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.2026.21.1.183198

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.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.2025.20.2.152871

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.2025.20.1.143501

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.2024.19.3.134082

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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