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.2026.21.2.188183

Authors: Marta Ronowicz, Bernabé Moreno, Zuzanna Szewel, Julia Więcławska, Olga Brocławik, Maciej Karol Mańko

Abstract: 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.

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DOI: 10.3391/ai.2026.21.1.180751

Authors: Marco Boschiero, Chiara Facca, Francesco Cavraro, Simone Redolfi Bristol, Anna Gavioli, Federico Riccato, Matteo Zucchetta, Piero Franzoi

Abstract: 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.

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DOI: 10.3391/ai.2025.20.4.166447

Authors: Salomé Coignard, Marie Fouet, Hugues Blanchet, Cécile Massé, Nathalie Caill-Milly, Florence Sanchez, Muriel Lissardy, Florian Ganthy, Guillaume Bernard

Abstract: 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.

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DOI: 10.3391/ai.2025.20.3.153547

Authors: André Mauchamp, Anne Bonis, Julie Crabot, Benjamin Bergerot, Olivier Gore, Jean-Marc Paillisson

Abstract: 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.

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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.2025.20.2.154614

Authors: Yuriy Kvach, Halyna Gabrielczak, Anastasiia Lepekha, Mikhail O. Son, Sergii Khutornoi

Abstract: Biological invasions pose a significant threat to aquatic ecosystems, and the spread of uncontrolled non-indigenous species can have detrimental effects on biodiversity, ecosystem processes, and economic activities. The Chesapeake blue crab, Callinectes sapidus, native to the western Atlantic Ocean, is non-indigenous in the Black Sea region. This study presents novel findings on its presence and breeding in the Black Sea, particularly in North-Western part within the territorial confines of Ukraine. The study provides evidence of successful reproduction by a female blue crab with eggs in this non-native habitat, i.e. off the coast of Ukraine. Furthermore, molecular DNA barcoding analysis revealed the Ukrainian crab to be of a haplotype found in Italy and the United States, indicating potential connectivity between the Black Sea population and other established populations. Additionally, other haplotypes were detected in the Black Sea region, suggesting the possibility of multiple introductions and admixture between non-indigenous populations of different origins. The successful establishment and spread of C. sapidus in the Black Sea region may be attributed to its adaptability to a wide range of environmental conditions and the lack of natural predators or competitors in the invaded regions. This crab is commercialized in the USA, which may have implications for fisheries and aquaculture activities in Ukraine.

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DOI: 10.3391/ai.2025.20.1.154604

Authors: Amy E. Fowler, Alejandro Bortolus, João Canning-Clode, Tamara B. Robinson, Thomas W. Therriault

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

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DOI: 10.3391/ai.2024.19.4.136332

Authors: Natalia Z. Szydłowska, Marek Let, Pavel Franta, Miloš Buřič, Susanne Worischka, Luise Richter, Bořek Drozd

Abstract: The round goby (Neogobius melanostomus) is a well-known invasive fish. Knowledge of its feeding habits and means of food processing is key in understanding its impact on aquatic food webs. The present study assessed the gut evacuation rate of round gobies feeding on three different types of prey occurring naturally in the diet of this species (small native freshwater clams, an invasive amphipod and chironomid larvae), at two different temperatures (14 and 20 °C) and under different food availability scenarios (continuous and non-continuous feeding). Gut evacuation rates varied significantly between the prey availability scenarios and, specifically, round gobies processed prey significantly faster in the continuous feeding mode when food was regularly available than when fed only once. The highest evacuation rates were detected for individuals fed with clams, in which complete gut clearance was observed within 16 h, compared to within 24 h and 36 h for chironomid larvae and amphipods, respectively. Our study shows that round gobies evacuate chironomid and mollusc prey most rapidly, which suggests that potentially the highest predatory pressure will be exerted on these prey types, assuming that all three prey species are locally present. The slower processing and digestion of amphipods may be due to their bulkier shape, which makes them more difficult to swallow. The relatively high evacuation efficiency of the round goby observed in the continuous feeding mode suggests overall increased pressure on food resources, thereby potentially reducing availability for other consumers and accelerating resource depletion, mainly driven by the high local densities of the round goby populations.

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DOI: 10.3391/ai.2024.19.4.141425

Authors: Karl J. Wittmann, Ton van Haaren, Rianna Vlierboom

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

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DOI: 10.3391/ai.2024.19.4.141952

Authors: Marcos R. R. Dias, João L. T. Pestana, Ana L. Machado

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

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DOI: 10.3391/ai.2024.19.135332

Authors: Carmen M. Sierra Lemus, Angela Schmitz Ornés, Martin Haase

Abstract: The dependence of freshwater snails on the availability of ions through their ambient water varies widely across species and deficiencies may limit reproduction and other physiological functions. Nevertheless, in many studies on the New Zealand mud snail (NZMS) Potamopyrgus antipodarum, where reactions on components dissolved in the water are not the focus, the composition of the water the snails are kept in is not specified. We tested the sensitivity of reproduction to three types of artificial fresh water in three parthenogenetic lineages invasive to Europe. The three lineages descended each from a single mother collected in the same population in northern Germany. Reproduction was measured as the number of offspring sired within 12 weeks and varied across water types, however, lineages differed in their reaction norms. This indicates 1) that reproduction of the NZMS is indeed sensitive to the composition of the water and 2) that there is fitness relevant genetic variation which probably has arisen only within the 160–180 years the NZMS is present in Europe, i.e. we witness clonal evolution. For experiments, this means that the water composition should not be neglected and that potential genetic variation even among closely related clonal lineages has to be accounted for in order to ensure comparability and reproducibility.

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DOI: 10.3391/ai.2024.19.3.134464

Authors: Carlotta Meriggi, Richard K. Johnson, Ane T. Laugen, Stina Drakare

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

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DOI: 10.3391/ai.2024.19.2.124566

Authors: Marinus van der Gaag, Gerard van der Velde, Rob S. E. W. Leuven

Abstract: The invasive alien false mussels Mytilopsis leucophaeata cochleata and Dreissena polymorpha (Dreissenidae) have established populations in the North Sea canal in the Netherlands that connects the harbours of Amsterdam with the North Sea. The favourable and unfavourable salinity ranges of both species were earlier studied in long-term outdoor mesocosm experiments. Their occurrence in salinity gradients in estuaries or canals connecting seaways to freshwater harbours provides information on their salinity tolerance under field conditions. By the combination of laboratory experiments and field data using the same source population a high predictability can be expected for establishment of the gradients facilitated by constructions. The reliability of experimentally derived salinity-tolerance limits for both dreissenid species was tested using data on their distribution in a salinity gradient of the littoral zone along the North Sea canal. The mussels used for the survival experiments in mesocosms were also collected from this canal. Favourable salinity ranges for adult survival in the mesocosms were 0.2 – 17.5 for M. leucophaeata cochleata and 0.2 – 6.0 for D. polymorpha. Unfavourable salinities were outside these ranges and led to high and fast mortality of these species. Mytilopsis leucophaeata cochleata was present over nearly the whole length of the North Sea canal with the highest densities close to the sea sluices where also the highest salinities and water temperatures were measured. Their densities in the canal decreased gradually at larger distances from the sea. Dreissena polymorpha co-exists with M. leucophaeata cochleata at the east end of the canal with low salinity due to the influence of freshwater of the river Rhine. The occurrence of D. polymorpha was restricted to a salinity below 4 and M. leucophaeata cochleata only occurred at a salinity above 1.5 (maximum value measured in the canal 9.2). Shorter salinity gradients with lower salinity ranges provided additional information on the co-existence of both species. Co-existence was observed at a salinity range of 1.5–3.3 (own data), 1.0–3.5 (Van Couwelaar and Van Dijk 1989), both in the North Sea canal, and 0.2–2.8, in the Canal through Voorne (Janssen and Janssen-Kruit 1967). These data correspond with studies of both species by Walton (1996) in the Hudson River (salinity range 0–3). Found salinity ranges in the North Sea canal for both species match with the tolerance results obtained by mesocosm experiments. A new invading dreissenid mussel Dreissena rostriformis bugensis and a mytilid Ischadium recurvum occur in the North Sea canal since 2006 and 2012, respectively. Competition between recent and earlier invaders is likely when salinity tolerances are similar. It has already been observed that D. rostriformis bugensis outcompetes D. polymorpha under freshwater conditions (Bij de Vaate et al. 2014; Matthews et al. 2014). Ischadium recurvum has the potential to colonize large parts of the canal and to be a strong competitor of M. leucophaeata cochleata (Goud et al. 2019). Since January 2022, the new ‘Zeesluis IJmuiden’ with the biggest locks in the world is in use, affecting the probability of population establishment of new introduced and invasive alien mussel species.

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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.2024.19.1.114856

Authors: Knut Mehler, Anna M. Labecka, Ioan Sîrbu, Natasha Y. Flores, Rob S. E. W. Leuven, Frank P. L. Collas

Abstract: The alien freshwater mussel Sinanodonta woodiana (Lea, 1834) has rapidly spread throughout Europe over the past decades. This species can cope with a broad range of environmental conditions and has a high reproductive capacity making S. woodiana a successful invader. Due to its negative effects on native freshwater mollusk communities and parasitized fish it is critical to identify suitable habitats where S. woodiana may persist and how these habitats may be altered under future climate projections. We applied multivariate ordination methods to analyze the space-time relationship and a maximum entropy approach (MaxEnt) to predict the recent (1970–2000) and future (2041–2060 and 2081–2100) distribution of S. woodiana using environmental and climate variables for the European continent. After first sightings in 1979 there were only a few new locations and findings which increased unevenly and exponentially to a maximum of about 100 new locations per year followed by decline during the last few years. Under recent climate condition, 2.3% of European watersheds are predicted as highly suitable habitat for S. woodiana and located in the temperate climate zone between 40°N and 60°N. Suitable habitat was associated with lowland watersheds characterized by fluviatile deposits and agriculture. Elevation, the distance between water bodies, land cover and mean temperature of the coldest quarter were the main factors influencing the modeling results. For future climate scenarios, highly suitable habitat increased to 2.4% by the middle of this century and decreased to 2.2% by the end of the century under the ‘least radiative forcing’ scenario. For the intermediate and high radiative forcing in 2050 and 2100, highly suitable habitat decreased to 2.2% and 1.7% and to 2.2% and 2.2%, respectively. Results from our study can be used as a baseline to better understand potential invasion pathways, identify high risk areas, and to initiate early detection and rapid response strategies.

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DOI: 10.3391/ai.2023.18.4.113911

Authors: Pavel Franta, Radek Gebauer, Lukáš Veselý, Natalia Z. Szydłowska, Bořek Drozd

Abstract: Abundance and per-capita foraging efficiency are essential factors for predicting and quantifying an invasive predator impact on prey, i.e., the impact potential (IP). However, population structure is not included in the calculation, and IP accuracy might be improved by incorporating predator body size. The population structure of the round goby Neogobius melanostomus, a highly invasive predator, was surveyed in the Elbe River. We determined the functional response (FR, per capita foraging) of the three most abundant size classes of N. melanostomus on the water louse Asellus aquaticus. We then calculated the IP for each size class and for the entire population with (the actual impact potential – IPA) and without (the impact potential for limit size rage – IPLSR) population body size structure (based on FR of the medium size class). All three size classes of the predator showed type II FR with respect to A. aquaticus. The estimated FR parameters, attack rate and handling time, as well as the maximum feeding rate, were size dependent. Despite the lowest per capita foraging efficiency, small individuals displayed the highest IP among the tested size classes because of their high abundance. Conversely, medium and large individuals, although showing highest per capita foraging efficiency, displayed lower IP. Hence, IPA showed more precise IP calculations compared to IPLSR. Overestimation of the potential impact as a consequence of omitting predator population size structure was negligible at the investigated locality. The IP of the N. melanostomus population five years post-invasion can be accurately calculated based on the FR of medium-sized fish.

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DOI: 10.3391/ai.2023.18.4.113092

Authors: Anna Stępień, Anna M. Jażdżewska, Romeu S. Ribeiro, Rafael Santos, Macarena Ros

Abstract: A major challenge in invasion science is detecting overlooked introductions, their pathways of introduction and spread. One of the most successful introduced taxa in aquatic ecosystems are peracarid crustaceans. There are a growing number of reports of accidental introductions of peracarids worldwide, mostly related to human transport hubs (e.g., ports and marinas). Tanaidaceans are especially abundant in these communities. Most frequently given examples of natural and anthropogenic passive dispersers belong to the family Tanaididae. However, their wide distribution requires confirmation. Most records come from 70–80’ of last century, when identification of the species relied only on morphological characters. The small size and large intraspecific variation of tanaidids generate a high taxonomic uncertainty, as in the case of Zeuxo turkensis. Population of this species was previously known from Turkish, Japanese, and Australian coasts. In the two last places this tanaidid was identified as Hexapleomera sasuke, despite there were some premises that it should be synonymized with Z. turkensis. Here we investigate specimens that resembled both Hexapleomera sasuke and Zeuxo turkensis collected in marinas around the Iberian and Moroccan coasts. Integrating morphological and molecular methods (barcoding) we confirmed: (1) the first record and presence of well-structured populations of Z. turkensis in Spain, Portugal and Morocco, representing the first record of the species for Atlantic waters; (2) the conspecificity between H. sasuke and Z. turkensis, which should be synonymized; and (3) the wide distribution of Z. turkensis associated with human transport hubs (i.e. marinas) in the study area, showing its potential for introduction and spread. Integrated approaches and greater taxonomic support are key to advancing knowledge on the origin and invasion patterns of this and other small and poorly known human-mediated widespread species.

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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.2023.18.3.109673

Authors: Przemysław Czerniejewski, Jarosław Dąbrowski, Adam Brysiewicz, Krzysztof Formicki

Abstract: The native North American bivalve species Rangia cuneata was unintentionally introduced into European waters during the first decade of the 21st century. In the Baltic Sea, it is mostly found along the southeastern coast, but in 2018 researchers also discovered the species in the Bay of Pomerania, which indicated that it could eventually inhabit the adjacent Szczecin Lagoon and Odra River. In 2021, the species was discovered for the first time in the Szczecin Lagoon during a sampling campaign, at 5 out of the 12 dispersed study sites with diverse bottom substrates. The goal of this study was to ascertain R. cuneata population density, morphometric parameters, individual growth, and the potential for further expansion in the southern Baltic Sea waters. For the study, 201 individuals of this species were collected. Compared to other sites in the southeast Baltic, the Szczecin Lagoon had a much lower average R. cuneata population density, at 13.2 ± 7.11 individuals m-2 of the bottom area. The highest population density was found at sites with more silt (4–63 µm) and less sand (>63 µm). R. cuneata shells had an average length of 30.9 ± 4.6 mm and an average weight of 6.6 ± 2.8 g. The collected specimens were greater in size than other populations of the species in the Baltic Sea and were comparable in size to populations from the nearby Bay of Pomerania. There were no specimens that were under 10 mm in length, and the population was dominated by specimens in the 25–30 mm and 30–35 mm ranges, as well as the 3+ and 4+ age groups. Given the R. cuneata’s invasive potential and its fast rate of colonization of new areas, it would be prudent to monitor this population and the species migration patterns across the estuary waters of the western Baltic.

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DOI: 10.3391/ai.2023.18.3.106635

Authors: Jean-Charles Pavard, Vincent M. P. Bouchet, Julien Richirt, Apolyne Courleux, Eric Armynot du Châtelet, Gwendoline Duong, Romain Abraham, Jean-Philippe Pezy, Jean-Claude Dauvin, Laurent Seuront

Abstract: Though the morphological discrimination of the three pseudo-cryptic Ammonia species, A. aberdoveyensis, A. confertitesta and A. veneta, has been recently established, information on their ecology and habitats are still relatively scarce. This study aims to define distribution patterns of these species at eight sites scattered along the French coasts of the English Channel, over a total of 39 stations. These sites were classified into two habitats, either harbours (heavily modified sites) or less impacted (moderately influenced sites). The use of IndVal index (an index based on how a species is statistically specific to a habitat) clearly indicates that A. confertitesta is recorded preferentially in or close to harbours. Considering its non-indigenous species (NIS) status in Europe, we investigated its reported occurrences in Europe in the literature. It almost always showed a proximity to major European harbours. Sometimes, this species occurred relatively far away from these harbours, suggesting a secondary spread. Finally, this work interprets A. confertitesta being a NIS in the eastern English Channel with assumptions of being invasive regarding its dominance over the indigenous species A. aberdoveyensis and A. veneta. Complementary works such as retrospective core studies of fossil faunas are needed to quantitatively assess when and where A. confertitesta was introduced in Europe and potentially started to replace its congenerics A. veneta and A. aberdoveyensis.

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DOI: 10.3391/ai.2023.18.3.103350

Authors: Veijo Jormalainen, Essi Kiiskinen, Veera Hauhia, Sami Merilaita

Abstract: In the Archipelago Sea as in most other parts of the Baltic Sea, the bladder wrack (Fucus vesiculosus) is a foundation species of the littoral communities of the rocky shores. It sustains a community of epiphytic algae, herbivorous crustaceans and molluscs and various fish. Recently we have noticed a steep decline in the occurrence of the herbivorous crustaceans and molluscs in many sites in the Archipelago Sea. We hypothesise that a key factor contributing to this decline is the recent introduction of the Harris mud crab (Rhithropanopeus harrisii), which was first sighted in 2009 in this region. Importantly, because there are no native crabs in the northern parts of the Baltic Sea, the mud crab is a completely novel kind of predator in the ecosystem and the herbivorous crustaceans and molluscs may be particularly susceptible to it. Here, we document a dramatic decline of the typical herbivores occurring on the bladder wrack, possibly indicating an ongoing regime shift, by comparing our recent samples from across the Archipelago Sea with data collected a decade before the sighting of the mud crab. Moreover, we demonstrate a spatio-temporal association between the decline, particularly of the key herbivore species, the isopod Idotea balthica, and the establishment of the mud crab. We also present experimental evidence for a strong predator-prey -link between the mud crab and the isopod I. balthica. Finally, we discuss the possible consequences of the community change and scrutinise alternative explanations for our observations.

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DOI: 10.3391/ai.2023.18.3.108128

Authors: Robin P. M. Gauff, Marc Bouchoucha, Amelia Curd, Gabin Droual, Justine Evrard, Nicolas Gayet, Flavia Nunes

Abstract: Introduced species constitute a critical bio-security issue worldwide and the precise monitoring of their spread is crucial for their management. For species forming cryptic complexes this may remain difficult. Using integrative taxonomy, we formally report for the first time, well-established populations of the cosmopolitan introduced bryozoan Watersipora subatra in the French Mediterranean Sea and compile worldwide existing genetic data for Watersipora species alongside newly acquired data to establish the most complete phylogeny of the genus to date. This revealed pervasive erroneous identifications in Genbank, which in turn perpetrate further errors in recent studies, primarily misidentifying W. subatra as W. subtorquata. High abundance and geographic spread of W. subatra in our Mediterranean sampling sites suggest that this species has been present for some time but has been misidentified until now. We provide an updated species identification for all current reference sequences in the Watersipora genus, which may help future monitoring of W. subatra and other Watersipora species.

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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.2023.18.2.104092

Authors: Sergii Bushuiev, Sergii Snigirov, Mikhail O. Son, Ievhen Sokolov, Genadiy Kharlov, Yuriy Kvach

Abstract: At this time East Asian river prawn Macrobrachium nipponense is present almost everywhere in the lower reaches of the Danube and Dniester basins, in the Danube-Dniester interfluves and water bodies to the east of the Dniester. Successful adaptation and favorable climatic conditions in recent years have provided a significant increase in the East Asian river prawn populations in the Danube and Dniester. High growth rates of M. nipponense have been observed in the Danube and Dniester. In these river basins, higher values of maximum body length of the prawn (males 115 mm, females 87 mm) than those recorded in the native range water bodies and the cooler water bodies of thermal power plants during introduction were recorded. In small shallow brackish-water reservoirs of the region (PSU 1.5–6.0) the growth rate of M. nipponense is significantly lower than in the freshwater Danube and Dniester deltaic zones. Female East Asian river prawn in such water bodies mature at a much smaller size. The egg-laying period of female M. nipponense in the Danube lasts from June to October. The peak of egg laying is observed in July and August. There have been reported cases of M. nipponense being affected by crustacean burn-spot disease. The prospect of organizing the fishing of M. nipponense in the Danube River has been determined. It is necessary to continue research to increase selectivity of fishing gears, determination of optimal terms of fishing, and places of installation of fishing gears.

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DOI: 10.3391/ai.2023.18.2.105240

Authors: Jakub Fedorčák, Peter Križek, Ján Koščo

Abstract: Within the genus Carassius Jarocki, 1822 , the crucian carp (C. carassius L., 1758) occurs naturally in the northern part of Middle Danube Basin (Austria, Morava, Slovakia). This species has the least concern status in this region, but observations in the last decades suggest that it is very close to extinction here. The distribution of crucian carp is limited to a small number of vanishing lentic habitats (oxbow lakes, marshlands). These biotopes are in the last stage of succession due to the drying up of the landscape and a reduction in the creation of new natural alluvial habitats. The non-native cyprinid, C. gibelio (Bloch, 1782), known as gibel carp and Prussian carp, has gradually become eudominant in a wide spectrum of habitats/biotopes since the 1960s Several biological adaptations of non-native species are generally considered the strong basis for the mass spreading in the invaded area. The other side of the expansion of non-native C. gibelio is affected by anthropic activities associated with fish farming, translocation and stocking the fish in open water ecosystems. In this study, we analysed historical scientific data on the distribution of Carassius spp. published from the 19th century to the present from the mentioned areas. The results suggest that the number of records of invasive C. gibelio has gradually increase in rivers, regulated channels and creeks, which could be considered as natural pathways of spreading. However, the presence of invasive C. gibelio in artificial biotopes (fishponds, reservoirs) is continuous from the 1960s. In the area mentioned, the artificial biotopes are managed by national fisheries associations and relate to the historical way of farming in Central and Eastern European countries. To show the current state of the fishing grounds of the Slovak Angling Association, we a created the distribution map based on the Carassius spp. catches recorded in last two decades.

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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.2023.18.2.106252

Authors: Nicolas Spilmont, Laurent Seuront

Abstract: Behavioural interactions between introduced predators and introduced prey are still largely underestimated. The present work takes advantage of the co-occurrence of two introduced species, the Asian shore crab Hemigrapsus sanguineus and the amphipod Ptilohyale littoralis, respectively first recorded on rocky shores along the French coast of the eastern English Channel in 2005 and 2016. In this context, the predation by male and female H. sanguineus on P. littoralis was examined under controlled laboratory conditions, by presenting either juveniles of the blue mussel Mytilus edulis or adult P. littoralis to H. sanguineus. We subsequently assessed the potential prey preference of the Asian shore crab for P. littoralis and M. edulis by presenting the two prey items simultaneously in the same proportion. In the absence of choice, male H. sanguineus preyed significantly more on M. edulis than P. littoralis. In contrast, females preyed significantly less on M. edulis than P. littoralis; however, male and female H. sanguineus consumed similar numbers of P. littoralis. When choice was possible between P. littoralis and M. edulis, the crab did not exhibit preference stricto sensu for any type of prey. These results suggest that the Asian shore crab cannot be considered as a naive predator when confronted to a newly introduced prey. Our results also suggest that the amphipod P. littoralis did not exhibit any effective antipredator response towards the crab. These observations nevertheless warrant further work on the effects of abiotic factors (e.g. temperature) as well as other biotic interactions (e.g. presence of other prey or predators for H. sanguineus) may have on the observed prey-predator interactions between H. sanguineus and M. edulis and P. littoralis.

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DOI: 10.3391/ai.2023.18.2.104960

Authors: Isa Wallin Kihlberg, Ann-Britt Florin, Karl Lundström, Örjan Östman

Abstract: The mesopredatory round goby (Neogobius melanostomus) is an important fish invader in fresh and brackish waters of the northern hemisphere. Trophic interactions of invasive species can generate ecological impacts across the food web in invaded ecosystems. Here we investigated major diet components, spatiotemporal variation in diet and the effect of round goby densities on diet composition in two geographically distinct round goby populations in the Baltic Sea. The round goby is a generalist feeder but previous diet studies, based on visual prey identification, have likely over-emphasized the importance of hard-shelled, invertebrate prey in round goby diet, as shells degrade and evacuate slowly relative to soft-bodied prey that break down rapidly in the stomach. We therefore, in addition to visual stomach content analysis, used DNA metabarcoding, which is less biased towards hard body structures of prey and can be used for species assignment of highly degraded prey. The results demonstrated that round goby diet composition varied between areas and years. Visual stomach content analysis indicated that blue mussel was the main prey in the southern area, whereas hydrobiid gastropods were the major diet component in the northern area. Metabarcoding revealed that several fish species, likely the egg or larval stages of e.g. stickleback, cod and herring, were also part of the round goby diet. Analyses suggested that round goby feeding on fishes was positively associated with round goby densities. Our study shows that round goby, in addition to benthic invertebrates, preys on several fish species of ecological and commercial importance. Thus, there is potential for predator-prey reversal and negative effects of the invasive round goby on large, predatory fishes.

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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.2023.18.1.103438

Authors: Aylin Ulman, Hasan Deniz Akbora, Ozgur Çanak, Elaine Chu, Burak Ali Çiçek, Hasan Ersönmez, Sinan Mavruk, Caner Enver Özyurt, Taner Yildiz, Amy Liu, Nazli Demirel, Daniel Pauly

Abstract: The highly toxic orange-spotted toadfish Torquigener hypselogeneion (Bleeker 1852) [conspecific Torquigener flavimaculosus Hardy & Randall, 1983] is now a very common invasive fish in the Eastern Mediterranean. Its small size, well under 20 cm, may have concealed the danger it represents, and little is known about its biology or ecology. Here, the spawning seasons, gonado- and hepato-somatic index and condition factors of T. hypselogeneion from 3 locations of the Eastern Mediterranean are presented, based on a total of 1360 individuals sampled, i.e., 216 from Finike, 817 from Fethiye (both Turkey), and 327 from Cyprus. Our results show that T. hypselogeneion is a carnivorous species that forages on sandy bottoms, with a preference for small invertebrates, especially the small invasive gastropod Cerithium scabridum, crustaceans (hermit crabs, other crabs and barnacles), and sea urchins; however, at least in some localities, they appear to forgo eating during their peak reproductive period. The parameters of the von Bertalanffy Growth Function for T. hypselogeneion in the Eastern Mediterranean were: asymptotic length = 17.4 cm (total length; TL) and K = 0.96 year-1, implying a longevity of about 4 years, while the mean length at first maturity was about 10 cm (TL) for both sexes. An average-sized adult female (13 cm TL, 45.7 g live weight) was found to contain 1,250 eggs per gram body weight. Based on its high invasiveness and negative impacts to ecology of the Eastern Mediterranean and the human health, we suggest that T. hypselogeneion should be listed as a priority invasive species and that its population closely monitored within the Mediterranean Sea.

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DOI: 10.3391/ai.2023.18.1.103512

Authors: Vincent M. P. Bouchet, Jean-Charles Pavard, Maria Holzmann, Mary McGann, Eric Armynot du Châtelet, Apolyne Courleux, Jean-Philippe Pezy, Jean-Claude Dauvin, Laurent Seuront

Abstract: The invasive benthic foraminifera Trochammina hadai has been found for the first time in Europe along the coast of Normandy. Its native range of distribution is in Asia (Japan and Korea), and it has also been introduced along the coasts of western North America, Brazil and Australia. Morphological and molecular assessments confirm that specimens found in Le Havre and Caen-Ouistreham harbors belong to the Asiatic type. Like in Asia, T. hadai was found in transitional waters with muddy sediments. It exhibited high relative abundances (up to about 40%) confirming that T. hadai is a highly competitive species. In the present study, it was nearly absent from natural transitional waters and very abundant in heavily modified habitats like harbors, suggesting that ballast waters may likely be the vector of introduction. It was not recorded farther north along the coast of the Hauts-de-France. It is further hypothesized that the finding of a few specimens outside the harbor may facilitate the expansion of T. hadai in the English Channel by means of propagules dispersion.

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