The potential role of waterbirds in the dispersal of invasive apple snail Pomacea canaliculata was evaluated by feeding their eggs to mallards Anas platyrhynchos and quantifying the recovery of intact and viable eggs in their faeces and regurgitations. A total of 30,400 eggs were ingested by eight male mallards in 19 feeding trials. Endozoochory potential was detected in 14 trials, in which a total of 46 intact eggs were recovered from mallard faeces, and 684 intact eggs were regurgitated. Most intact snail eggs in faeces were egested 2–6 hours after feeding (72%), whereas 81% of those regurgitated were egested less than 1 hour after feeding. Two snail eggs from faeces and 74 eggs from regurgitations were successfully hatched (jointly representing 0.25% of ingested eggs). These data suggest that apple snail eggs can survive gut passage by waterbirds, and long-distance endozoochory events may contribute to the spread of the snail in the introduced range. In addition, short-distance dispersal is crucial and should not be overlooked as a means to sustain population, increase the extent of invaded range, and maintain gene flow.

Freshwater Japanese mystery snails (Cipangopaludina japonica, previously Heterogen japonica) were introduced to North America from Asia in the early 1900s and have colonized many lake and river systems across the United States (US). Tolerance to environmental stressors, such as desiccation, plays a large role in species’ invasion potential and persistence in novel environments. To characterize the desiccation tolerance of C. japonica snails, adults and juveniles from three eastern US populations were exposed to air for 13.5 weeks (adults, n = 650) or 48 hours (juveniles, n = 849) and their mortality assessed over time. Over 50% of adult snails from each population exposed to desiccation survived over 10 weeks of constant air exposure, while survival ranged from 10 to 64% at the end of the exposure experiment (13.5 weeks), depending on population, indicating exceedingly high resistance to desiccation mortality in adults of this species. In contrast, juvenile snails were much more vulnerable to desiccation, with over 70% mortality at just 24 hours of drying and only a single individual surviving 48 hours of desiccation stress. We found that the interaction between snail shell length and time affected survival for both adults and juveniles, where larger body sizes were associated with increased probability of survival as time of exposure increased (p < 0.001 for both juveniles and adults). Based on these data, juveniles cannot survive long-term air exposure, but the high desiccation tolerance of adults may facilitate survival and population persistence in stressful environments and allow for increased dispersal between water bodies. Therefore, both commercial and recreational users of water bodies containing introduced C. japonica should be aware of the risk of unintentional dispersal between water bodies via contaminated gear and/or boats, even if those materials are exposed to air for a significant amount of time.

The rapid increase in the arrival of tropical-origin species into the Levant region has dramatically changed local ecosystems. Non-indigenous species are known for their ability to utilize available ecological niches and in some events expand their non-native niche over time. Here, as an example of such expansion, we report on a massive colonization by the non-indigenous solitary ascidian, Microcosmus exasperatus (Heller, 1878), on soft bottoms along the Mediterranean coast of Israel. While this tropical-origin species is well-known for its ability to form dense aggregations on rocky substrates and artificial structures, only limited reports exist from soft-bottom habitats. In September 2022, a massive settlement of M. exasperatus was sighted on the sandy bottom (15–22 m depth) in front of Mikhmoret, Israel. M. exasperatus had settled on miniature “islets” of hard substrates, such as polychaete tubes, shells, or pebbles. By October, the population had reached a peak density, with a mean of 1.8±1.3 individuals m-2 (±95% confidence interval for the mean). Longshore visual surveys by towed divers revealed similar populations scattered along the central Israeli coast. Monthly compass surveys monitoring the population density, revealed a gradual population decline during late fall and winter, leading to a complete eradication in February 2023, probably due to a severe winter storm. No population was detectable throughout the spring but in August 2023 a few specimens were again detected on the sandy bottom, albeit at densities several orders of magnitude lower than the previous year. It is postulated that the ephemeral colonization of soft-bottom areas serves as “stepping stones” for the species’ dispersal into new habitats, potentially amplifying its invasive potential. Long-term monitoring across a more comprehensive depth range will reveal whether the observed massive colonization was a singular event or a recurring phenomenon that had previously remained unnoticed.

The Eleventh International Conference on Marine Bioinvasions (ICMB-XI), held May 15–19, 2023, in Baltimore, Maryland, USA, convened 213 attendees from 24 countries to discuss the challenges and advancements in managing marine non-indigenous species (NIS). The conference emphasized the urgent need for international collaboration to address the increasing threats posed by marine bioinvasions, which transcend geopolitical boundaries. Participants explored six key themes through 119 oral presentations, 37 posters, and six keynote speakers, providing a platform for researchers, policymakers, and industry professionals to exchange knowledge and strategies. Notably, ICMB-XI implemented the first Code of Conduct for the Society for the Study of Marine Bioinvasions, promoting inclusivity and ethical scientific discourse. Here, we review articles published in Aquatic Invasions and Management of Biological Invasions based on research presented at ICMB-XI. Studies highlighted novel findings on species settlement dynamics, NIS ecological impacts, and advancements in detection methods such as environmental DNA monitoring. Research also examined the role of climate change in facilitating NIS, the influence of biofouling on NIS establishment, and the expansion of NIS into new ecological niches. Beyond scientific discussions, ICMB-XI celebrated the intersection of art and science through a collaboration with artist April Flanders, whose work communicated the impacts of marine invasions to broader audiences. The conference also provided travel awards and student achievement prizes to support early-career scientists. As ICMB-XI concluded, participants reinforced the need for sustained, large-scale efforts to mitigate marine bioinvasions through enhanced research, policy integration, and cross-sector collaboration. The next ICMB, scheduled for 2025 in Madeira, Portugal, aims to continue advancing the field and fostering international partnerships in marine bioinvasion management.

Potamopyrgus antipodarum (Gray, 1843) has been considered one of the most successful and widespread invasive freshwater molluscs worldwide. This snail has been present in mainland Portugal since the 1960s, but there is only scarce information regarding its presence in Madeira or Azores archipelagos. In this work, macroinvertebrate communities were sampled in six Madeira Island streams. P. antipodarum was found in all sampled sites, with abundances ranging from 3 to 3528 individuals per sampling area, indicating that the species arrived at Madeira recently and is now in a clear spreading phase. Our results indicate no relationship between the abundance of P. antipodarum and macroinvertebrates’ biodiversity indices. Nevertheless, the abundance of P. antipodarum was extremely high in some locations, representing more than 30% of all benthic invertebrates, which triggered alterations in the food web and community structure. The future impacts of this invasion are for now unpredictable, but given P. antipodarum parthenogenetic reproduction and fast spread, its presence can potentially affect Madeira Island’s aquatic ecosystems’ ecological status and services. These results can inform environmental agencies on the importance of monitoring the presence and spread of this invasive species and call for management strategies focused on early detection and control measures. Given the endemicity and insularity of Madeira macroinvertebrate communities, the spread of P. antipodarum should be limited to mitigate its ecological impacts and biodiversity loss.

In October 2023 and April 2024, ecological monitoring was undertaken in brackish waters of the North Sea Canal, a major shipping route linking the Port of Amsterdam to the North Sea. Amongst the macrobenthic samples, four endemic and three non-native mysid species were recorded, two of the latter for the first time in this locality. This concerns the now globally distributed Deltamysis holmquistae, and the Mediterranean Diamysis lagunaris. Based on the spatial context, these specimens are highly likely to have been introduced through human-mediated transport, with shipping providing the most obvious entry path into the North Sea Canal. Both species were found in fully artificial and in restored near-natural habitats, highlighting their versatility as invasive species. Pictorial descriptions and complete keys for both species are included in order to facilitate future assessments of potential range expansions.

Zebra mussels represent one of the most pervasive and expensive non-native species to be introduced into new aquatic ecosystems, negatively impacting human structures and infrastructure and acting as ecosystem engineers. Zebra mussels have demonstrated thermal plasticity, enabling expansion to semi-tropical aquatic systems including Texas ca. 2009. In this study we described spawning and population dynamics and water quality changes after colonization of two central Texas reservoirs, Lake Austin and Lady Bird Lake, ca. 2017. Veliger concentrations peaked in spring and early summer (Julian days 120–170) when water temperatures were between 20–25 °C. Adult population densities were initially highest nearest the busiest boat ramps and peaked in 2019–2020. Densities declined thereafter in the lower sections, but generally increased upriver in Lake Austin. However, the decline throughout Lady Bird Lake was three orders of magnitude from the peak. After colonization, chlorophyll a and suspended solid concentrations significantly declined, concomitant with significant changes in water total phosphorus concentrations; changes in different nitrogen-form concentrations were mixed. However, water quality changes were exacerbated by changing discharge volumes. Recent drought conditions and reduced discharges after 2021 have also resulted in elevated water temperatures, notably in Lady Bird Lake, that may have contributed to observed declines in adult zebra mussel densities nearshore. We hypothesize that other southern United States reservoirs should expect similar variations in population dynamics which will impact municipal, recreational, and water quality attributes. Preventing introductions remains essential as the species continues to rapidly spread to new regions.

The introduction of non-native species can lead to competition with native species for key resources, driving the decline and extinction of endemic biodiversity. Recently, a newly discovered and evolutionarily distinct lineage of Korogwe tilapia (Oreochromis korogwe) was reported from small lakes in southern Tanzania. This small-bodied lineage is potentially threatened by introduced Nile tilapia (Oreochromis niloticus), an invasive large-bodied congeneric with a pan-tropical non-native distribution. Nile tilapia is known to dominate ecologically-similar native tilapia in competitive interactions, preventing access to resources such as food and shelter. We therefore hypothesised that competition between Nile tilapia and Korogwe tilapia could limit access to resources by the native species and hence reduce their growth rate, a key determinant of fitness. In this study, tilapia were collected from Lake Rutamba in two field seasons, and individuals were classified using microsatellite DNA genotypes as O. niloticus, O. korogwe or interspecific hybrids. Recent growth rate of these individuals was determined by measuring the distance between scale circuli. In contrast to expectations, we found that native O. korogwe overall had a faster growth rate than the invasive O. niloticus, with hybrids showing growth rates more similar to O. korogwe. We propose that in Lake Rutamba the persistence of O. korogwe could be partially enabled by a faster growth rate than the large-bodied invasive O. niloticus. Based on these results, we suggest that predictions of the effects of invasive species on native biodiversity may benefit from information on relative fitness, in addition to ecological niche overlap.

The tropical invasive freshwater cyanobacterium Raphidiopsis raciborskii, first recorded in Central Europe about two decades ago, is now a relatively widespread species, expanding its geographic range. Currently, however, there are no records of this species in Sweden. As a bloom-forming and toxin-producing species, future population growths of R. raciborskii could negatively affect local biodiversity and ecosystem services. Hence, there is an urgent need to understand the factors controlling its capability of establishment in Northern European lakes. We performed a laboratory experiment to study the competitive success of R. raciborskii when interacting with other phytoplankton from major taxonomic groups typically found in Scandinavian lakes (diatoms, green algae, and cyanobacteria). The experimental settings included three temperature conditions (17; 22; 26 °C) and three different nutrient conditions (N:P ratios 8:1; 16:1; 32:1). The experiment was performed in a semi-continuous culture setup to test the invasion success of R. raciborskii. Raphidiopsis raciborskii did not become the dominant species in any of the tested conditions; however, it was able to grow and maintain its biomass in all treatments, also in relatively low temperature (17 °C). Temperature played an important role in the phytoplankton community composition, especially for the cyanobacterial group. Raphidiopsis raciborskii was more successful than Planktothrix agardhii, but less dominant than Microcystis aeruginosa. Temperature is thus important in determining the potential survival and settlement of the invasive R. raciborskii in lakes.

The cryptogenic nuisance alga Chondria tumulosa was first observed in 2016 at Manawai (Pearl and Hermes Atoll) in the Papahānaumokuākea Marine National Monument. It has since spread across the atoll, growing in thick mats and smothering benthic habitat. In September 2021 the species was observed at Kuaihelani (Midway Atoll), ~130 km to the northwest. Due to its growth habit and recent spread, considerable concern has been raised and management of the species may be warranted. We used publicly available oceanographic data and the Connectivity Modeling System software to assess how the potential for successful dispersal of C. tumulosa is affected by particle properties and oceanographic conditions. We found the likelihood of successful transit to be linked to particle density, oceanographic conditions at the time of release, and release location. Further modeling explicitly targeted the capacity of both reproductive tetraspores as well as drifting fragments to disperse. Model results indicated tetraspores of C. tumulosa are unlikely to survive the transit from Manawai to Kuaihelani, as none arrived at Kuaihelani above the depth limit of the species and those arriving below successfully settled at a rate of only 0.02%. In contrast, fragments modeled as rafting on marine flotsam such as macroalgae and marine debris settled at a rate of 3.85%. Rafting fragments also settled ~600 km further to the southeast (towards the Main Hawaiian Islands) than tetraspores. This study identified oceanographic conditions and particle properties likely to aid dispersal of C. tumulosa to Kuaihelani and suggests that fragments rafting on marine flotsam may accelerate its spread.