DOI: 10.3391/ai.2026.21.3.199579

Authors: Seongjae Kim, Taekjun Lee, Jeounghee Lee

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

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DOI: 10.3391/ai.2025.21.3.203309

Authors: Lidia Garcia, Jennifer L. Ruesink, Andy Suhrbier, David Beugli, Rachel Flannery, Lindsey Parker, Emily W. Grason

Abstract: Estuaries are highly invaded ecosystems exhibiting many novel species interactions. This project addressed how predation from native and non-native crabs influences density of non-native clams along an estuarine gradient in Willapa Bay (Washington, USA). Recruitment of both Manila clams (Ruditapes philippinarum) and soft-shell clams (Mya arenaria) was greater up-estuary (south), likely from retention of locally-produced larvae. Three independent predator trapping efforts had higher catch of non-native European green crabs (Carcinus maenas) towards the ocean (north), setting up opposing predator and prey densities for exploration of top-down effects. Dungeness crabs (Metacarcinus magister) were 87% less abundant than green crabs and showed no regional difference in density in the single trapping effort where they were counted. Two field experiments investigated whether protection from nets impacted clam counts along the estuarine gradient. Excluding predators significantly increased survival of small Manila clams in both experiments, despite differences in duration, spatial scale, and whether clams were outplanted. Large Manila clams benefited only in the longer experiment. However, the protective effect of nets was unrelated to green crab catch, suggesting that the range of abundances observed in Willapa Bay during this study did not result in an additive mortality effect on clams. While abundances currently remain lower than other locations where impacts to clams have been documented, green crabs have increased rapidly in the past decade, and densities will likely continue to grow, particularly in the southern portion of the estuary. Thus, the lack of detected predation effects by green crabs in these experiments could be a transient phenomenon dwarfed by other post-recruitment losses of clams.

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DOI: 10.3391/ai.2026.21.3.200590

Authors: Miranda N. Andersen, Geethen Singh, Tamara B. Robinson

Abstract: Effective management of invasive alien species relies on spatial and temporal data. Yet, such information is scarce in the marine realm due to challenges associated with monitoring in highly connected environments that can be difficult to observe. As a result, many marine invasions remain poorly documented, hindering management. One such case is that of the European daisy anemone Cereus pedunculatus Pennant, 1777 in its invaded range of South Africa. Until recently, this alien anemone was thought to be restricted to the Langebaan Lagoon marine protected area (MPA), where occurrence records are seldom updated. The recent detection of C. pedunculatus in a distant estuary highlights the potential for further spread. To inform the management of this species, this study updated occurrence and abundance records in Langebaan Lagoon MPA and identified potential invasion hotspots using an ensemble-based species distribution model. Field surveys revealed that the anemone has expanded into six new areas of the lagoon since 2013. Modelling results indicate highly suitable conditions for the anemone at 31 sheltered sites along the coast of South Africa, including four sites within MPAs (i.e. Namaqua National Park MPA, Betty’s Bay MPA, Stilbaai MPA, and Goukamma MPA). Given this invasion risk, management agencies should employ routine monitoring and develop contingency plans for these sites to ensure adequate preparedness for future incursions of the species. Additionally, countries with climatically suitable regions, including Argentina, Australia, Denmark, New Zealand, Norway, and the United States, may consider including C. pedunculatus on national watchlists.

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DOI: 10.3391/ai.2026.21.2.189571

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

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

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DOI: 10.3391/ai.2026.21.1.180751

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.2026.21.1.183198

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

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

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DOI: 10.3391/ai.2026.21.1.181535

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

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

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DOI: 10.3391/ai.2025.20.4.175531

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

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

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DOI: 10.3391/ai.2025.20.4.164778

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

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

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DOI: 10.3391/ai.2025.20.4.175069

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

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

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DOI: 10.3391/ai.2025.20.4.166447

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.2025.20.3.153638

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

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

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DOI: 10.3391/ai.2025.20.2.152871

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

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

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DOI: 10.3391/ai.2025.20.2.150239

Authors: Nicholas T. Lewis, Sarah R. Goodnight, Daya Hall-Stratton, Amy E. Fowler

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

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DOI: 10.3391/ai.2025.20.2.153557

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

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

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DOI: 10.3391/ai.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.2025.20.2.153623

Authors: Andrew A. Davinack

Abstract: The assumption that elevated genetic diversity in a population directly correlates with its native range is a common but flawed approach in ecological studies. This practice is based on the belief that native populations, having been exposed to local evolutionary pressures over long periods, should exhibit higher genetic diversity, while introduced populations experience founder effects or bottlenecks that reduce genetic variation. However, multiple introductions and genetic admixture in non-native regions can artificially inflate genetic diversity, challenging the assumption that regions with high genetic diversity are the native ranges. This issue, which has been recognized for nearly two decades, remains prevalent in the literature despite strong evidence to the contrary. Studies on a variety of marine invertebrates demonstrate how introduced populations may exceed native ones in genetic diversity. In contrast, bottlenecks in native populations due to environmental stressors can mask the true genetic history of species. This letter argues for an integrative approach when determining native ranges, combining genetic data with historical, ecological and biogeographical analyses. This broader framework helps avoid misinterpretations of genetic diversity, which could lead to inaccurate conclusions about species’ native ranges and misinform conservation and management strategies.

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DOI: 10.3391/ai.2025.20.1.151447

Authors: Catherine E. de Rivera, Amy A. Larson, Benjamin G. Rubinoff, Luna R. Soto, Seth L. Wright, Edwin D. Grosholz, Gregory M. Ruiz, Andrew L. Chang

Abstract: The nature and strength of biotic interactions change along stress gradients, but the importance of these interactions across estuarine gradients is under studied. Here, we examined how consumption varies across estuarine salinity gradients by deploying standardized baits (‘squidpops’) to measure consumption pressure along the gradients of five estuaries in Oregon, USA. The relationship between consumption and stress was nonlinear: consumption pressure peaked slightly at mid salinity and decreased at low salinity, especially as temperature increased, in the five estuaries studied. This finding does not support either of two existing models for consumption across gradients, including the Consumer Stress Model and a consumer extension of the Salinity Range Model. The pattern of consumption aligns better with the Prey Stress Model or the Invasion Stress Model, and the latter predicts that successful invasion by stress-tolerant predators extends consumption pressure further upstream along estuarine stress gradients than the Consumer Stress Model. Although these estuaries have been invaded by the crab Carcinus maenas, our catch data did not support the expected greater numbers of these invasive, stress-tolerant predators mid estuary or an expected relationship with native predators, as C. maenas was trapped in low abundance throughout each estuary. While our catch data did not directly support the Invasion Stress Model, we found that individual C. maenas ate more squid in lab experiments when at intermediate salinities than fresher salinities. Overall, our field and lab results suggest consumption peaked at mid estuary, at intermediate to high stress, in these temperate estuaries. The Invasion-Stress Model needs more testing to evaluate whether it, the Prey Stress Model, or a new model is best supported and can predict ecological impacts from changes in precipitation patterns and biological invasions, as well as other environmental stressors for estuarine food webs.

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DOI: 10.3391/ai.2025.20.1.134814

Authors: Timothy S. Lee, Amy E. Fowler, Stacy A. Krueger-Hadfield, Chloe Gabriel, April M. H. Blakeslee

Abstract: Non-native foundation species may alter physical environments and provide habitat, thereby impacting recipient communities. Along the US east coast, we assessed biogeographic patterns of free-living and parasitic community diversity associated with the non-native red alga Gracilaria vermiculophylla, which is characterized by fixed (with holdfast) or free-floating thalli depending on the availability of hard substratum. In summer 2019, we surveyed 17 sites across 3 biogeographic regions. We used a random quadrat design to collect G. vermiculophylla and associated mobile macroinvertebrates per site, and we took abiotic measurements. We also haphazardly collected 100 Ilyanassa obsoleta snails per site to assess trematode diversity. In the lab, macroinvertebrates were removed from thalli and identified to lowest taxonomic level, and snails were dissected to determine trematode prevalence and diversity. Biotic and abiotic variables were analyzed for the best sets of predictors for species richness, abundance, and diversity of macroinvertebrates and trematodes across bioregions. Gracilaria vermiculophylla biomass was used as an offset in free-living analyses. Across all our US east coast sites, we detected 10,113 free-living (mobile) macroinvertebrates across 39 taxa. Three Gammaridean amphipods (Gammarus mucronatus, Ampithoe longimana, and Gammarus lawrencianus) comprised >50% of all detected organisms. We found biogeographic region to be a key predictor of macroinvertebrate abundance and richness. Trematode prevalence and richness were best explained by G. vermiculophylla biomass, while biogeographic region best explained diversity. As a widespread invader, our study provides evidence for associations that have formed as this foundation species has become established outside its native range. Over time, the presence and spread of G. vermiculophylla could continue to impact macroinvertebrate structure and diversity, and future work should directly compare macroinvertebrate communities with G. vermiculophylla to other foundation species along coastlines it is now common.

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DOI: 10.3391/ai.2025.20.1.136400

Authors: Elena K. Kupriyanova, Guillemine Daffe, Samaneh Pazoki, Manal Al-Kandari

Abstract: Spirobranchus tetraceros (Schmarda, 1861), originally described from New South Wales, Australia, was later reported as a widely distributed succesful species of Indo-Pacific origin, including as Lessepsian migrant to the Mediterranean, until evidence has accumulated that the nominal taxon is a large complex of morphologically similar species. Specimens of Spirobranchus cf. tetraceros recently discovered in the Western Mediterranean (Valencia, Spain) morphologically resembled those of S. multicornis from the Red Sea rather than S. tetraceros sensu stricto from Australia. However, genetic studies proved that sequences of the introduced specimens match neither those of the S. tetraceros morphotype from warm temperate Australia (NSW) nor those of S. multicornis from the Red Sea. Subsequently, Kupriyanova et al. (2022) designated a neotype of S. tetraceros from New South Wales supported by DNA sequence data and demonstrated that several species of the S. tetraceros complex exist in Australia alone. This study examined several populations of the S. tetraceros complex world-wide in search of the source population for the Western Mediterranean invader and demonstrated its identity with S. arabicus widely distributed in the Persian (Arabian) Gulf.

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DOI: 10.3391/ai.2025.20.1.143501

Authors: Jeffrey G. Blumenthal, Andrew L. Chang, Brian S. Cheng, Ellen M. Hines, Leora Nanus, Chela J. Zabin

Abstract: The Atlantic oyster drill Urosalpinx cinerea is an introduced predatory gastropod that has negatively impacted Olympia oyster restoration in multiple estuaries on the west coast of the United States. In San Francisco Bay, California, Atlantic oyster drills have a patchy spatial pattern of presence and absence and occur in a range of densities where they are present. This variable population distribution and a limited understanding of their local dispersal history poses a challenge to oyster restoration site selection. To address this dilemma, we evaluated five abiotic habitat factors as potential determinants of drill distribution. In 2017 and 2018, we compared quarterly drill abundance data to substrate composition, elevation, water temperature, salinity, and inundation at eight sites in Richardson Bay, a small embayment in San Francisco Bay. Using generalized linear mixed effects models, we found that amount of coarse substrate and elevation were positively and negatively, respectively, associated with drill population density at the four sites where drills were present. None of the five habitat factors, however, explained the absence of drills from the other four sites. These findings suggest ways for oyster restoration practitioners to select sites that optimize the chances oyster and drill co-existence or minimize the risk of drill invasion and point to the need for extreme caution against accidental introductions of drills to novel areas with suitable habitat. We recommend extensive drill population surveys in regions where Olympia oyster conservation is taking place coupled with additional fine-scale environmental data to better understand Atlantic oyster drill biogeography and to improve the odds of success of future Olympia oyster restoration work.

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DOI: 10.3391/ai.2025.20.1.145912

Authors: Jackson T. Hoeke, Kerstin Wasson, Amanda S. Kahn

Abstract: Hymeniacidon perlevis is a cosmopolitan sponge with a seasonal life cycle. We investigated seasonal and interannual dynamics of H. perlevis in Elkhorn Slough estuary, where it is an introduced species, and explored correlations between sponge cover and environmental conditions. We used sponge cover to estimate the potential effects of H. perlevis on its environment, and how those could vary across its seasonal life cycle. We found that recruitment is currently restricted to the upper estuary and while it varies annually, the frequency and density of sponge recruits have generally increased from 2007 to 2023. A seasonal life cycle was confirmed for Elkhorn Slough populations, consistent with other temperate populations of the species, with sponge cover peaking in October and declining to a minimum from March to May. Time-lagged Spearman-ranked cross-correlations suggest that sponge cover correlated with warmer temperatures and lower dissolved oxygen at all sites, with a time lag of 2–4 months. Precipitation from severe winter storms in 2023 also coincided with declines in sponge cover. Over the course of two years, we estimated that H. perlevis biomass and potential for water filtration are greatest in fall—corresponding with peak cover, and weakest to nonexistent in the spring. Understanding the seasonal and interannual dynamics of the H. perlevis population in Elkhorn Slough can inform future approaches to manage or mitigate its ecological impacts.

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DOI: 10.3391/ai.2025.20.1.134650

Authors: Emily M. Zavacki, Nathalie B. Reyns, Jeffrey A. Crooks, Michel A. Boudrias

Abstract: The non-indigenous bryozoan, Amathia verticillata, has a worldwide distribution and commonly colonizes anthropogenic structures such as docks. Although widely recognized to house marine invertebrates within its structure, little is known regarding how the biogenic material produced by A. verticillata influences the marine community dynamics. The purpose of this study was to document the temporal patterns of A. verticillata and their associated marine invertebrate community in an urbanized estuary, Mission Bay, San Diego, CA, USA. We quantified A. verticillata percent cover and the abiotic conditions between July 2021–2022. The percent cover of A. verticillata varied temporally with temperature, with highest percent cover on docksides when temperatures were warmest. We also collected A. verticillata colonies of varying morphology and size to determine if abundance, density, and diversity of the marine invertebrate community associated with A. verticillata was influenced by its biogenic material and structural complexity. All invertebrates were identified to the lowest taxonomic level possible. We identified 20 families, 19 genera, and 12 organisms to species, representing 2 non-indigenous species (NIS), 2 likely NIS, 3 cryptogenic, and 5 native species. The most abundant taxonomic groups were marine amphipods, isopods, tanaids, and polychaetes. Furthermore, we identified juvenile stages and females with eggs living within A. verticillata. The invertebrate community varied significantly by A. verticillata morphotype and structural complexity. In general, there was greater invertebrate diversity in the elongated versus compact morphotype, and the invertebrate counts and diversity increased with structural complexity. Collectively, our results suggest that A. verticillata functions as a habitat-producing ecosystem engineer that may be providing an important nursery habitat for diverse groups of marine invertebrates, including other NIS, on anthropogenic structures.

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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.2024.19.4.141420

Authors: Brent J. Bellinger, Stephen L. Davis

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

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DOI: 10.3391/ai.2024.19.4.141952

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.2024.19.3.131793

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

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

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DOI: 10.3391/ai.2024.19.3.134082

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

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

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DOI: 10.3391/ai.2024.19.2.119829

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

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

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DOI: 10.3391/ai.2024.19.1.114856

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.2024.19.1.115111

Authors: Ningning Chen, Yan Liu, Lin Yuan, Huixian Wu, Junzeng Xue

Abstract: Chthamalus challengeri Hoek, 1883 (Crustacea, Cirripedia) is typically found in the Bohai Sea and Yellow Sea along the coast of China. However, until 2009, it was never seen in the East China Sea. In 2010, C. challengeri was discovered at Yangshan Port in Zhoushan, East China Sea, and it has since been found to invade several islands in the Zhoushan Islands area successfully. Although the population that invaded Yangshan Port has disappeared in recent years, the population that successfully invaded the other islands in Zhoushan has been increasing in density. To study the ecological adaptability of C. challengeri larvae from the Zhoushan Sea Area, we conducted an experiment observing the larvae’s response to different temperatures and salinity gradients. The results indicate that the C. challengeri larvae are highly adaptable to different temperatures and salinities, and under temperatures ranging from 10–25 °C and salinities of 25–35, nauplius can complete all six stages of development and reach a settlement. We found that the survival and settlement rates during larval development were highest at 20 °C and salinity 30, which could be considered the optimum conditions for C. challengeri larvae. At these conditions, it took approximately 11.5 days for the larvae to undergo development from nauplius I to complete settlement. However, lower temperatures slowed down the development rate and settlement of C. challengeri larvae to some extent, while high temperatures can directly lead to the death of C. challengeri. According to the results of this study, the settlement period of C. challengeri in a new habitat can last as long as 7 months (April to November) compared to its original environment. This extended settlement period could provide favorable conditions for the long-distance dispersal of C. challengeri and enhance its invasive ability in new habitats.

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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.2023.18.4.114182

Authors: Kathryn A. O’Shaughnessy, Lorenzo Vilizzi, Wesley Daniel, Monica E. McGarrity, Hanna Bauer, Leslie Hartman, Stephen Geiger, Paul Sammarco, Steve Kolian, Scott Porter, Jessica Dutton, Matthew R. McClure, Michael Norberg, Alex Fogg, Timothy J. Lyons, Justin Procopio, Lauren Bantista, Wayne Bennett, Mary Wicksten, David Reeves, Julie Lively, Elizabeth Robinson, Jorge Brenner, Joseph Goy, Ashley Morgan-Olvera, Anna L. E. Yunnie, Gordon H. Copp

Abstract: Prevention of non-native species introductions and establishment is essential to avoid adverse impacts of invasive species in marine environments. To identify potential new invasive species and inform non-native species management options for the northern Gulf of Mexico (Alabama, Mississippi, Louisiana, Texas), 138 marine species were risk screened for current and future climate conditions using the Aquatic Species Invasiveness Screening Kit. Species were risk-ranked as low, medium, high, and very high risk based on separate (calibrated) thresholds for fishes, tunicates, and invertebrates. In the basic screening, 15 fishes, two tunicates, and 26 invertebrates were classified as high or very high risk under current climate conditions. Whereas, under future climate conditions, 16 fishes, three tunicates, and 33 invertebrates were classified as high or very high risk. Very high risk species included: California scorpionfish Scorpaena guttata, red scorpionfish Scorpaena scrofa, purple whelk Rapana venosa, and Santo Domingo false mussel Mytilopsis sallei under both current and future climates, with weedy scorpionfish Rhinopias frondosa, Papuan scorpionfish Scorpaenopsis papuensis, daggertooth pike conger Muraenesox cinereus, yellowfin scorpionfish Scorpaenopsis neglecta, tassled scorpionfish Scorpaenopsis oxycephalus, brush-clawed shore crab Hemigrapsus takanoi, honeycomb oyster Hyotissa hyotis, carinate rock shell Indothais lacera, and Asian green mussel Perna viridis under climate change conditions only. This study provides evidence to inform trans-boundary management plans across the five Gulf of Mexico states to prevent, detect, and respond rapidly to new species arrivals.

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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.2023.18.2.103850

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

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

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DOI: 10.3391/ai.2023.18.2.104203

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

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

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DOI: 10.3391/ai.2023.18.2.103208

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

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

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DOI: 10.3391/ai.2023.18.2.105436

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

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

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DOI: 10.3391/ai.2023.18.2.105548

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

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

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DOI: 10.3391/ai.2023.18.2.106252

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.2023.18.2.108485

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

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

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DOI: 10.3391/ai.2023.18.1.103610

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

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

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DOI: 10.3391/ai.2023.18.1.103301

Authors: Tuantong Jutagate, Wachira Kwangkhwang, Samnao Saowakoon

Abstract: The Australian red-claw crayfish (RCC) Cherax quadricarinatus (von Martens 1868) (Crustacea: Decapoda: Parastacidae) has been introduced and promoted for freshwater aquaculture in many countries including Thailand. This study i) evaluates the growth performance of RCC in near-natural conditions relative to captive conditions and ii) investigates how successfully RCC can compete with a trophically and functionally analogous native species. Growth of RCC was compared among two aquaculture systems (concrete tank and earthen pond) and a treatment with simulated natural conditions. After 12 months of rearing, total length and weight were greatest in the earthen pond and poorest in the near-natural treatment, with significant differences in total length between the near-natural treatment and the two culture systems. Length-weight relationships showed that the RCC had positive allometry in the culture systems but negative allometry in the near-natural treatment. Competition was evaluated by means of a biotic resistance test and an additive–substitutive experiment between RCC and the native freshwater crab Esanthelphusa dugasti (Rathbun, 1902) (Crustacea: Decapoda: Gecarcinucidae). Specific growth rates after 90 days of the experiments suggest that the crab inhibited growth of RCC. This implies that the invasion of RCC in Thai waters could be limited by competition from resident freshwater crabs.

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DOI: 10.3391/ai.2023.18.1.103389

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

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

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DOI: 10.3391/ai.2023.18.1.102938

Authors: Yollanda Carolina da Silva Ferreira Vançato, Joel Creed, Beatriz Grosso Fleury

Abstract: Invasive sun corals (Tubastraea spp.) are spreading along the Brazilian coast where they compete for space with native species, produce chemical compounds with antifouling and anti-predation properties and modify community structure and function. The tropical rocky shores of the Ilha Grande Bay were the first to be invaded in the southwest Atlantic and the Tamoios Marine Protected Area (MPA) within the bay was directly in the path of the spread of Tubastraea. MPAs aim to conserve biodiversity, preventing habitat loss and fragmentation and maintain healthy ecosystems. As healthy communities might better resist invasion the aim of this study was to investigate to what extent the benthic communities of the MPA are resisting the invasion. Baseline data on the abundance of the invasive corals Tubastraea spp. and community structure (cover) were quantified at eight sites over six years. The benthic communities were dominated by multispecies algal turfs, the mat-forming zooantharian Palythoa caribaeorum and the red alga Asparagopsis taxiformis and fell into five community groups two of which contained Tubastraea spp. The number of invaded sites increased over time as did the abundance of Tubastraea spp. in the communities. Tubastraea spp. sequentially invaded the studied communities within the MPA independently of differing community compositions – i.e. they did not offer better biotic resistance than unprotected areas. This was facilitated by the patchy nature of the communities which allowed Tubastraea spp. to get a foothold by initially avoiding species such as P. caribaeorum which offer greater biological resistance. At one site a significant reduction in Tubastraea spp. was detected after mechanical control. We conclude that the MPA’s status as a conservation unit was important to attract research and thus for establishing a baseline, quantifying change due to the invasion and focusing limited management resources, but not in providing significant biotic resistance to the invasion.

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