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.
Calyptospadix cerulea Clarke, 1882 is a colonial athecate hydrozoan known for forming dense biofouling communities, having broad environmental tolerance and global yet taxonomically obscured distribution. Here, we confirm for the first time its presence in the Polish part of the Baltic Sea (Gulf of Gdańsk), marking a significant range expansion into the Baltic Proper. We support our morphology-based identification, with the first molecular data for C. cerulea, allowing its phylogenetic placement within a clade alongside Bimeria vestita Wright, 1859 and Cordylophora caspia (Pallas, 1771), therefore suggesting reassignment to the family Cordylophoridae. We also reviewed historical occurrence data of C. cerulea, spanning nearly 150 years of research, to provide up-to-date description of its distribution range. In addition, our in situ observations suggest that C. cerulea plays an important role in providing secondary substrate for number of species in benthic environments of the southern Baltic Sea. As C. cerulea is likely well-suited to the Baltic’s variable brackish conditions, its presence raises concerns about potential ecological impacts on native fouling communities and industrial infrastructure. Given its ecological plasticity and expanding range, we emphasize the need for continued monitoring and further research into its population dynamics, ecological interactions, and potential impacts.
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.
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.
The Atlantic blue crab (Callinectes sapidus) is among the 100 worst invasive species in the Mediterranean Sea, causing significant ecological and economic impacts. The aim of this study is to investigate key aspects of the species’ biology and ecology during its demographic outbreak in a Northern Adriatic area significantly affected by the species’ invasion. Year-round sampling was carried out across a short spatial gradient encompassing lagoon, estuarine, and marine habitats. This comprehensive approach aimed to elucidate the invasive success of the blue crab. Our findings shows that the species resulted widely distributed across all habitat types, with significant differences among stations, seasons, and sexes, with females being prevalent in higher salinity marine and outer lagoon waters during spawning season. These findings, along with the spatiotemporal analyses of the condition factor and the presence in the lagoon of various cohorts of juveniles over the year, highlight the completion of the complex life cycle of the blue crab on an extremely small spatial scale. Moreover, with an average of over 2 million eggs laid per female and a prolonged spawning season, the species reveals a robust reproductive potential, likely favoured by the short distance between mating and spawning habitats. In conclusion, the results of this study underscore the critical role of the short spatial environmental mosaic in facilitating the invasive success of C. sapidus, providing relevant data for managing this unprecedented demographic explosion.
The aquatic plant Myriophyllum aquaticum, native to South America, has been introduced to China as an aquarium ornamental plant species over the past 20 years and has now established itself as an invasive species in multiple regions of southern China. In the present study, we conducted a controlled pot experiment with Myriophyllum aquaticum planted at seven different water depths (0, 25, 50, 75, 100, 125, and 150 cm) to investigate its growth patterns and adaptive mechanisms in various aquatic environments. As expected, underwater light decreased exponentially with increasing water depth. Spectral analysis indicated significant attenuation across all wavelength bands, with the blue light band being reduced to a greater extent than the red light band, consequently leading to a gradual elevation in the red-to-blue ratio (Red/Blue) with depth, which has a significant effect on the survival rate of M. aquaticum. With an increase in water depth, the survival rate of M. aquaticum showed a decreasing trend; the plants did not survive at a depth of 150 cm. The effect of water depth on the growth and reproduction of M. aquaticum is evident. The growth indices, namely plant height, the number of stem nodes, internodes, the number of branches, the number of tillers, root length, wet weight, and the RGR were all shown to decrease with increasing water depth. Growth conditions gradually diminished with the increase in depth: the Chl-a content of the M. aquaticum leaves gradually decreased, and when the water depth was ≥ 50 cm, the chlorophyll synthesizing ability of the leaves gradually decreased. Increased water depth – and the corresponding stress of low light – resulted in an increase in the malondialdehyde content of the leaves. The results of this experiment demonstrate that M. aquaticum is more likely to become established in shallow-water areas (depth up to 25 cm).
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.
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.
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.
The African clawed frog Xenopus laevis is invasive on four continents, and is recognized as one of the invasive amphibians that generates the greatest impacts in the ecosystems it invades. Although its diet has been studied in its native habitat and invaded areas, its trophic role is still unclear, especially in the communities it invades. We studied the diet of X. laevis, and looked at its stable isotope signatures and its bioaccumulation of heavy metals, to gain a better understanding of its trophic role. The diet was found to consist mainly of aquatic invertebrates, with some consumption of the native fish Cheirodon pisciculus. The isotope analysis revealed that the assimilation of prey by X. laevis is unrelated to the most-consumed item. Xenopus laevis occupied a high trophic position in its own stream and was segregated from fish in by its use of trophic resources. Despite its high trophic position, only biomagnification of copper and zinc was found in relation to some prey, but not manganese or arsenic.
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.
This study documents the first occurrence and rapid expansion of the solitary ascidian Cnemidocarpa irene in natural marine habitats of Tenerife (Canary Islands). Native to the Indo-Pacific, C. irene had previously been introduced to the Caribbean, Brazil, and Cape Verde. It was first observed in Tenerife in 2020, though retrospective records through citizen science tools date its presence back to 2018. A total of 74 sightings along the island’s coasts were reported between 2018 and 2024, when it reached densities of ca. 2 individuals/aggregates per square metre in the initial introduction area. Thus, the species is undergoing a clear proliferation and a spatial expansion. Morphological and genetic analyses confirmed the identity of C. irene and its phylogenetic placement, closely related to other Cnemidocarpa and related genera such as Asterocarpa. This species shows concerning invasive characteristics, such as a fast expansion, abundance in natural habitats, and aggregative behaviour, suggesting potential threats to native biota. Due to its limited natural dispersal capacity, the introduction of C. irene to Tenerife is attributed to anthropogenic vectors, particularly oil platforms arriving at major Canary Island ports. The proximity of the initial records to port areas supports this hypothesis. Given the potential species’ ecological risks, the authors recommend close monitoring, manual removal where feasible, and strengthened involvement of citizen science. This case highlights the vulnerability of oceanic islands to marine biological invasions and the importance of ports and marinas as critical entry points, underscoring the need for proactive surveillance and early intervention strategies.
Arcuatula senhousia is a non-indigenous species first observed in Arcachon Bay in 2002. At that time, the species’ distribution was restricted to the northern part of this coastal lagoon. During the following 7–8 years, the species also started to colonise its south-eastern parts. Then, two surveys conducted in 2018 and 2021 showed that the species was observed over most of the investigated tidal flats within the lagoon. Between those two periods, there was a threefold increase in both frequencies of occurrence and average densities. The highest average densities and frequencies were observed in areas colonised in 2002. It suggests that this area is either the main area of introduction/settlement for the species or the area where it could find the most suitable ecological conditions. However, the use of Species Distribution Modelling showed that, considering habitat features, most of the intertidal flats in Arcachon Bay were a highly suitable habitat for A. senhousia. Further colonisation of the lagoon during the coming years appears very likely. The study of its habitat in this area suggested that the presence of meadows favoured the settlement of A. senhousia individuals. Furthermore, lower bottom current velocity and the erosion potential it induces seemed to be the principal environmental factors driving the distribution pattern of this species within the bay. However, other factors that could regulate the spread of A. senhousia must be considered. Understanding the dynamics of A. senhousia colonisation and identifying its drivers aimed to characterise possible areas to be colonised by this species. This is a crucial point in determining how to manage its distribution and assess the risk of spreading within other ecosystems.
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.
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.
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.
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.
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.
Aquatic invasive species can alter ecosystem processes, detrimentally affect native species, and facilitate the invasion of other species. One infamous aquatic invader, the zebra mussel (Dreissena polymorpha), is known to cause declines in phytoplankton through their filtering activity and facilitate the subsequent growth of macrophytes by increasing water clarity. In turn, submerged macrophytes may provide substrate for settlement of zebra mussels. The goal of this study was to examine variation in the distribution of zebra mussels and hydrilla (Hydrilla verticillata subsp. verticillata) in relation to sediment composition, each other (including potential facilitation), and with season (summer vs. fall) in a subtropical reservoir. Surveys of zebra mussels and hydrilla showed that zebra mussel densities tended to be higher in rocky habitats where they were found on hydrilla and rocks (gravel and cobble), compared to muddy habitats where they were found only on hydrilla. Within the rocky habitat, zebra mussels attached to hydrilla had significantly higher densities and a smaller size than those attached to rocks. However, spring populations may be largely transient because only a small fraction of zebra mussels remained on hydrilla in early fall, almost exclusively representing a new settlement cohort based on their size distribution. Nevertheless, hydrilla may directly facilitate zebra mussel dispersal, especially in spring, as mussels attached to plant fragments can be transported downstream by currents or by human activities, such as entanglement in boat propellers and trailers. Laboratory experiments did not detect any significant impact of zebra mussels on the growth, biomass, or nutrient content of hydrilla. However, zebra mussel biomass was higher when hydrilla was present, suggesting that hydrilla may facilitate zebra mussel growth, although the difference was only statistically significant at low hydrilla densities. This study illustrates the complexities of interactions between multiple introduced species which can lead to facilitation of invasion of aquatic ecosystems.
Understanding the long-term trends of biological invasions and their drivers is a pivotal issue. However, it is challenging because collecting presence/abundance data of invasive species as well as environmental/biotic factors over a period of years is time-consuming and therefore such data is scarce compared to short-term studies. Here, we investigated whether environmental and biotic factors in highly regulated eutrophic marshlands (water regime, physico-chemistry, habitat features, and predatory fish biomass) successfully accounted for spatiotemporal trends in abundance of small and large red swamp crayfish (Procambarus clarkii) in drainage ditches over seven consecutive years. For this, we used length-frequency data collected during the annual peak in crayfish activity. We also explored whether variation in crayfish abundance over time was due to density-dependent effects (temporal autocorrelation). We found large variation in crayfish abundance expressed in capture per unit effort (CPUE) between ditches and for different years (by a factor of 10 and 6 for small and large individuals) but with no specific trend over time. No density-dependent effect was found in any of the ditches. While crayfish CPUE was poorly related to the water regime (in particular dryness intensity of ditches for small crayfish), it was favoured by densely vegetated banks and negatively linked to the density of surrounding ditches for the two life stages. No relationship was detected with predatory fish biomass or any of the other environmental factors studied. Controlling crayfish abundance by managing environmental conditions seems possible in some cases, but likely costly for other components of biodiversity. Trapping could be a possible strategy when populations dropped to low densities in places. Finally, further studies are needed in ecosystems covering a wider range of environmental conditions to provide a more comprehensive understanding of the long-term trend of the species.
