Biological Invasions

Introduced species can have profound impacts on communities by displacing and consuming native species. The intertidal communities in the Gulf of Maine have been radically altered through a suite of invasions including the herbivorous snail Littorina littorea and the omnivorous crab Carcinus maenas leading to morphological and spatial distribution changes in two native gastropod grazers (Littorina saxatilis and Littorina obtusata). Subsequently, another intertidal omnivorous crab Hemigrapsus sanguineus has become abundant in the intertidal, occurring in areas which were once refuges from crab predation. In order to quantify the potential impact of H. sanguineus on native snails, we conducted both in and ex situ experiments, testing the susceptibility of different sized snails to predation by introduced crabs. Additionally, we measured the distribution, abundance, and morphology of intertidal snails and crabs. Smaller snails of all species were the most susceptible to predation, although susceptibility differed among snail species. Littorina saxatilis was the most vulnerable to predation, with 73 and 64% of the population susceptible to large H. sanguineus and small C. maenas, respectively, while more than 89% of the L. littorea population was resistant to predation. Littorina saxatilis has been relegated to the high intertidal where there is high abiotic stress and poor-quality food, but until the invasion of H. sanguineus, there was little predation risk. Now, it seems that L. saxatilis is at the most risk of all three snail species, and may be at threat of local extirpation at locations with high populations of H. sanguineus.

Melanoides tuberculata (Thiaridae) is an old-world freshwater snail that is and now circumtropical. After being introduced in the 1960s via the aquarium trade, populations of M. tuberculata are thriving in spring systems of Texas (USA). Field surveys and experimental investigations of temperature tolerance suggest M. tuberculata is stenothermal, and thus range expansions outside of aquatic habitats with water temperatures between 18{degrees} and 32{degrees}C should be unlikely. However, in 2012 snails were detected in natural aquatic habitats with seasonal temperatures below the experimentally determined lethal thermal minimum. To test whether genetic and phenotypic variation might be associated with cold-water tolerance and range expansion, we sequenced the 16S ribosomal rRNA gene and measured qualitative conch morphology of 170 snails collected at 26 sites in three central Texas rivers. We also conducted phylogenetic analyses of M. tuberculata collected globally and in Texas to determine potential source populations and estimate the number of invasion events. Our results show snails detected in variable temperature habitats are genetically divergent and morphologically distinct from snails collected in habitats with stable temperatures. These data are consistent with at least three introduction events into Texas of M. tuberculata sensu lato that are characterized by distinct habitat preferences, physiological tolerances, and/or adaptive behaviors.

O_LIIn rivers, we are seeing a shift away from natural flow regimes towards larger and more frequent extreme drought and flood events. However, it is unclear how increasing intensity and frequency of extreme flow disturbances will play out alongside existing biotic pressures, such as biological invasions, to impact aquatic biodiversity. In New Zealand, vulnerable native non-diadromous galaxiid fishes face pressure from introduced trout through interspecific competition and predation, which may influence the recovery of native galaxiids after flood disturbances. C_LIO_LIHere, we employed a capture-mark-recapture study across 12 sites, along a gradient of disturbance following a major flood event, to examine the impact of extreme flooding on the population structure of non-diadromous galaxiids (Galaxias vulgaris and G. paucispondylus), and the effect of trout presence on individual galaxiid growth rates recovering from this event. C_LIO_LIWe found a lower abundance of all non-diadromous galaxiid size classes under higher flood magnitudes, but smaller size classes (i.e., young-of-year and 1-2 year cohorts) were more impacted. C_LIO_LIFurthermore, the presence of trout, whether at low or high abundances, reduced the individual growth of native non-diadromous galaxiids, despite interspecific effects being a weaker regulator of individual growth compared to conspecific effects. Moreover, trout effects on galaxiids varied by both galaxiid size and density, such that growth of smaller individual galaxiids in low densities were most affected by the presence of trout regardless of trout density. C_LIO_LIIn summary, our results demonstrate that non-diadromous galaxiid population dynamics in future are likely to be affected by flood disturbance regimes and introduced trout presence, the outcome of which involves a complex balance between reduced population persistence and increased individual resistance of larger individuals. C_LIO_LIConservation efforts that focus on maintaining strategically placed trout-free source populations of adult galaxiids could therefore be an important tool to enable native dispersal into trout-affected habitat and maintain population resilience in the face of increasingly larger and more frequent extreme events, given that recruitment of non-diadromous galaxiids is higher in the absence of trout. C_LI

Brook trout (Salvelinus fontinalis) is an invasive species in the Desolation Wilderness of California. But it is unknown to what extent this species is evolving to adapt to isolated high altitude lakes. We quantified morphological differences between three brook trout populations in Desolation Wilderness that are in isolation and of common origin. We took standardized photos of fish, created geometric nets of each specimen using points located at known morphological features, and performed a Procrustes superimposition and principal component analysis to examine and cluster morphological variation between individuals. Together, our results show morphological differences between three Salvelinus fontinalis populations in independent environments. Our results suggest that invasive species introduced from one source can show physical variation generations after introduction, and thus deserve attention for adapting to and perhaps becoming an increasingly complex part of their ecosystem.

Hylurgus ligniperda (F.) is a highly successful invader among bark beetles (Scolytinae) and forest insects in general. Native to the western Palearctic region, it has become established in every continent where its host plants (Pinus spp.) occur. Especially in southern hemisphere regions with large pine plantations, it is often highly abundant. As a repeat invader with a wealth of information on various aspects relevant for biological invasions, it is highly suitable as a model organism for studying the role of international trade, the planting of non-native trees, and the potential occurrence of bridgehead invasions (where abundant non-native populations precipitate further invasions). In the present study, our specific objectives were to reconstruct the worldwide invasions of H. ligniperda and the pathways involved by using a multi-pronged approach including population genetics, analysis of historic interception data generated from inspections of imports, and records of establishments in the literature. Our review of the native and non-native ranges of H. ligniperda and the chronology of establishments revealed at least 13 separate invasions of non-native regions, beginning with Madeira (Portugal) before 1850, and, most recently, eastern China in 2019. We compared the population genetics of 464 specimens from eight countries in the native range and eight countries in the non-native range. Sequencing of the mitochondrial COI gene revealed the presence of 29 haplotypes in six well-supported clades, based on a Bayesian analysis. Non-native populations had significantly lower haplotype diversity (mean h = 0.219) than populations in the native range (mean h = 0.691). Countries in the non-native range had an average of about two haplotypes compared with about four haplotypes in native countries. In the non-native range, only one or two haplotypes were dominant, and these differed among invaded regions except for haplotype HL-H3 which occurred in Australia, New Zealand and China as well as in four countries in southern Europe, and HL-H4 which was dominant in New Zealand, California, New York State, and eastern China as well as two countries in southern Europe. Analyses of interceptions of H. ligniperda with imports arriving in five countries revealed that between 74% and 99% of interceptions originated from other non-native regions while in the USA, most interceptions were linked to imports from the native range beginning in the 1970s. Based on the combined evidence of the chronology of invasions, interception data, and analysis of haplotype distribution, we conclude that the early invasions (before 1950) probably all originated from the native range, while several of the more recent invasions probably originated from parts of the non-native range (suggestive of a bridgehead effect). However, it cannot be determined with certainty what the original sources of each of the invading populations were.

SummarySporobolus anglicus (C.E. Hubb) P.M. Peterson & Saarela (synonym Spartina anglica) is a highly invasive coastal weed that forms dense monocultures in intertidal mudflats and estuaries, displacing native reedbeds and associated fauna. Introduced to Aotearoa New Zealand from Britain in the early 1900s to aid coastal land reclamation, it became a conservation concern by the 1960s, prompting control efforts in the South Island from the 1970s. This study presents a detailed S. anglicus eradication case study from the Marlborough Sounds, where detections are nearing zero. We model changes in detection probability over time in Te Hoiere / Pelorus Sound, a complex estuarine catchment. We aim to inform control efforts and assess the effectiveness of ongoing management, by evaluating the probability of non-detection as a proxy for functional eradication. Using data from the Department of Conservation (DOC), we analysed detections across 79 search blocks between 2013 and 2024. A generalised linear mixed model was used to generate predicted detections through to 2040, using a modified dataset with pseudo-zero values for probable absences. The data were modelled as presence/absence with a binomial distribution, to identify the first year with a <0.01 probability of a positive detection (upper 99% confidence limit). Results suggest that by 2032, the likelihood of further detections under current management practices is remote, and that functional eradication may have occurred. We interpret this decline in detection probability as indicative of management success. Model outputs can support decision-making as to when active surveillance might reasonably be ceased. To accelerate the tail-end of eradication efforts, we recommend intensifying search effort and widening delimitations within the catchment over the next five years, to ensure removal of any remaining individuals. We also propose the use of environmental DNA as a cost-effective backstop for after operational wind-down. Implications for ManagersO_LIOur modelling predicts that S. anglicus detections in Te Hoiere / Pelorus Sound should decline to levels consistent with functional eradication by 2032, and may render continued manual surveillance uneconomical after this date. C_LIO_LIFull, regular and repeated surveillance of suitable habitats is needed within a five-year intensive monitoring period at the tail-end phase of eradication, as detections approach zero and managers consider withdrawal. C_LIO_LIWhile statistical analyses support eradication management decisions, absolute certainty of absence is unattainable. Decisions must balance technical feasibility with practical risk tolerance. C_LIO_LIEnvironmental DNA could provide an effective post-withdrawal monitoring tool, to allay the risk of re-invasion. C_LI

Amphibians are threatened worldwide by various environmental and anthropogenic factors, making non-invasive conservation studies particularly valuable. Newts are one example of a thus challenged amphibian group. In Austria, local population declines of newts have been observed, with the smooth newt (Lissotriton vulgaris) being strongly affected. In this study, skin swabs were used as a non-invasive method to gather DNA, combined with established microsatellite markers. We sampled 139 L. vulgaris individuals at ten sites in North Tyrol, Austria, and, for comparison, 22 L. vulgaris meridionalis individuals in Brixen, Italy. We genotyped all individuals and analysed their population structure. We demonstrate the presence of three distinct L. vulgaris population clusters and find differences in population structure between supposedly introduced allochthonous L. vulgaris individuals and autochthonous populations, as evidenced by differences in Bayesian clustering and elevated values of the fixation index FST. A captive population in a zoological garden, with origins in the Kramsacher Loar in the Tyrolean Unterland (eastern part of Tyrol), performed poorly in terms of conservation genetics, with low genetic diversity (number of alleles) and clear genetic differentiation from populations in the wild (high pairwise FST values with wild individuals, clear separation in cluster analysis). Habitat restoration programs are a crucial aspect of amphibian conservation, as they restore ecosystems that are critical to the animals survival. While breeding programs can play an additional role in the future, they must carefully consider genetic diversity to ensure resilient and viable populations, especially in the face of climate change and chytrid fungus infection. This study emphasizes the significance of considering the geographic origin and genetic diversity of newts in conservation efforts. It also serves as a foundation for future population genetic studies of newts in Austria.

The invasive European green crab (Carcinus maenas) poses a significant ecological threat due to its rapid global spread and disruptive impact on coastal ecosystems. In the Southwestern Atlantic, the northernmost population was recently recorded in the San Matias Gulf, offering a unique opportunity to study its demographic and life-history traits at the leading edge of its range. We assessed sex ratio, population density, size distribution, and the size at which 50% of females were ovigerous (SM50). Our findings revealed a male-biased sex ratio (1.79 males per female) and low population density (0.42 crabs m-2), suggesting early-stage establishment. Size-structure analysis showed a well-structured population with clear cohort separation in both sexes and evidence of two recruitment events. The size at which 50% of females were ovigerous was estimated at 61.48 mm. Although egg-bearing females exhibited a well marked seasonality, with highest prevalence from May to July, their presence nearly year-round suggests an extended reproductive period and adaptability to local conditions, which may be advantageous in recently established populations, facilitating invasion success. These traits, combined with the species ongoing range expansion, highlight the invasive potential of C. maenas and its possible ecological impacts on the San Matias Gulf. Simple SummaryCarcinus maenas is an invasive crab species that threaten coastal ecosystems around the world by competing with native species and damaging habitats. Recently, a population of this species was discovered in the San Matias Gulf in Argentina, marking its northernmost record in the Southwestern Atlantic. We studied its demographic and life-history traits and found a male-biased sex ratio and relatively low population density. Additionally, egg-bearing females were present nearly year-round, with an increase in their abundance from May to July, suggesting that this population is adapting well to local conditions and maintaining an extended reproductive period. Together, these findings point to an early stage of invasion with the potential for further expansion, posing risks to native species and north Patagonian ecosystems.

A widespread Typha (cattail) hybrid zone in southeastern Canada and northeastern USA comprises T. latifolia, T. angustifolia, and their hybrid T. x glauca. In this region the hybrid is considered invasive because of its detrimental impacts on wetlands and biodiversity. Researchers and managers are increasingly interested in tracking and controlling the spread of the invasive hybrid, but this can be hampered by challenges in differentiating taxa: while the parent species and F1 hybrids can often be identified from morphological characteristics, advanced-generation and backcrossed hybrids can be common, and these have obscured morphological distinctions among taxa. Here we present five species-specific genetic markers that differentiate T. latifolia, T. angustifolia, F1 hybrids, and advanced-generation/backcrossed hybrids. Unlike the pre-existing species-specific microsatellite markers, these markers require only PCR or PCR followed by a restriction enzyme digest, and can be visualized on an agarose gel. As a result, they require less specialized equipment than existing species-specific markers, and should therefore be useful for a larger group of practitioners. Future use of these markers could include monitoring range expansions, assessing the outcomes of restoration programs, and avoiding the unnecessary elimination of native Typha.

Invasive alien plant species pose a serious threat to biodiversity, especially in ecologically rich regions such as the Mediterranean Basin. Among the most affected habitats are coastal communities, which host many endemic taxa and provide valuable ecosystem services. One such invasive taxa is Kalanchoe xhoughtonii, an allegedly artificial hybrid. This plant, although having demonstrated strong invasive potential, still largely remains unrecognised as a taxon of concern in Mediterranean countries, at least in national official catalogues. In this study, we assess the impact of this hybrid on coastal communities, focusing on the European Union Habitat of Community Interest (HCI) 1240--"vegetated cliffs with endemic statices (Limonium spp.)"--at two sites along the southern coast of Catalonia (NE Iberian Peninsula). Between 2022 and 2025, we conducted field surveys to document the population size, growth stages, and spatial competition with native species. Additionally, we gathered 1,422 iNaturalist occurrences of K. xhoughtonii to map its distribution across the Mediterranean Basin, assess its presence within Natura 2000 protected sites and within protected areas, including the HCI 1240, and determine its potential spread using ensemble ecological niche modelling with bioclimatic variables. Our results show that K. xhoughtonii forms dense monospecific patches in the surveyed areas that compete for space with two native Limonium species in southern Catalonia. Moreover, we confirmed 713 naturalised occurrences in the Mediterranean area, 107 were located within Natura 2000 protected sites and 58 within the HCI 1240 included in protected sites. Ecological niche modelling indicates high climatic suitability across 93% of western and 59% of eastern Mediterranean Natura 2000 sites containing the HCI 1240. The findings of this study highlight the invasive potential of K. xhoughtonii and support its inclusion in national catalogues of invasive species across Mediterranean basin countries. The study calls for systematic monitoring of the spread and ecological impact of this hybrid species in coastal community habitats.

PREMISEMany plant invaders like the Japanese knotweeds are thought to colonize new habitats with low genetic diversity. Such species provide an opportunity to study rapid adaptation to complex environmental conditions. METHODSUsing replicate reciprocal transplants of clones across three habitats, we described patterns of phenotypic response and assessed degree of local adaptation. KEY RESULTSWe found plants from beach habitats had decreased height, number of leaves, leaf area, and biomass allocation to roots and shoots compared to plants from marsh and roadside habitats when grown in their home habitat. In the marsh habitat, marsh plants were generally larger than beach plants, but not different from roadside plants. There were no differences among plants from different habitats grown in the roadside habitat. Despite this evidence of differentiation in beach and marsh habitats, we found mixed evidence for local adaptation. In their "home site" plants from the marsh habitat had greater biomass than plants from the beaches but not compared to plants from roadsides. Biomass comparisons in other habitats were either maladaptive or not significant. However, plants from the roadside had greater survival in their "home site" compared to foreign plants. There were no differences in survival in the other habitats. CONCLUSIONSWe found phenotypic differentiation associated with habitats despite the low reported genetic diversity for these populations. Our results partially support the hypothesis of local adaptation in marsh and roadside habitats. Identifying whether these patterns of differentiation result from genetic or heritable non-genetic mechanisms will require further work.

The blue crab (Callinectes sapidus) is ecologically and economically important in Chesapeake Bay. Nursery habitats, such as seagrass beds, disproportionately contribute individuals to the adult segment of populations. Spartina alterniflora salt marshes are intertidal nursery habitats which may serve as a refuge from predation for juvenile blue crabs. However, the effects of various characteristics of salt marshes on nursery metrics, such as survival, have not been quantified. Comparisons of juvenile survival between salt marshes and other habitats often employ tethering to assess survival. Although experimental bias when tethering juvenile prey is well recognized, the potential for habitat-specific bias in salt marshes has not been experimentally tested. Using mesocosm experiments, we tested if tethering in simulated salt marsh habitats produces a habitat-specific bias. Juvenile crabs were randomly tethered and un-tethered in mesocosms at varying simulated shoot densities. Tethering reduced survival, and its effect was not habitat specific, irrespective of shoot density, as evidenced by a non-significant interaction effect between tethering treatment and habitat. Thus, tethering juvenile blue crabs in salt marsh habitat did not produce treatment-specific bias relative to unvegetated habitat across a range of shoot densities and survival of tethered and untethered crabs was positively related to shoot density. These findings indicate that tethering is a useful method for assessing survival in salt marshes, as with other nursery habitats including seagrass beds, algae and unstructured sand.

Red Knots (Calidris canutus rufa) rely on Atlantic horseshoe crab (Limulus polyphemus) eggs in the Delaware Bay to refuel during northward migration. Intensive harvest of horseshoe crabs in the 1990s contributed to declines in Red Knot numbers. In 2013, the Atlantic States Marine Fisheries Commission adopted an Adaptive Resource Management (ARM) framework to balance sustainable horseshoe crab harvest with ecosystem integrity and Red Knot recovery, requiring annual stopover population estimates. We estimated the 2025 passage population of Red Knots at Delaware Bay using a Bayesian analysis of a Jolly-Seber mark-resight model which accounts for population turnover and imperfect detection. We also evaluated change in migration timing between 2011 and 2025 with model-derived estimates of arrival at the Delaware Bay each year. The 2025 passage population was 54,043 individuals (95% credible interval: 47,926-61,928), an increase of approximately 17% over 2024 and only the second year since 2011 to exceed 50,000 individuals. Despite the increase, overlapping credible intervals across years indicate a stable stopover population. Migration timing has remained consistent, with 50% of the population typically arriving by 18 May and no evidence of advancement since 2011. These findings provide meaningful input for the ARM framework, supporting sustainable harvest of horseshoe crabs while maintaining adequate foraging opportunities for Red Knots and other shorebirds. Parts of the Introduction, Methods, and Appendices were originally published in Lyons (2024) and are summarized herein.

Invasive round goby Neogobius melanostomus have advanced eastward through the state of New York and provinces of Ontario and Quebec over the past two decades and are approaching Lake Champlain, one of the largest lakes in North America. This manuscript describes international efforts to monitor round goby populations during 2021-2025 on (a) the southern approach to Lake Champlain via the Hudson River and Champlain Canal, and (b) the northern approach to Lake Champlain via the Saint Lawrence River and Richelieu River. Monitoring utilized environmental DNA (eDNA), backpack electrofishing, beach seining, benthic trawling, and viral hemorrhagic septicemia virus (VHSV) testing. In the Champlain Canal, round goby were captured as far north as the downstream side of the C1 dam (97 kilometers [km] from Lake Champlain) while eDNA detections occurred as far north as the upstream side of the C2 dam (90 km from Lake Champlain). In the Richelieu River, round goby were captured as far south as Saint-Marc-sur-Richelieu (82 km from Lake Champlain) while the southern-most eDNA detections occurred near the Canadian side of the international border (4 km from Lake Champlain). Water temperature influenced habitat usage of round goby in the Champlain Canal, with catch rates in near-shore areas declining at < 10 {degrees}C. All VHSV test results were non-detections at the mouth of the Richelieu River, while one positive and two inconclusive results occurred along the Champlain Canal. Together, these data have informed multiple mitigation measures and have implications for management of aquatic invasive species across North America.

Coastal salt marshes serve as the margin between terrestrial and marine biomes, provide a variety of important services, and are dynamic ecosystems characterized by keystone species that shape trophic networks. In coastal salt marshes of the Eastern Atlantic and Gulf of Mexico, marsh periwinkle snails (Littoraria irrorata) exhibit high abundance and form critical trophic pathways as important herbivores and detritivores. Specifically, snails forage on Spartina alterniflora and associated fungal growth, for which L. irrorata may act as a top-down control on plant growth. Yet, L. irrorata occupies other salt marsh plants, suggesting its habitat niche may be broader than previously reported. Here, we documented snail densities and size distributions in a Louisiana (USA) salt marsh composed of multiple marsh graminoids and report the results of behavioral choice experiments designed to test snail habitat preferences as a potential mechanism underlying their field distribution. We observed higher snail densities on S. alterniflora stalks (283.0 snails m-2) than other plant species, however, snails were highly abundant on S. patens (115.6 snails m-2), Juncus roemerianus (94.8 snails m-2), and Distichlis spicata (56.9 nails m-2) with densities comparable or higher on all species than reported on S. alterniflora in other studies along the U.S. Atlantic and Gulf coasts. Snails found on S. alterniflora and J. roemerianus, both plants with tall and rigid stalks, were also larger than snails found on other plant species. In species preference experiments, snails preferred S. alterniflora over S. patens and D. spicata, but no clear preferences were observed between S. alterniflora and J. roemerianus, nor between any combinations of S. patens, D. spicata, and J. roemerianus. Finally, we found that snails preferred senescing and dead S. alterniflora tissue over fresh S. alterniflora. Interpreting these results in tandem, this study suggests L. irrorata snails have consistent patterns of field distributions that match their habitat preferences, and future studies should test potential processes driving snail habitat selection, such as dietary habits and predator refugia (i.e., climbing sturdy stalks to avoid aquatic predators). Considering the abundance and trophic role of L. irrorata in coastal salt marshes, snail behavior may be a key modulator for salt marsh trophic networks.

Silver carp Hypophthalmichthys molitrix, are a highly mobile aquatic invasive species in the United States. The James River, South Dakota, USA, is a tributary of the Missouri River and is considered the northwestern leading edge of their invasion front. Understanding silver carp movement patterns on the cusp of this invasion is key to combatting the northwestward expansion of the species. We used passive telemetry to observe large-scale movement patterns of silver carp in the James River, South Dakota. Fifty silver carp were implanted with acoustic transmitter tags in June 2021, and movement data was recorded over a 1.5-year period. Most individuals exhibited site fidelity and stayed within the James River throughout the duration of the study. We used environmental data (i.e., temperature, dissolved oxygen, daily mean discharge, the change in discharge over 24 h and 48 h) and movement data collected from passive telemetry receivers to understand and predict silver carp movement cues in the James River. Daily mean discharge ("flow") was the most important predictor of silver carp movement in the James River. As flow increased, the probability of movement increased from 59% (95% CrI: 34% to 81%) at 1.5 m3/s to 94% (95% CrI: 80 to 99%) at 100 m3/s. In this study, silver carp exhibited a high propensity for movement within the James River, especially during periods of high flow. To prevent further northwestward expansion of these fish, silver carp movements must continue to be monitored and removal and prevention of further range expansion must be prioritized.

Multiple populations of resident ecotype killer whales (Orcinus orca ater) inhabit the Northeast Pacific, but the southern resident killer whale (SRKW) population is the most at-risk. SRKWs were listed as endangered in the United States in 2005 and have since shown little sign of recovery. Several factors have been identified as key threats to this population, and previously published studies suggest the population may be energetically stressed. Underlying health risks, such as parasitism, may be contributing to this populations failure to recover, but little is known about parasite infections in living individuals from natural killer whale populations. To assess the prevalence of internal parasite infections in Northeastern Pacific killer whales, we examined scat from endangered SRKW (n = 25) compared to two conspecific populations of resident killer whales that are not in decline: northern resident (NRKW, n = 2) and southern Alaska resident killer whales (SARKW, n = 7), and one offshore killer whale (OKW, n = 1). We analyzed 35 fecal samples collected from 27 wild killer whales using both microscopic identification of parasite eggs and genetic detection of parasites through DNA metabarcoding. We used body condition indices derived from concurrent aerial photogrammetry to evaluate whether parasite infection status was associated with individual body condition. We found that most individuals sampled (94%) were positive for Anisakis spp. - a parasitic nematode known to inhabit the intestines of cetaceans. These infections were detected across populations, and were not correlated with body condition, based on limited paired data. These results suggest that Anisakis infection is widespread among resident killer whales of the Northeast Pacific. The widespread detections of Anisakis among the samples examined here emphasizes the need for further work to understand the potential health impacts of parasitic infections on individual killer whales, and potential synergistic effects with other environmental stressors.

O_LIMacroinvertebrates are a critical source of food for riverine fishes. Anthropogenic stressors can transform riverine macroinvertebrate communities, yet the consequences of such transformations to the fishes that feed on them are poorly understood. Changes in any combination of food abundance, accessibility or quality may be referred to as changes in the foodscape of fishes. Stressor-driven increases of inaccessible prey that are difficult for fish to detect, capture or ingest, may render foodscapes less profitable to fishes. C_LIO_LIWe examined how nutrient enrichment, fine sediment, acid mine drainage (AMD), flooding and drying reshape fish foodscapes by altering the accessibility of macroinvertebrate prey for two New Zealand river fishes, Galaxias vulgaris and Gobiomorphus breviceps. We determined relative accessibility of macroinvertebrate taxa and traits to these fishes by comparing the abundance of prey taxa and traits in the environment with their corresponding abundances in fish diets. To make these comparisons, invertebrate and fish gut samples were collected from the same river reaches, at the same times, over three years. Environmental DNA (eDNA) metabarcoding of fish gut contents facilitated efficient diet characterisation of over 700 fish guts. Finally, to determine how multiple stressors might affect fish foodscapes, we related invertebrate trait-specific accessibilities to published data defining how the composition of those macroinvertebrate traits varies along stressor gradients. C_LIO_LIMacroinvertebrate traits that were most accessible to fishes were those promoting detection (e.g., active foraging behaviours exhibited by crawlers and scrapers) and ingestion (e.g., moderate size, morphologies lacking defensive structures), typical of mayfly and free-living caddisfly larvae. In contrast, prey with traits inhibiting detection (e.g., small size and burrowing behaviour) and ingestion by gape-limited fishes (e.g., large size), were less accessible to the fishes we studied. C_LIO_LITrait abundance-stressor relationships revealed that that increasing fine sediment, nutrients, AMD and drying, and decreased flooding frequency, favoured macroinvertebrates with traits that erode accessibility to fishes. These results show that multiple stressors may decrease the profitability of fish foodscapes by filtering out macroinvertebrate prey with traits promoting accessibility to fishes. C_LIO_LIFood web approaches to understanding multi-stressor impacts are rare, but are necessary to understand how the effects of multiple stressors on primary consumers then go on to affect predators of higher trophic position. A major barrier to fish foodscape research is the difficulty and cost of estimating trophic networks. We discuss how eDNA metabarcoding, coupled with trait-based approaches may help overcome these barriers, enabling generalisable assessments of foodscape changes caused by multiple stressors. C_LI

Investigation of the genetic variation of Batrachochytrium dendrobatidis (Bd or chytrid fungus) in New Hampshire (NH) in the northeastern U.S. has shown the presence of genetic mutations which are currently undocumented in the literature. DNA was collected as part of a long-term monitoring project in New Hampshire to test for the presence of Bd in amphibian populations. In this monitoring project, we are detecting the presence of Bd in multiple populations, but the observed amphibians do not appear to have increased mortality or other symptoms related to the fungus. To further investigate the strain of Bd affecting NH amphibians, we sequenced samples that were collected in 2019, as part of your yearly monitoring effort. Utilizing the Basic Local Alignment Search Tool (BLAST) and sequences available on GenBank, we found that there are two different strains of chytrid in the observed NH amphibians. These strains are similar to strains noted previously in New England, but exhibit unique point mutations and in one case, a deletion. These variations could affect the impact that Bd has on amphibians in this region, and therefore could contribute to a better understanding of the variation in strains of chytrid and how they impact amphibian populations around the world. This study highlights the importance of monitoring efforts conducted at smaller, non-research institutions and we encourage other small institutions to take up similar monitoring efforts for Bd or other national or global conservation concerns.

The growing global horticultural trade is having a steadily increasing impact on the rate at which alien species are introduced into new areas, partly because horticultural trade also entails the unintentional dispersal of many contaminant species. Although there are reports about noteworthy occurrences of alien plant species in garden centres, this phenomenon has hardly been studied systematically. To bridge this knowledge gap, we conducted systematic field surveys in 12 garden centres in Hungary to assess their alien flora. We hypothesised that (i) the number of alien species inhabiting a garden centre is positively correlated with its size, (ii) relative to their size, garden centres host a disproportionately large proportion of the local alien flora, and (iii) alien species inhabiting garden centres differ from the regional alien flora in their traits. We recorded altogether 93,788 individuals of 67 introduced species, seven of which have not yet been reported from the country. There was considerable variability in the number of species and individuals found in each garden centre, but there was no correlation between the size of the garden centres and the number of species they host. Despite their relatively small size, the studied garden centres hosted a considerable proportion of the local alien flora, indicating that they strongly accumulate alien species and that they can act as invasion hubs for several alien species. Alien species inhabiting garden centres differed from the regional alien flora in some of their trait values, indicating that the species that are most successful at establishing populations inside garden centres are both good dispersers and possess an effective resource-acquisitive strategy. We conclude that established alien plant populations in garden centres may induce local invasions, and in the meantime, individuals and seeds inside the containers of ornamental plants are regularly transported to distant areas by the customers. Therefore, plant species dispersed as contaminants of horticultural stock need to be better considered in invasion biology to reduce the threat they may present.