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.2025.20.2.150239

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.2025.20.1.143501

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.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.2024.19.3.134082

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.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.2023.18.1.103389

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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