DOI: 10.3391/ai.2026.21.3.199579

Authors: Seongjae Kim, Taekjun Lee, Jeounghee Lee

Abstract: The colonial bryozoan Watersipora subtorquata is a globally distributed non-indigenous species (NIS), posing increasing threats to marine biodiversity and coastal industries through biofouling and competition with native biota. In South Korea, despite its recognition as a harmful marine organism, few studies have addressed its ecological behavior under varying environmental conditions. This study investigated the spatiotemporal dynamics of W. subtorquata percent cover in four Korean harbors—Yangpo, Tongyeong, Bieung, and Jeju—over a 39-month period (April 2021 to July 2024). Standardized acrylic settlement plates and in-situ measurements of water temperature and salinity were used to evaluate percent cover patterns. Generalized Additive Models (GAMs) revealed temperature was significantly associated with percent cover across all four harbors, while salinity played a key role in Bieung. A significant interaction effect between temperature and salinity was observed in Jeju. These results provide novel insights into the environmental sensitivity of W. subtorquata, highlighting the importance of multi-regional and long-term monitoring to guide site-specific management of invasive species, while underscoring the need for higher-resolution environmental time series to assess climate-related implications more directly.

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DOI: 10.3391/ai.2026.21.2.190069

Authors: Michaela Palmieri, Leandro E. Miranda, Melanie R. Boudreau, Corey G. Dunn, Leslie M. Burger, Dennis Riecke

Abstract: Understanding spatial distribution patterns is essential to management of invasive species. Aquatic invasive species can be notably challenging to detect due to the substantial effort required to locate them underwater. This limitation has resulted in a lack of timely distribution maps, particularly over vast regions, and hindered efforts to understand, forecast, and manage the proliferation of invasive bigheaded carps (Hypophthalmichthys spp.). Much of the Mississippi River basin, particularly the Lower Mississippi Alluvial Valley, provides access to a massive network of interconnected floodplain lakes. In the absence of lake-specific monitoring data on carp occurrence status, we used local expert knowledge, provided by fish managers interviewed virtually, in conjunction with Maximum Entropy (MaxEnt) modeling, to predict bigheaded carps distribution in relation to lake physical characteristics. We predicted widespread carp invasion in more than 60% of over one thousand floodplain lakes, with lake size, inundation, and proximity to rivers closely related to carp presence. The resultant distribution map may be imprecise given the swift proliferation of bigheaded carps and sparse monitoring data, but it offers a baseline upon which presence data and range can be compared. This assessment method is also a resource for identifying priority management and conservation areas and can serve as a first step in conservation planning.

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DOI: 10.3391/ai.2026.21.2.189571

Authors: Zachary M. Schumber, Michael A. Baker, Brian J. Irwin, Martin J. Hamel, Peter D. Hazelton

Abstract: Aquatic invasive species (AIS) are amongst the greatest threats to native aquatic biodiversity. These introduced species often thrive in human-altered environments and spread through human-mediated pathways to invade new watersheds. Corbicula fluminea is a freshwater bivalve native to southeastern Asia first introduced in North America in Seattle, WA, in 1938 and has spread to nearly every major watershed in the southeastern United States. In the present study, we use an information theoretic framework to compare landscape and stream habitat variables associated with C. fluminea presence across five HUC10 watersheds in the upper Savannah River basin of South Carolina and Georgia, USA. Predictive models included landscape-level and site-level habitat variables associated with agricultural, developed, and forested landscapes. Models with variables associated with forested and developed landscapes were the top performing models based on AICc values. In top performing models C. fluminea presence was positively correlated with increased stream width, but negatively correlated with substrates dominated by cobble. Lower performing models highlight positive correlations with the presence of upstream reservoirs and increased developed landscape surrounding the site. Identification of habitat and landscape correlates with invasive species presence may lead to more efficient introduction monitoring efforts for conservation managers.

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DOI: 10.3391/ai.2026.21.2.187217

Authors: Mateusz Draga, Maciej Gąbka

Abstract: Light and temperature are critical factors for the growth of all plants, including invasive macrophytes. The high invasiveness of these species is often linked to their ability to outcompete native plants through greater shade tolerance and rapid growth at elevated temperatures. In our experimental study, we tested two hypotheses: (1) the high competitiveness of invasive alien macrophytes stems from their exceptional shade tolerance, and (2) although thermophilic invasive aquatic plants thrive in warm water, they retain the capacity to survive in colder conditions. To test these hypotheses, three invasive aquatic plant species: Elodea nuttallii, Cabomba caroliniana, and Vallisneria spiralis - were cultivated in two separate experiments: one testing low light conditions under constant temperature, and the other testing low temperature conditions under constant light. Each cultivation lasted seven weeks. Following this period, key morphological traits, including shoot length, number of offshoots, dry mass, and chlorophyll a content, were measured for each species. Our results show that all tested species were able to temporarily survive at 7 °C, although their growth was generally inhibited. E. nuttallii was the exception, exhibiting growth even at this low temperature. Moreover, V. spiralis and C. caroliniana demonstrated broad tolerance to varying light levels, while E. nuttallii thrived under low light conditions but exhibited reduced growth at higher intensities. Additionally, low temperature and light levels inhibited daughter ramet production in V. spiralis, while extremely low light induced partial necrosis in the lower parts of E. nuttallii shoots, possibly as a strategy to escape unfavorable light conditions. Overall, our research underscores the critical role of temperature in the development of invasive aquatic plants and confirms their high shade tolerance, a key factor in their competitiveness.

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DOI: 10.3391/ai.2026.21.1.183198

Authors: Victoria A. Van Mierlo, Stephanie J. Green, Craig A. Emmerton, Mina Nasr, Blake R. Stuparyk, Rolf D. Vinebrooke, Cristina Buendia, Faye R. Wyatt, Mark S. Poesch

Abstract: Aquatic invasive species are among the greatest threats to freshwater biodiversity. Crayfish are especially robust freshwater invaders that can compete on various trophic levels simultaneously. The Northern Crayfish (Faxonius virilis) was introduced to the North Saskatchewan River basin circa 1990. Their impact on Alberta’s native fish communities remains unknown. We sampled 10 North Saskatchewan River basin tributaries for F. virilis and six common native fishes. We used stable isotope analysis to investigate if there exists resource partitioning and/or competition between F. virilis and native fishes and whether F. virilis sympatry is related to differences in isotopic metrics/body condition of native fishes. Overlap (0.14–31.2%) of F. virilis and native species basin-wide isotopic niches indicated that F. virilis can potentially consume the same dietary resources as secondary consumer fishes. However, segregation of realized isotopic niches indicated no actual consumption of the same resources. Similarity in isotopic metrics/body condition of allopatric and sympatric native fish populations indicated that F. virilis sympatry did not have detectable negative trophic effects on native fishes. Thus, F. virilis may be using dietary plasticity to exploit a different trophic niche than native fishes, ergo, avoiding interspecific competition through resource partitioning.

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DOI: 10.3391/ai.2026.21.1.181535

Authors: Edward P. Levri, Gavin Suter, Gracie Harlow, Nicole Flanders

Abstract: The enemy release hypothesis is one of the best supported hypotheses to explain the success of invasive species. This hypothesis suggests that invaders are successful, in part, because they experience fewer natural enemies (i.e. predators and parasites) in their invaded range compared to their native range. The New Zealand mud snail (NZMS), Potamopyrgus antipodarum, is a world-wide invader that is highly infected by digenetic trematodes in its native New Zealand. Here we compared infection prevalence of NZMS from multiple locations in the eastern US to published infection prevalences in the native range, and we also compared the infection prevalences of NZMS to infection prevalences of coexisting native snails where coexisting natives were found. We found no NZMS infected with trematodes at any site. In the two locations with coexisting natives, we found at least some natives infected with trematodes, and in one of the locations, we found both natives and NZMS associated with the annelid, Chaetogaster limnaei. C. limnaei can exist as a parasite of mollusks in the renal organ, or it can be found in the mantle cavity where it can act as a mutualist, consuming parasites (i.e. miracidia) that may be trying to infect the snail. We found that NZMS were generally less associated with both forms than native snails, but the ectosymbiotic form was more prevalent than the endoparasitic form in NZMS (and most natives). This creates the possibility that the symbiont may be a net benefit to NZMS and could positively influence invasion success.

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DOI: 10.3391/ai.2025.20.4.171920

Authors: Quenton M. Tuckett, Katie M. Everett, T. Myles Domohowski, Jesse R. Blanchard, Jeffrey E. Hill

Abstract: Thermal tolerance can reveal the risk of establishment and spread for non-native tropical species introduced to more subtropical regions. These data are particularly important for novel introductions such as the Rio Cauca Caecilian (Typhlonectes natans), a species of amphibian established in Miami, Florida, United States of America (USA). To estimate its thermal tolerance T. natans individuals were captured with baited traps, transported to the laboratory, and acclimated to 25°C. We used chronic lethal methodology to estimate three cold tolerance endpoints: cessation of feeding, loss of equilibrium, and death. This methodology utilizes a 1°C per day temperature change which allows for stepwise reacclimation. Endpoints were 18.61°C ± 0.91, 17.08–20.56 (mean ± SD, range) for cessation of feeding, 13.61°C ± 0.81, 12.68–14.98 for loss of equilibrium and 12.45°C ± 0.49, 11.72–13.84 for death. The chronic lethal minimum temperature is relatively high for an established aquatic species in Florida, suggesting water temperature may limit its northward spread. Thermal tolerance attributes are one aspect of the risk of spread, and some information gaps remain, including salinity and desiccation tolerance, attributes that could allow movement between coastal watersheds and persistence in seasonal wetlands.

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DOI: 10.3391/ai.2025.20.4.175531

Authors: William Ota, William Budnick, Reuben Keller, Patrick Siwula, Brian Roth

Abstract: Invasive crayfish species have become a significant ecological concern in the Laurentian Great Lakes Basin, adversely affecting native biodiversity and ecosystem functions. This review synthesizes 24 years of peer-reviewed literature to elucidate crayfish invasion pathways in the Great Lakes. Over this period, the literature has highlighted natural dispersal and bait release as dominant invasion pathways for crayfish in this region, accounting for over half of reported cases. Emerging pathways, including the retail trade and accidental releases, underscore the evolving nature of invasion pathways. Research efforts have concentrated geographically in Wisconsin, Michigan, and Illinois, with limited studies addressing other Great Lakes states, revealing significant gaps to understand the full scope of invasion pathways. This review identified rusty crayfish (Faxonius rusticus) and red swamp crayfish (Procambarus clarkii) as the focus of much of this work while other species were not as prevalent in introduction pathways research. While historical studies have provided foundational insights, reliance on historical pathways data has limited our understanding of newer mechanisms, such as aquarium trade releases and species misidentifications in retail markets. To address these challenges, we recommend broadening the research focus of future work to encompass underrepresented regions and species, enhancing collaborative efforts among stakeholders, and improving regulatory oversight of retail trade practices. Public engagement is a critical component for mitigating the impacts of invasive crayfish through responsible consumerism and pet ownership practices. This comprehensive synthesis aims to inform future research efforts, policy development and surveillance initiatives, foster coordinated responses to invasive species threats, and contribute to the preservation of the Great Lakes Basin’s ecological integrity.

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DOI: 10.3391/ai.2025.20.4.164778

Authors: Crosby K. Hedden, Caroline E. Mallinson, Crystal Castillo, Alexander D. Loubere, Ryan D. Mann

Abstract: The New Zealand mudsnail (NZMS) is a small-bodied gastropod that has successfully invaded waters across multiple continents. This species has the ability to reach extremely high densities in streams and exclude other aquatic macroinvertebrates which higher trophic levels rely on as a food source. While the effects of NZMS are well studied, early detection methods for this species are limited almost entirely to environmental DNA (eDNA) testing. While eDNA is a valuable tool for the early detection of this species, low density sampling protocols are also essential to verify positive eDNA detections and to determine precise distributions so that management may be implemented in these areas during an invasion. The goal of our study is to evaluate and compare the efficacy of various quadrat sampling protocols to detect NZMS at low densities, and to determine the densities below which detection may become uncertain using these protocols. We tested 10-, 20-, and 30-quadrat grids within 100 m stream reaches, using both random and strategic selection of quadrat sites, to assess each design’s performance in overall probability of detection. We found that a non-random strategic sampling design was significantly more effective at detection of NZMS than a random design. Additionally, we found that, across study streams with different snail densities, taking 14 quadrat Surber samples using non-random strategic site selection consistently led to capture probabilities over 99%, with one exception in the stream with the lowest densities. To account for heterogeneity in habitat and snail density, we recommend using 30 quadrats with non-random strategic site selection to maximize detection in systems with unknown presence. This study outlines a sampling protocol to verify the physical presence of NZMS that can be adapted into monitoring programs or to confirm presence of this species following a suspected introduction.

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DOI: 10.3391/ai.2025.20.4.175069

Authors: Yang Zhao, Qichen Zhang, Andy J. Green, Sixian Tang, Xiaodong Jiang

Abstract: 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.

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DOI: 10.3391/ai.2025.20.3.161320

Authors: Shoujie Tang, Ying Xing, Temesgen Tola Geletu, Jinliang Zhao

Abstract: In recent decades, the redbelly tilapia (Coptodon zillii) has become one of the most serious invasive alien fish species worldwide. The successful invasion of this fish may largely depend on the plasticity of its life-history traits. In order to explore the life-history traits of the invasive population of C. zillii, we chose Shuikou Reservoir of Minjiang River, China, as a typical invasive habitat, and 1,041 specimens were collected monthly from March 2023 to February 2024. Life-history traits were systematically investigated. The results showed that the entire population consists of individuals from age 1 to age 6, with the highest percentage (95.10%) of younger individuals at 1–2 years old. The sex ratio of males to females was 1.05:1. The equation of the length-weight relationship was W = 0.048*L2.938, and the parameters of von Bertalanffy growth equation were L∞= 32.937 cm, W∞= 1381.010 g, k = 0.131, and t0 = -2.056. The breeding season ranged from March to November, and the minimum sexually mature standard lengths of females and males were 8.7 and 9.0 cm, respectively. Mean absolute fecundity was 3854.38±254.43 eggs, while mean relative fecundity to standard length and body weight were 301.95±16.94 eggs/cm and 60.44±3.56 eggs/g, respectively. These results indicated that the population of C. zillii in Shuikou Reservoir presented characteristics such as a high proportion of young individuals, low growth rate, long spawning season, high fecundity, and smaller size at first maturity compared with the native and other invasive populations. Both opportunistic and equilibrium life-history strategies might have contributed to their successful invasion, and there is a potential risk of further population expansion.

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DOI: 10.3391/ai.2025.20.3.152950

Authors: Erin S. McCallum, Kristina M. Sefc, Tomas Brodin, Patricia Burkhardt-Holm, Karen Bussmann-Charran, Ann-Britt Florin, Juergen Geist, Michal Janáč, Pavel Jurajda, Jake M. Martin, Joachim Pander, Aneesh P. H. Bose

Abstract: River barriers such as hydropower dams and weirs can negatively affect river ecosystems by disrupting connectivity and reducing biodiversity. However, such barriers could also limit the spread of invasive species. Here, we used a spatial population genetics approach to test whether river barriers act as a hindrance to gene flow in the invasive round goby (Neogobius melanostomus Pallas, 1814). We sampled gobies from four different rivers across their invasive range in Central Europe (the Danube, Dyje, Morava, and Rhine rivers), with locations on either side of eight major river barriers. Using microsatellite genotyping, we found that round goby populations were differentiated with increasing number of river barriers and with increasing distance between sampling sites, depending on the river system in focus. We found significant population differentiation across three individual barriers, but no clear indication that this was related to barrier type as barriers were highly diverse. We also found reduced genetic diversity in populations that were more recently established. Our findings suggest that successive river barriers can sometimes slow the spread of round goby. Further research on the features of barriers that hinder round goby movement will help to design barrier passage solutions that will both limit spread of this invasive species and maintain connectivity for the native fauna.

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DOI: 10.3391/ai.2025.20.3.153638

Authors: Carter S. Cranberg, Reuben P. Keller, Joseph R. Milanovich

Abstract: Modeling current and future distributions of aquatic invasive species is an important approach for mitigating and preventing invasions in freshwater ecosystems. Two invasive crayfish species of concern in North America are Procambarus clarkii and Faxonius rusticus, which each pose significant biological and economic threats. In this study, we used MaxEnt to model current and future (2050 and 2070) distributions for both species under two climate change scenarios. Our present-day models highlight areas in North America where both species are being under-sampled and likely to thrive, while our future models reveal changes in habitable regions. The future models for P. clarkii reveal general expansion (up to 66.38%) in potential habitat, while models for F. rusticus reveal general contraction (down to -13.62%); however, all future models show northern shifts in potential habitat from the present-day models. Variables related to temperature played the largest role in habitat predictability, underscoring the relationship between climate change and new aquatic invasions. Understanding how different climate change scenarios can influence habitat availability for these two crayfish species can help in targeting management efforts for current populations and preventing future spread.

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DOI: 10.3391/ai.2025.20.3.160924

Authors: Xiaolong Huang, Heyun Wang, Songyang Li, Leyang Xu, Zhaoshi Wu, Hu He, Kuanyi Li

Abstract: As global warming continues, increasing minimum winter temperatures may no longer limit the northward expansion of invasive species, particularly those from tropical zones. A mesocosm experiment with a chronosequence approach (space-for-time trade-off) was used to examine the effects of water level variation on the traits of the invasive aquatic plant water hyacinth [Pontederia crassipes (formerly Eichhornia crassipes)] collected from freezing, chilling and warm overwintering locations in China. We hypothesized that the phenotypic plasticity of the plant, particularly its ability to adjust its root morphology and topology in response to vernal water level rise, enhances its capacity to invade freshwater ecosystems. The results revealed significant plasticity in the response of the plants to water level, with plant traits such as total biomass, diaspore number, leaf area, specific leaf area, root length, and photosynthetic efficiency significantly increasing under a 10-cm water level, which can be regarded as a moderate overwintering water level. However, the plants from the warm location did not perform better than did those from the freezing or chilling locations, possibly because the harsh winter conditions reduced plant biomass but did not negatively affect the plants at the gene level. These findings highlight phenotypic plasticity in rooting behavior, which enables plant survival and growth during overwintering in the littoral zone, allowing P. crassipes to withstand low temperatures and to rapidly proliferate during the vernal water rise period. This study highlights the importance of early detection and management strategies to control the spread of P. crassipes, particularly given the trends in global climate change, which may facilitate its northward expansion. The use of P. crassipes as a model plant is recommended for studying the responses of invasive aquatic plants to global change in freshwater ecosystems.

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DOI: 10.3391/ai.2025.20.3.162564

Authors: Efim D. Pavlov, Tran Duc Dien, Ekaterina V. Ganzha

Abstract: Non-native suckermouth armoured catfish Pterygoplichthys spp. have spread extensively across many river systems in Vietnam. It is possible that their expanded distribution occurred through the brackish waters of estuaries and coastal zones, facilitating movement from one river system to another. It has been previously hypothesized that, for successful dispersal through brackish water, armoured catfish can tolerate changes in water salinity and are capable of avoiding high salinity levels that threaten their survival. In this study, we experimentally estimated the movements and the directions of juvenile and adult wild loricariids in fresh and brackish water. Our results showed that juveniles exhibit a circadian rhythm of locomotor activity similar to that of adults. However, juveniles display a more pronounced reaction to increasing water salinity ‒ at 5 PSU ‒ while adults respond at 15 PSU. This likely explains the absence of juveniles in natural brackish water environments and their reduced potential to spread through brackish waters compared to adults. Adult loricariids are likely capable of recognizing and avoiding high-salinity zones (>10 PSU) by increasing locomotor activity, predominantly directed toward the surface. Their ability to grasp air helps maintain positive buoyancy, allowing them to remain in the surface layer of freshwater over extended periods of time. Variability in salinity tolerance among adults (ranging from 2 to 16 hours in 15 PSU) may enable some individuals to be more successful in dispersing through estuaries and along coastlines.

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DOI: 10.3391/ai.2025.20.2.152871

Authors: Anna J. Phillips, Jason Reilly, Don Ashton, Dennis J. Richardson, Makiri Sei, William E. Moser

Abstract: The Common North American Turtle Leech, Placobdella parasitica, was reported in 2023 using the Northwestern Pond Turtle, Actinemys (Emys) marmorata, as a host in the Lower Rogue River, southwestern Oregon, USA. Molecular analysis and haplotype networks based on the mitochondrial cytochrome c oxidase subunit I (COI) gene sequence revealed that this introduced population has very low haplotype diversity and is likely the result of a single introduction of a gravid adult, an adult brooding eggs or hatchlings, or a small number of related individuals. While we determined that the precise source population was not represented in our sampling, there was strong similarity between the representatives from Oregon and those from near the Arkansas-Missouri border. Molecular evidence also supports this as a recent introduction, likely via human activity, and potential pathways of introduction are considered. Our results agreed with a previous study of morphological and molecular data of P. parasitica samples from throughout its native range in North America that found the species to be widely distributed, morphologically conservative, and molecularly variable. Using COI sequence data with Bayesian Inference, we evaluated species cohesiveness using species delimitation analyses (ABGD, mPTP, bPTP, and GMYC) that revealed 13 species entities that were clustered by geographic region. Identifying the source population and possible invasion pathways of this introduced population and assessing the dispersal capabilities of P. parasitica could slow and prevent further range expansion in the western USA. Introduced P. parasitica has not been recognized as a threat to the health of the Northwestern Pond Turtle or the Rogue River ecosystem so its presence has not been systematically monitored, but any introduced parasite is concerning given that the U.S. Fish and Wildlife Service has proposed this turtle species for Threatened status under the Endangered Species Act.

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DOI: 10.3391/ai.2025.20.2.153557

Authors: Wen Xiong, Wei Zhang, Zhen Deng, Peter A. Bowler, Kang Chen, Baoqiang Wang

Abstract: The Yellow River is the second largest river in China and it supports a rich biodiversity and numerous endemic fish species (Atrilinea macrolepis, Brachymystax lenok tsinlingensis, and Hucho taimen). It is one of China’s most important freshwater aquaculture and mariculture regions, and many non-native species have been introduced into the region. This study provided the Yellow River Basin’s first and current list of non-native aquatic species including a total of 112 species comprised of 59 fishes, 27 aquatic plants, 21 Mollusca, three reptiles, one crustacean and one amphibian. The primary introduction pathway is aquaculture (69 species), followed by the aquarium and ornamental trade (30 species), forage (four species), unintentional introductions (four species), ecological restoration (two species), religious releases (two species), and one species for biocontrol. Asia is the primary geographic origin of non-native species (39 species), followed by North America (33 species), South America (16 species), Europe (10 species), Africa (nine species) and Oceania (five species). Many non-native species have become important species in local aquaculture, the aquarium and ornamental trade or for other human uses. Many non-native species have caused significant negative economic, ecological and societal impacts. More research, field investigations and new guiding policies should be applied for the effective control and management of non-native species in the Yellow River Basin.

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DOI: 10.3391/ai.2024.19.4.141420

Authors: Brent J. Bellinger, Stephen L. Davis

Abstract: 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.

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DOI: 10.3391/ai.2024.19.3.131793

Authors: Jason L. Locklin, Josiah S. Moore, Robert F. McMahon

Abstract: Zebra mussel (Dreissena polymorpha) population dynamics were recorded between 2 September 2019 and 26 September 2020 at marina sites in each of two adjacent central Texas water bodies, Belton (BL) and Stillhouse Hollow (SHL) Lakes infested in 2013 and 2016, respectively. Lake water temperatures were insignificantly different while dissolved oxygen, pH and Secchi Disk depths were slightly higher in SHL. Veliger densities in both populations peaked in late Fall 2019 with veligers becoming absent by January 2020. Veliger densities again peaked in May-August 2020. These fall and spring spawning periods resulted in the presence of fall and spring mussel settlement cohorts. Mussel densities on settlement plates were greater at SHL than BL. At both sites, Fall 2019 cohorts had a lifespan of approximately one year or less, experiencing mass mortality during peak water temperatures in late summer/early fall the year after initial cohort settlement. Shell growth rates of the Spring 2020 BL and SHL cohorts were 91.4 and 67.3 µm/day, over a 126 day growing period, respectively, falling within the range reported for mussel populations in other southwestern US water bodies. Rapid shell growth and maturation allowed initiation of spawning earlier than zebra mussel populations in cooler, higher latitudes. Rapid growth and early maturity allows southwestern US zebra mussel populations to rapidly attain peak densities after infestation followed by population declines as recorded in BL. That southwestern mussel populations rapidly attain post invasion peak densities allows little time for water using facilities to develop effective, environmentally acceptable means of protecting infrastructure from mussel fouling. Thus, plans to prevent/minimize mussel fouling should be made in advance of invasion. Similarly, water body managers should develop and implement plans to minimize invasion likelihood and for rapid response before invasion occurs.

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DOI: 10.3391/ai.2024.19.3.134082

Authors: Shaina R. Myers, Hailey E. Germeau, Meghan McCann, Wyatt Cranston, Charles M. Crisafulli, Kena Fox-Dobbs, James E. Gawel

Abstract: Mount St. Helens National Volcanic Monument was designated by the U.S. Congress in 1982 to conserve the landscape for natural regeneration, scientific research, education, and cultural resource preservation. However, this designation has not eliminated threats from the introduction of non-native species. The non-native New Zealand mud snail (NZMS), Potamopyrgus antipodarum, was first observed in 2016 along the SW shore of Spirit Lake at the foot of Mount St. Helens, despite the lake’s closure to public recreation and isolation from other known sites harboring NZMS. Our study mapped native and non-native snails on aquatic macrophytes in Spirit Lake, analyzed NZMS eDNA in Spirit Lake and surrounding waters, measured stable isotopes in snails and their food sources, and analyzed rainbow trout (Oncorhynchus mykiss) gut contents from a twenty-year survey to examine the patterns of spatial distribution, habitat occurrence, and resource use. Our results show that NZMS colonies were likely first established along the SW shore of Spirit Lake in 2015, and presently remain largely confined to the vegetated littoral zone along this same shoreline. The native snail species Gyraulus deflectus and NZMS co-occur on multiple macrophyte species, and δ¹⁵N and δ¹³C isotope data reveal they are consuming the same food sources, but no evidence was seen for competitive exclusion. The abundance and frequency of NZMS found in rainbow trout gut contents have increased since 2015 with a significant portion undigested. In addition, stable isotope analysis shows a negligible trophic tie between snails (both NZMS and G. deflectus) and rainbow trout, which may signal longer-term impacts on fish populations. Characterizing this invasion spatially and temporally elucidates the factors facilitating and hindering the spread of NZMS in a relatively young and dynamic subalpine lake ecosystem closed to public recreation, and may inform current and future management decisions.

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DOI: 10.3391/ai.2024.19.2.124660

Authors: Matthew R. Pintar, Nicole D. Strickland, Jeffrey L. Kline, Mark I. Cook, Nathan J. Dorn

Abstract: Asian swamp eels (Monopterus albus/javanensis) were first reported as introduced to Florida waterbodies in 1997 near Tampa and Miami; a third population was recorded by 1999 in Homestead. Initial assessments, published soon after swamp eels in southern Florida were first recorded in wetlands beyond canals and ponds (in 2007), concluded there was little threat to Florida’s aquatic ecosystems. Long-term data now suggest they precipitated population crashes of crayfishes and small fishes in the eastern Everglades. We used records from continuous long-term monitoring programs, sporadic monitoring studies, and online databases to reconstruct swamp eel presence across Florida. Monitoring studies provided wetland hydrologic variables to assess limits for swamp eels. From 1997–2007, populations in southern Florida remained restricted to canals; initial spread from 2007–2017 across southern Everglades National Park proceeded slowly and the two populations covered ~1500 km2 of southern Florida. From 2017–2022, the rate of spread increased as they spread west and north (~5800 km2 range). Through 2014, the Tampa population occurred only along southern/eastern Tampa Bay (~60 km2) but has since spread south along the Gulf Coast, east into central Florida, and south along the Lake Wales Ridge (~11,000 km2). We found evidence of two potentially new introductions, in Palm Beach County and Orlando. There was no clear evidence of limitation of wetland drying on swamp eel occurrence in the Everglades; they were captured in marshes that dried for 1–5 months during the previous dry season, but short-hydroperiod wetlands may have slowed spread. In the Everglades, evidence suggests swamp eels may have been inadvertently spread into marshes from canals used to deliver water for flood control and hydrologic restoration. Swamp eels are currently spreading unchecked across Florida, and there should be great concern about continued spread in this region and their establishment and spread elsewhere.

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DOI: 10.3391/ai.2024.19.2.119829

Authors: Elle K. Sawyer, Jordan H. Hartman, Daniel K. Szydlowski, Eric R. Larson

Abstract: “Sleeper” invaders are non-native populations that experience time-lags post-establishment before subsequent spread or negative impacts, challenging managers to differentiate harmless non-native species from invasive species. In lakes of northern Wisconsin, United States, Rusty Crayfish (Faxonius rusticus Girard, 1852) has dominated as an invasive species for decades, but this species has recently experienced population declines. Following these F. rusticus declines, we rediscovered in 2020 a population of non-native Calico Crayfish (Faxonius immunis Hagen, 1870) that had not been documented since the 1970s. Declining F. rusticus populations may create opportunities for F. immunis spread to other lakes and impacts as a sleeper invader. We conducted additional sampling in summer 2021 that suggests F. immunis remains isolated in only one lake within this watershed. We used mitochondrial DNA barcoding to confirm these crayfish were F. immunis and had not been misidentified as a congener. Next, we investigated whether biotic interactions with F. rusticus may have prevented F. immunis spread over the past several decades. We measured agonistic behaviors using F. immunis and F. rusticus pairs in the laboratory, and then modeled differences in aggression between species while controlling for size and reproductive form. We found that F. rusticus were consistently dominant over F. immunis, suggesting that competition with an established hyper-abundant invasive species may have restricted past spread by F. immunis. Managers and policy makers should consider whether precautionary actions against F. immunis are warranted while the population of this species remains small and localized, especially in the context of F. rusticus declines.

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DOI: 10.3391/ai.2024.19.2.124920

Authors: Nuoxi Wang, Chuyu Luo, Xiaodong Wu, Liang Chen, Xuguang Ge, Cheng Huang, Xiaowen Lin, Shunmei Zhu

Abstract: This study sought to investigate the invasive mechanism of Myriophyllum aquaticum by subjecting it to simulation experiments in varying water temperatures ranging from 0 °C to 30 °C. The results showed that water temperature considerably affected both the growth and reproduction of M. aquaticum. The optimal temperature range for the growth of M. aquaticum was 25‒30 °C. Although the growth of M. aquaticum was inhibited at temperatures between 0‒5 °C, this did not result in mortality. The stem nodes, branches, and diameter reached maximum values over a temperature range of 20‒25 °C. High-temperature stress at 30 °C led to a gradual decrease or disappearance of branches. Compared to the 0 °C, 5 °C, and 30 °C treatment groups, a temperature of 20 °C led to biomass accumulation and significantly higher values. M. aquaticum’s physiological activities were affected by temperature. Except for 10 °C and 15 °C, the catalase activity varied among different water temperatures. M. aquaticum catalase activity was maximal at 5 °C and minimal at 25 °C. Conversely, the synthesis of photosynthetic pigments was highest at 10 °C and 15 °C. The plant’s optimal temperature for growth was between 20 °C and 25 °C. When the temperature was <10 °C, M. aquaticum adapted to the water temperature’s potential damage. This plant has a notable ability to tolerate various temperatures.

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DOI: 10.3391/ai.2024.19.2.117212

Authors: Emanuele Pelella, Flaminia Mariani, Beatrice Questino, Simona Ceschin

Abstract: Freshwater ecosystems are among the most susceptible to biological invasions. The South American Ludwigia hexapetala is an aquatic plant that is becoming an increasing threat in many European waterbodies, recently including Italy. This study aimed to define the main parameters influencing the early colonization stage of L. hexapetala by overlapping the percentage cover of this species with environmental parameter data collected at 24 aquatic sites from six waterbodies in north-central Italy. At each site, chemical and physical characteristics of the water (temperature, pH, dissolved oxygen, conductivity, nitrates, phosphates, ammonia, depth, transparency), grain size of the substrate and level of anthropogenic disturbance were evaluated. The results showed that although L. hexapetala prefers shallow, warm, alkaline, moderately rich in ions and nutrients (especially phosphates) and oxygen-poor waters, it can grow in a wide range of environmental conditions. Moreover, as a typical invasive alien species, it spreads opportunistically in disturbed, unstable sites. Thus, L. hexapetala can invade freshwater habitats with different environmental conditions and subjected to anthropogenic disturbance. However, the results suggest that water depth may be a limiting factor in the early colonization stage of this species, which does not seem to be able to colonise waters deeper than 1 m in investigated sites, while it has been observed in significantly deeper waters in other European countries with a longer invasion history. Detecting the environmental parameters that most influence the growth of L. hexapetala becomes crucial both to identify the sites most at-risk of invasion in which to initiate timely monitoring actions for the species, and to be able to develop better management and control actions for this alien species in sites that have already been invaded.

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DOI: 10.3391/ai.2024.19.1.116273

Authors: Pim Lemmers, Robin Olde Wolbers, Gerard van der Velde, Rob S. E. W. Leuven

Abstract: Co-occurring and morphologically similar species have adapted to differential niches to minimize competition. An invasive alien species can occupy an ‘empty niche’ in introduced ranges. Alternatively, the invader may occupy an overlapping niche and compete with native species to a certain degree. In a Western European lowland brook with high nutrient loads, we studied a benthic community of five fish species, including two alien species: an Asian weatherfish (Misgurnus bipartitus) and the western tubenose goby (Proterorhinus semilunaris). The native species concerned stone loach (Barbatula barbatula), spined loach (Cobitis taenia), and gudgeon (Gobio gobio). Because of the unknown effects of the invaders on native benthic fish species, the trophic position, isotopic niche overlap, and potential food competition among these species were identified using nitrogen and carbon stable isotopes. The trophic levels of the five fish species indicated that they are secondary consumers. The body size of native fish species correlated significantly negatively with their δ15N (‰) signature, in contrast with the invaders indicating that the latter are generalists. Significant isotopic niche overlap was observed among all benthic species. The degree of niche overlap of M. bipartitus was the highest with G. gobio (91.8%). Proterorhinus semilunaris showed the highest degree of niche overlap with B. barbatula (91.2%). It was notable that the observed niche overlap between the native B. barbatula and C. taenia was high (99.2%). Overlap between M. bipartitus and P. semilunaris was low (8.9%), indicating little resource competition between these alien species. Native species showed wider isotopic niches than the invaders. Bayesian mixing models revealed that native and alien species slightly differ in their main diet. The results suggest that the invaders are plastic in their resource use, leading to niche differentiation and promoting the co-existence of benthic fish species.

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DOI: 10.3391/ai.2024.19.1.117155

Authors: Uhram Song, Seok Hyeon Oh, Byoung Woo Kim, Seonah Jeong, Hojun Rim

Abstract: Freshwater ecosystems are vulnerable to the invasion of exotic aquatic plant species because of the great likelihood of the introduction of exotic species, and the lack of barriers that block introduced species. Water hyacinth, Pontederia crassipes Mart., is one of the world’s most invasive alien plant species damaging freshwater ecosystems worldwide. Here, we monitored the water hyacinth population on Jeju island, Korea, to assess current invasion risks. Furthermore, we investigated how water hyacinth affects water pH because pH is an important determinant of the distribution of other aquatic plants, and thus a good indicator of aquatic ecosystem health. Water containing water hyacinth had a pH of 5.3, while that with water hyacinth and soil had a pH of 4.8 72 hours after the start of the experiment. Water hyacinth extracts contained shikimic acid, stearic acid, and palmitic acid, which are possible compounds that caused a decline in water pH. Water hyacinth also inhibited the growth of the aquatic plant species, Spirodela polyrhiza and Lemna perpusilla. These results imply that invasion of water hyacinth adversely impacts the abiotic and biotic characteristics of aquatic ecosystems. Moreover, monitoring the water hyacinth population suggests that this invasive aquatic plant overwinters on Jeju island. Therefore, regular monitoring and subsequent control of water hyacinth population can prevent its expansion in the aquatic habitats of Jeju island and the southern region of the Korean peninsula.

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DOI: 10.3391/ai.2023.18.4.112766

Authors: Quenton M. Tuckett, Timothy J. Lyons, Jeffrey E. Hill

Abstract: Pet abandonment is an important introduction vector for freshwater aquarium fishes, as unwanted pets become too large for tank dimensions and are released into the environment. Concerns over pet abandonment may be particularly important for the U.S. state of Florida, which exhibits abundant access to freshwater habitats and a climate more favorable to tropical aquarium fishes than other continental U.S. states. Numerous studies have examined the factors affecting establishment for non-native species, including the importance of propagule pressure and climate suitability. For freshwater aquarium species, maximum body size can increase pet abandonment because they grow too large for the tank dimensions (i.e., “tankbusters”). Thus, large maximum body size may increase propagule pressure due to intentional release. In addition to being introduced in sufficient numbers, a match between the thermal tolerance of a species and the thermal habitat is necessary for establishment. Several large-bodied catfishes are found in the aquarium trade, including the goonch Bagarius spp., redtail catfish Phractocephalus hemioliopterus, and tiger sorubim Pseudoplatystoma tigrinum. Here, we experimentally determined the chronic lethal minimum temperature (CLmin) for the three catfishes. CLMin estimates for these three species were higher than many other ornamental species, highest for the redtail catfish (14.3 °C), lower for the tiger sorubim (11.0 °C), and lowest (9.9 °C) for the goonch. Given these lethal temperatures, the distribution of redtail catfish would be limited to South Florida while the tiger sorubim and goonch could live, provided other habitat characteristics are suitable, up to ~28°N Latitude in Florida.

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DOI: 10.3391/ai.2023.18.4.111650

Authors: Oscar Flynn, Dan Minchin, Martina B. Caplice, Kate O’Leary, Heather Swanwick, Jan-Robert Baars

Abstract: Quagga and zebra mussels of the genus Dreissena are two of the most impactful freshwater invasive alien species that have spread widely across the globe. These species attach to natural and artificial substrates, form dense populations and filter large volumes of water causing ecological and economic damage. Following the quagga mussel’s discovery in the Shannon River system in Ireland, this study assesses its local distribution, population density, relative abundance, and population structure in the interconnected lakes Lough Ree and Lough Derg in order to determine the likely year and location of its introduction. Polymodal length-frequency analysis was used to distinguish between year cohorts and estimate growth rates. The quagga mussel is established widely across both lakes and is settling on a range of artificial surfaces, natural substrates, dead shells, plant material, and other invasive bivalves. High densities of quagga mussels exceeding 20 000 individuals per m2 were present on artificial surfaces in Lough Ree with total dreissenid densities reaching 26 758 per m2. The relative abundance of quagga mussels to zebra mussels on natural substrates is high in Lough Ree (up to 94.7%) and low in Lough Derg (up to 16.8%). Two to four year cohorts were present at all sites, with quagga mussels attaining large shell sizes over 34 mm in length. Growth varied between sites with a maximum estimated yearly growth rate of 16.8 mm. The time and place of the quagga mussel’s initial introduction in Ireland is still uncertain, but its widespread distribution, population structure, and high population density and relative abundance suggest it was first introduced to Lough Ree in 2016 or 2017.

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DOI: 10.3391/ai.2023.18.2.103850

Authors: Daniel Melo Rosa, Angelo Barbosa Monteiro, Lucas Del Bianco Faria, Paulo Santos Pompeu

Abstract: To investigate the influence of non-native aquatic invertebrate species on food web structure, we selected two reservoirs located in the Grande River (upper Paraná River basin, Brazil) with similar fish communities, different age and different taxa introductions history. We quarterly collected fish and benthonic macroinvertebrates samples in the Volta Grande and Funil reservoirs between October 2015 and August 2016. We used conventional methods of diet evaluation to assess the sampled fish and measured the availability of invertebrates (i.e. composition and density) present in the sediment samples from each reservoir. In addition, we performed a structural analysis of trophic interaction networks. Based on the data obtained, it was possible to identify that in Volta Grande most of the energy flow, between benthonic invertebrates (prey) and the fish community (predators), occurred through non-native prey species, especially Limnoperna fortunei and Macrobrachium amazonicum, while in Funil it was shared between non-native and native prey. Species loss simulations indicated that the networks did not differ substantially between random losses and losses between groups. In general, there was a decrease in the probability of occurrence of highly connected species in both reservoirs and between non-native and native species. Results showed that the new interactions among species influenced the importance of the available energy sources for the fish in the Volta Grande reservoir. The presence of non-native prey, especially M. amazonicum, may influence the interaction network structure, promoting community dependence on non-native species to ensure robustness to environmental disturbances. In the absence of pre-invasion data, the comparative study between systems with similar fish communities may provide a better understanding of the impacts caused by the introduction of non-native invertebrate prey.

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DOI: 10.3391/ai.2023.18.2.104203

Authors: Pratyush Jaishanker, Daya Hall-Stratton, Amy E. Fowler

Abstract: The freshwater Japanese mystery snail (Heterogen japonica) was introduced to the United States in the early 1900s and has since established populations throughout the continent. The species has ovoviviparous reproduction (i.e., eggs hatch within the mother and develop inside before being released as juveniles), which is one reason it has been successful. Despite its wide geographic range, little is known about its physiological tolerances. For example, high salinities and temperatures may limit its spread, and determining the species’ tolerance to these environmental factors is crucial to predict its possible range expansion. To test this, 600 juvenile H. japonica (average shell length: 6.0mm, range: 4.5–8.3mm) were collected from 28 females from a lake in Virginia, USA and placed in a fully crossed design to test the interaction between salinity (0.2 and 2 PSU) and temperature (25 °C, 34 °C and 38 °C). Juveniles were monitored for mortality over two weeks. Kaplan–Meier survival analyses determined median survival probabilities, and generalized linear models compared differences in mean survival. All juveniles in 25 °C (except one in 0.2 PSU) survived (N=199/200), and all juveniles in 38 °C died by the end of 14 days (N=200), irrespective of salinity. However, juveniles kept at 38 °C showed higher early (≤4 days) mortality in 0.2 PSU, but lower early mortality in 2 PSU. Importantly, juveniles in 2 PSU survived for ≥2 days (N=294/300) across all temperatures, indicating that there may be scope for expansion through estuaries. Future work should examine temperatures between 34 and 38 °C and salinities above 2 PSU to understand the extent of covariance between salinity and temperature and create mathematical models to estimate survivability and spread.

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DOI: 10.3391/ai.2023.18.2.103208

Authors: James W. E. Dickey, Jonathan M. Jeschke, Gregor T. Steffen, Elžbieta Kazanavičiūtė, Reid S. Brennan, Elizabeta Briski

Abstract: The pet trade has facilitated the spread of invasive alien species (IAS) globally, with negative consequences for biodiversity. The prediction of impacts is a major goal for invasion ecologists, and is especially crucial in an industry often lacking knowledge about traded species. We focused on the predatory gastropod Anentome helena, a species originating in south-east Asia and traded around the world, but with taxonomic uncertainty. We first set out to determine where our study organism fell within the A. “helena” species complex, known to comprise at least four cryptic species, before assessing the effect of temperature on the number of prey, the pulmonate snail Physella acuta, killed per predator via functional response experiments at two temperatures. We used 22 °C as a recommended temperature for housing the species in captivity, and 18 °C as a representative summer lake temperature in temperate climates of Europe. We also assessed the role of predator group size (1×, 2×, 3×) on predation (total consumption and average per capita consumption) at the experimental temperatures with fixed densities of prey, as well as the effect of these temperatures on prey activity. Our organisms belonged to a cryptic species originating from Thailand (Anentome sp. A), matching the findings of aquarium trade samples in other continents. In the functional response experiments, we found maximum feeding rate to be significantly reduced at the lower temperature. A similar result ensued from group feeding, with total consumption significantly reduced and the reduction in average per capita consumption approaching significance at the lower temperature. There was no significant effect of group size on the average per capita consumption in the group trial, indicating neutral conspecific interactions. No significant effect of temperature on the activity of the prey species was found, suggesting decreased consumption was mainly driven by predator, rather than prey. These results suggest limited A. helena impacts in the short-term, but increasing temperatures with climate change may facilitate greater consequences from releases. We suggest future studies assess other potential predatory impacts and survival across relevant abiotic conditions, and encourage the use of similar methods to assess the impacts of other commonly traded species.

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DOI: 10.3391/ai.2023.18.2.105436

Authors: Nicolas Trunfio, Thibaut Bournonville, Nicolas Debortoli, Jonathan Marescaux, Géraldine Nogaro, Jean-Nicolas Beisel

Abstract: The quagga mussel (Dreissena rostriformis bugensis) was first recorded in France in the Moselle River in 2011. The objective of this study was to obtain a better understanding of the species’ demographic and genetic structure ten years after its first observation. To do this, we examined quagga mussel (i) relative abundance/biomass (compared with the zebra mussel (Dreissena polymorpha), (ii) population structure, and (iii) genetic structure along the navigable stretch of the Moselle during four sampling events conducted between May 2021 and May 2022. The results indicate that, while zebra mussels are still the dominant species (ca. 2/3 of all dreissenid species), quagga mussels represent, on average, 60% of dreissenid biomass. A typical quagga population was composed of five different cohorts with wide, overlapping size ranges, suggesting that the mussels breed for much of the year. Growth in quagga mussel shell length was at least 1.4× greater than that for zebra mussels, regardless of season, with no interruption in growth observed during winter. Unlike zebra mussels, we failed to record any small quagga individuals (4–14 mm shell length) in our samples, possibly indicating high mortality induced by selective predation by invasive round gobies Neogobius melanostomus. Genetically, the three Moselle quagga mussel populations examined were highly homogeneous among themselves (based on microsatellite analysis), and very similar to those found elsewhere in Europe (diversity of CO1 haplotypes). A comparison with previous data suggests that the Moselle quagga population comprises haplotypes introduced over several successive introduction waves, a process that may continue in the future.

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DOI: 10.3391/ai.2023.18.2.105548

Authors: Christine Ewers, Monika Normant-Saremba, Heleen Keirsebelik, Jonas Schoelynck

Abstract: The geographic expansion and abundance fluctuations of invasive species offer unprecedented insights to investigate potential mechanisms underlying the distribution-abundance relationship, one of the most universal patterns in community ecology. However, the abundance of invasive species is rarely documented in the needed detail. Data from historical records, scientific and popular literature, citizen science and expert interviews were synthesized to obtain insights into the long-term expansion and abundance cycles of the Chinese mitten crab, one of the world’s 100 worst invasive species. Thus for the first time, global long-term data on population size fluctuations have been correlated with the global spatiotemporal invasion history of a non-native species. Geographic expansions and increases in abundance co-occurred in the 1930s and again since the 1990s in agreement with the distribution-abundance relationship. Furthermore, a regional case study for the German river Elbe indicates that increases in abundance may be driven by improved riverine water quality and rising sea surface temperatures. Environmental restoration and climate change therefore benefit this invasive species, and could lead to further geographic expansion and increases in abundance.

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DOI: 10.3391/ai.2023.18.2.108485

Authors: Hugo Verreycken, Frank P. L. Collas, Neil E. Coughlan

Abstract: The 22nd International Conference on Aquatic Invasive Species (ICAIS) was held as a hybrid event in Oostende, Belgium from 18–22 April 2022. The conference addressed the theme of “Global Climate Change Amplifies Aquatic Invasive Species Impacts” and aimed to expand knowledge on the latest science and policy, inspire cooperation and collaboration on research and management projects at a global scale. Seven renowned international scientists provided keynote presentations on perspectives of climate change within their respective areas of expertise. This special issue of Aquatic Invasions presents nine academic papers addressing a range of aquatic invasive species issues including predation, life history dynamics, ecosystem impacts, and physiological tolerances. The papers highlight the need for regional, national, and international cooperation, collaboration on research and management projects, and targeted, specific, and actionable outreach to combat the growing threat posed by aquatic invasive species.

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DOI: 10.3391/ai.2023.18.1.103610

Authors: Wen Xiong, Dong Xie, Qiang Wang, Hui Wang, Zhigang Wu, Heying Sun, Tao Li, Peter A. Bowler

Abstract: Poyang Lake is the largest freshwater lake in China and sustains a high level of biodiversity in the mid-reach area of the Yangtze River watershed. Poyang Lake is also one of the most important aquaculture regions in China, and a great number of non-native species have been introduced into it. We present a current and well-documented list of the non-native species of plants, molluscs, crustaceans, fishes, reptiles, and amphibians currently found in Lake. We found that there are 103 non-native species (83 vascular plants, 12 fishes, three crustacea, two molluscs, two reptiles and one amphibian) that have invaded Poyang Lake Basin, of which 96 non-native species were introduced after 2000. The invasion rate of non-native species reached 4.36 species year-1, which is the highest invasion rate recorded in freshwater ecosystems. The primary pathways of introduction are through the ornamental trade and unintentional escapes (30 species each, respectively), followed by food (19), aquaculture (15), forage grass (four), medicinal and oil (two, respectively), and biocontrol (one). The origins of non-native species are North America (29.12%), Asia (25.24%), South America (20.38%), Africa (18.44%), Europe (5.82%) and Oceania (0.97%). Many non-native species provide significant support for the rapid development of the local economy (such as aquaculture). However, many non-native species pose a great threat to local biodiversity and societal development. More studies that include monitoring and the development of strategies for managing and eliminating non-native species in Poyang Lake are needed.

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DOI: 10.3391/ai.2023.18.1.103389

Authors: Michele D. Larson, Daniel Greenwood, Kara Flanigan, Amy C. Krist

Abstract: Environmental conditions promoting the occurrence and high abundance of non-native taxa are linked to critical stages of species invasions: establishment, whether a site can sustain a population of the non-native taxon, and impact, the extent to which the consequences of establishment negatively affect the invaded ecosystem. Using surveys across environmental gradients, we examined the physicochemical conditions associated with the occurrence and abundance of the invasive New Zealand mudsnail (Potamopyrgus antipodarum) and co-occurring native mollusks. Abundance of Potamopyrgus very strongly increased with stream width and conductivity (specifically with chloride, sulfate, potassium, and sodium ions). Also, Potamopyrgus were most likely to occur at sites with relatively low pH and water velocity and relatively high calcium ion concentration and abundance also slightly increased in these conditions. The physicochemical conditions indicate the characteristics of sites that are suitable for establishment and secondary spread of Potamopyrgus. Native mollusks differed from Potamopyrgus in the physicochemical conditions associated with abundance suggesting that variation among habitats could permit native mollusks to persist at larger geographic scales even if they often co-occur with Potamopyrgus. Abundance of native Physa moderately decreased with abundance of Potamopyrgus. Because abundance of Physa and Potamopyrgus responded oppositely to stream width and conductivity, the negative relationship between the abundance of these two taxa may be caused by contrasting responses to physicochemical conditions, acting alone or in concert with biotic interactions.

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