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.2026.21.2.190069

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

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

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DOI: 10.3391/ai.2026.21.2.189571

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

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

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DOI: 10.3391/ai.2026.21.1.183198

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

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

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DOI: 10.3391/ai.2026.21.1.181535

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

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

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DOI: 10.3391/ai.2025.20.4.171920

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

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

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DOI: 10.3391/ai.2025.20.4.175531

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

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

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DOI: 10.3391/ai.2025.20.4.164778

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

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

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DOI: 10.3391/ai.2025.20.3.153638

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.2025.20.1.151447

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.2025.20.1.143501

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.2024.19.4.136332

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

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

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DOI: 10.3391/ai.2024.19.4.141420

Authors: Brent J. Bellinger, Stephen L. Davis

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

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DOI: 10.3391/ai.2024.19.3.133295

Authors: Kenneth J. Killgore, Jan J. Hoover, William T. Slack, James P. Kirk, Bradley R. Lewis, Steven G. George, Leandro E. Miranda

Abstract: Silver carp, Hypophthalmichthys molitrix, escaped into the Lower Mississippi River (LMR) over 50 years ago, established reproductive populations, and spread across much of the Mississippi River Basin. Demographic rates of silver carp are needed to inform decisions on control and management of this invasive species, but have not been published for the LMR. The purpose of this paper is to report silver carp age and growth estimates from fish collected in riverine (mainstem) and backwater (lake) habitats in the LMR during the period 2011–2019, to compare our results with populations from other geographic areas in the Upper Mississippi River drainage, and to evaluate latitudinal and habitat differences in demographic parameters. Silver carp gained weight with increasing length similarly throughout the lower and upper basin. However, annual growth rates were higher in the LMR compared to northern rivers including the Illinois, Wabash, Missouri, and Middle Mississippi rivers. In the LMR, regression analyses demonstrated that females were heavier in lakes than males or females in the mainstem and that females in lakes had the lowest instantaneous mortality (-0.186). Maximum age was 8 and 10 years for females and males, respectively. The largest male weighed 13.8 kg with a total length of 1022 mm, and was 7 years old. The largest female weighed 16.0 kg with a total length of 1034 mm TL, and was 7 years old. Rapid growth rates, larger sizes, and lower mortality in the LMR, in combination with limited commercial fishing, extensive river-floodplain connectivity, and vast amounts of spawning areas, ensure that LMR silver carp will continue to act as a source of fast-growing invasive individuals for other reaches and other rivers throughout the Mississippi River Basin.

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DOI: 10.3391/ai.2024.19.3.131793

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

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

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DOI: 10.3391/ai.2024.19.3.134082

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

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

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DOI: 10.3391/ai.2024.19.2.124660

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

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

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DOI: 10.3391/ai.2024.19.2.119829

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

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

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DOI: 10.3391/ai.2024.19.1.117603

Authors: Jeffrey E. Hill, Quenton M. Tuckett, Katelyn M. Lawson

Abstract: For non-native species, climate can act as a primary filter limiting establishment. Numerous studies examining climate similarity between native and introduced regions have been completed for temperate areas, however we know little about how well climate matching performs for warmer regions. For non-native freshwater fish introduced to warm regions, one potential problem with climate matching is that fish from both temperate and tropical source regions could establish. Our goal was to examine whether climate matching can predict the establishment of non-native freshwater fish for a warm climate region. We used CLIMATCH, a widely applied climate matching program, to analyze climate similarity between source and target regions for 37 successfully established species and 36 species that have failed to establish. CLIMATCH was calculated in two ways for successfully established species, with Florida records included (post hoc) and without Florida records (a priori). The mean post hoc score for successful species was higher than that of failed species; however, the mean a priori score for successful species did not significantly differ from failed species. On average, post hoc scores were inflated 1.5 times over a priori scores. The post hoc result is tautological—the scores are high because the species is successful, and the species is successful because the scores are high. These results highlight two issues for climate matching: (1) as commonly done post hoc, degree of climate match and predictive power may be overestimated and (2) a priori applications may lack predictive power. We recommend consideration of these issues in the use and interpretation of CLIMATCH for prediction. Additional research into regional importance of climate variables (temperature and precipitation) is warranted, especially in warm climate regions.

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DOI: 10.3391/ai.2023.18.4.112766

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

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

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DOI: 10.3391/ai.2023.18.4.114182

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.2023.18.2.104203

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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