effects on the macrobenthos.

Zebra mussels, Dreissena polymorpha, introduced to US freshwaters in 1986, have expanded into at least 19 Texas reservoir lakes since 2009. In Texas, they occupy the lowest latitudes in their North American and European range where summer surface water temperatures can exceed their upper thermal limit of 30 °C. Little is known of its population dynamics in such warm-water bodies, knowledge of which will be important for development/implementation of effective mussel management strategies. Zebra mussels were first discovered in Belton Lake, central Texas, in 2013 and developed a dense population by 2014. Belton Lake mussel settlement dynamics were studied from March 2016 to May 2017 on steel chains vertically suspended from a floating marina dock. Three chains were deployed at bimonthly intervals with mussel densities recorded monthly thereafter at each meter of depth until experiment termination. Shell growth rates and densities were also determined for emersed mussels at various sites in the reservoir after a 52-day period of high water. Spring cohort settlement occurred from June to September 2016 and fall cohort settlement from November 2016 to May 2017. Peak spring and fall cohort settlement densities were 1,025 mussels m^-2 on July 2016 and 175 m^-2 on February 2017, respectfully. Bottom to surface hypoxia from August (51.58%–71.14% DO) to October 2016 (49.04%–52.13% DO) extirpated the spring cohort by September 2016 and delayed fall cohort settlement until December 2016. Mean mussel settlement density increased with distance downstream from 0 mussels m^-2 in the reservoir’s shallow, inlet end to 21,160 mussels m^-2 at its deeper wider outlet end suggesting that mussel densities tend to be greatest in deeper, wider, low-flow, down-stream ends of impounded water bodies. Mean mussel shell growth rates across six sites were 127.9 μm day^-1, one of the fastest recorded for mussels in Europe and North America. Two annual reproductive periods, rapid growth rates and early maturity are likely to lead to zebra mussel population expansion to problematic sizes within 1–2 years after introduction into warm southwestern water bodies, leaving little time for development / implementation of effective mussel macrofouling control/mitigation strategies. Thus, development of effective macrofouling management/mitigation plans should be undertaken prior to establishment of mussels in a water body.

We conducted two mesocosm experiments to determine how invasive zebra mussels affected phytoplankton community and size structure in the summers of 2014 and 2017. Water containing natural phytoplankton and zooplankton communities was collected from the eutrophic Lake Mikołajskie (Masurian Lake District, northeastern Poland) and used to start each experiment. We analyzed how the introduction of zebra mussels impacted chlorophyll and the biomass of individual algae taxa, with particular interest on cyanobacteria. The starting phytoplankton communities differed in the two study years, whereby cyanobacteria dominated in 2014 and dinoflagellates and diatoms dominated in 2017. The biomass of crustacean zooplankton (cladocerans and copepods) was not affected by zebra mussels; therefore, we attributed differences in phytoplankton between treatments to the presence of zebra mussels. Zebra mussels had contrasting effects on cyanobacteria in the 2014 and 2017 experiments. In 2014, zebra mussels decreased cyanobacteria, while in 2017 they had a positive effect on cyanobacteria chlorophyll. The contrasting effects of zebra mussels on cyanobacteria could be related to differences in starting nutrient concentrations and phytoplankton communities between the two experiments. Filamentous green macroalgae dominated at the end of the both experiments in the zebra mussel treatments while they were not very abundant in the controls. Therefore, zebra mussels can have indirect negative effects on higher trophic levels even when they decrease cyanobacteria because they shift the autotrophic structure in favor of attached green macroalgae, which are a poor resource for zooplankton.

Habitat modification and the establishment of non-native species are two major causes of biodiversity loss. Reservoirs modify habitat, can restrain the occurrence of native species, and allow the establishment of non-native undesirable organisms. Non-native species are widespread. However, the status and distribution of some invaders in these man-made systems remains unclear, especially in the Neotropics. In this study, we surveyed digital databases to determine the distribution of non-native molluscs in Brazilian reservoirs. Studies on non-native molluscs in Brazilian reservoirs had been increasing steadily until they reached their peak in 2015. Eight non-native mollusc species were recorded in reservoirs in all river basins except for the Amazonas River. Non-native molluscs were reported in 74 reservoirs, mostly located within the Paraná River basin. The co-occurrence of multiple non-native molluscs was common. Time lapsed since first introduction of species was not correlated with their distribution in Brazilian reservoirs. This study was a first step toward understanding the distribution of non-native molluscs, and their possible impacts, in Neotropical reservoirs.

Laboratory experiments have indicated that tench (Tinca tinca) is an effective predator of Potamopyrgus antipodarum. However, few P. antipodarum have been found in the gastrointestinal tracts of wild caught benthivorous fishes, including tench. This had led to the assumption that the shell properties of the snail act against native predators. In general, it has been predicted that this is due to P. antipodarum possessing a thicker shell and a lower amount of soft tissues than native snails; the latter will thus be preferred by benthivorous fishes. In the current study, shell-crushing resistance and the soft tissue mass / shell mass ratio were compared between the non-native P. antipodarum and three native species. Results indicated a similar shell-crushing resistance for P. antipodarum relative to the native Bithynia tentaculata, the latter of which is a common food object in tench diet. However, the soft tissue mass / shell mass ratio of the invader was significantly lower than in most of the studied native snails, indicating a lower amount of soft tissues in P. antipodarum.

The killer shrimp (Dikerogammarus villosus) is one of the most recent and damaging aquatic invasive species in many parts of Europe, but information on how the species responds to predation pressures in recently invaded areas is very limited. We employed an open test arena to examine anti-predatory behaviour in killer shrimp exposed to either blank water or water conditioned with kairomones from the three-spined stickleback to simulate a predator threat. Killer shrimp spent much more time hiding in the presence of stickleback kairomones than when they were exposed to blank water. However, no significant difference was found in aggregation behaviour, and killer shrimp were strongly attracted to the scent of conspecifics regardless of predator threat. Given the strong selective pressures that fish predators can exert on native and invasive gammarids, our findings highlight the need to consider prey-predator interactions to better predict the dispersal and likely impact of killer shrimp into invaded ecosystems.

The Upper Paraná River Basin (UPRB) is harmed by several human activities, among which species introduction is particularly intense, making it the Neotropical ecoregion with the highest number of non-native fish species. Leporinus tigrinus Borodin, 1929 is a native species of the Tocantins-Araguaia River Basin and was recorded for the first time in the UPRB in 1999. Since then, the species was progressively recorded in lower portions of the UPRB (downstream Corumbá River). Therefore, the aim of this study was to provide evidence of possible introduction, establishment and dispersion of the species in that region. For this purpose, an inventory of its occurrence was performed by sampling ichthyoplankton, juveniles and adults of fishes in tributaries of the Porto Primavera Reservoir, as well as by compiling data from scientific collections considering all the UPRB. Diet and reproductive aspects were also analyzed. Overall, 23 specimens of L. tigrinus (10 adults and 13 juveniles) and five eggs (identified by DNA Barcoding) were sampled, evidencing the occurrence, reproduction, and recruitment of this species in the basin. The results of this study support the conclusion that L. tigrinus is an introduced species in the lower portion of the UPRB, capable of dispersing over long distances by passing through several reservoirs and dams (from upstream to downstream), possibly via turbines, spillways, locks, and fishways. Its dispersal pathway differs from the patterns observed for most invasive fish species in this basin, and suggests a substantial downstream dispersion through dams, even in the absence of fishways.

The life-history traits of a non-native population of Shimofuri goby (Tridentiger bifasciatus) were investigated in Nansi Lake, which is a storage lake on the East Route of the South-to-North Water Transfer Project, China. The results were analyzed in combination with data from other non-native populations of this species to reveal the life-history traits that caused its successful invasions. Mature gonads in April and May suggest that the species spawns in this period, and cohort tracking and age analysis revealed that individuals had a one-year lifespan. The relative fecundity was 2,825 ± 614 eggs/g. A short lifespan and high fecundity are opportunistic life-history traits that may enhance population establishment by promoting population increase. The male-biased sex ratio (except in April and May when the males guarding the nests) and sexual size dimorphism observed in this population may be important for males protecting nests and eggs, which is a typical equilibrium trait that facilitates establishment by increasing offspring survival. Non-native populations of this species in the San Francisco estuary system have been reported to batch spawn, have a lifespan of two years, and spawn during March and August, which in comparison with the population in Nansi Lake suggest that the species’ life-history traits are phenotypically plastic. We propose that the combined equilibrium and opportunistic characteristics of the species’ life-history traits and their plasticity facilitates successful invasions. Our results provide crucial information when evaluating the invasion risk of a species from its life-history traits.

Xenopus laevis has been present in the Chilean Mediterranean region since at least the 1970s. Studies of the global invasion of the African clawed frog have paid little attention to its early life stages, whose environmental requirements and threats are different to those of the adults. This study provides evidence of the vulnerability of X. laevis to Gambusia holbrooki, as well as information about its phenological development. Reproduction of X. laevis in Chile occurs between October and the end of April (austral spring to autumn). An overlap of early and late stages of larvae indicated variability within a clutch. The more recent establishment of G. holbrooki in Antumapu irrigation reservoir has resulted in a collapse in the reproduction and adult populations of X. laevis at this site.