Biological Invasions

In October 2023, several colonies of an alien soft coral species were reported on shallow reefs in southwest Puerto Rico. The soft coral was identified as a xeniid octocoral (species undetermined), resembling the octocoral Unomia stolonifera, which has invaded and overgrown reefs in Venezuela in recent years. To conclusively characterize the species of the invading xeniid, we employed multilocus barcoding targeting four genes (ND2, mtMutS, COI, and 28S) of three separate colonies across three locations in southwest Puerto Rico. Sequence comparisons with xeniid sequences from GenBank, including those from the genera Xenia and Unomia, indicated a 100% sequence identity (>3,000 bp combined) with the species Xenia umbellata (Octocorallia : Malacalcyonacea : Xeniidae). Xenia umbellata is native to the Red Sea and to our knowledge, this represents the first confirmed case of this species as an invader on Caribbean reefs. Similar to U. stolonifera, X. umbellata is well known for its ability to rapidly overgrow substrate as well as tolerate environmental extremes. In addition, X. umbellata has recently been proposed as a model system for tissue regeneration having the ability to regenerate completely from a single tentacle. These characteristics greatly amplify X. umbellatas potential to adversely affect any reef it invades. Our findings necessitate continued collaborative action between local management agencies and stakeholders in Puerto Rico, as well as neighboring islands, to monitor and control this invasion prior to significant ecological perturbation.

This study aims at synthesizing the recent invasion history of Carcinus maenas in the SW Atlantic (~20 years), particularly the northward expansion, based on available published papers, technical reports, and new field surveys. Our analyses extend the known distribution range northwards ca. 330 km. totaling ~1000 km along the Argentinean coast since its last detection in Nuevo Gulf in 2015. The expansion rate appeared to slow down during the last 15 years (from 115km/yr. to 30 km/yr.) as the species continues moving northwards into the transition zone between the Magellan and Argentinean biogeographic provinces (41{degrees}-43{degrees}S). In addition, a species distribution model (SDM) is provided at a much finer spatial resolution than previous studies, which accurately foresees suitable areas of invasion in the southern San Jorge Gulf, and predicts a hotspot of invasibility around 40{degrees}-33{degrees}S{degrees} if the invasion continues northward. Potential impacts of C. maenas on native species, particularly economically important oyster beds are discussed.

Restoration of barrier island and headland habitats can alter existing and create new habitats, which may impact wildlife occupying these areas such as the threatened Piping Plover (Charadrius melodus). We used resight data from banded birds to develop minimum convex polygon (MCP) and kernel density estimates (KDE) of individual Piping Plover home ranges to investigate whether changes in habitat use resulted from restoration activities at Whiskey Island and Caminada Headland, Louisiana. We quantified home range areas for each season and compared changes among pre-restoration, active restoration, and post-restoration phases at each site. We had sufficient sample sizes from Whiskey Island to compare home ranges derived by MCP during the pre-restoration phase to the active restoration phase. However, we did not have enough resight data to analyze post-restoration phase by MCP or any phase by KDE at Whiskey Island. For Caminada Headland, we were able to compare all phases of restoration using MCP, but only had sufficient data to compare pre-restoration and active restoration phases using KDE. Aside from one significant decrease in core (50% isopleth) home range at Caminada Headland when comparing MCPs between post-restoration ([~]8 ha) and pre-restoration ([~]11 ha) phases, we found no other differences in home range size across phases at either of our study sites. The sum of all evidence generally indicating no change to Piping Plover home range size suggests that barrier island and headland restoration did not have significant positive or negative impacts. The weak response to restoration activities further suggests that birds are using similar or smaller amounts of habitat after restoration is complete and may not need to expand their foraging range following restoration. Further study can help to understand how species of conservation concern respond to coastal restoration efforts, which is critical for establishing comprehensive conservation strategies aimed at species recovery.

BackgroundExtensive phenotypic plasticity in oysters makes them difficult to identify based on morphology alone, but their identities can be resolved by applying genetic and genomic technologies. In this study, we collected unknown oyster specimens from Hawaiian waters for genetic identification. MethodsWe sequenced two partial gene fragments, mitochondrial 16S ribosomal RNA (16S) and cytochrome c oxidase subunit I (COI), in 48 samples: 27 unidentified oyster specimens collected from two locations on O ahu, 13 known specimens from a hatchery in Hilo, Hawai i Island, and 8 known specimens from Hilo Bay, Hawai i Island. ResultsMolecular data identified approximately 85% of unknown samples as belonging to the Ostrea stentina/aupouria/equestris species complex, a globally distributed group with a history of uncertain and controversial taxonomic status. The remaining unknown samples were the native Dendostrea sandvichensis (G. B. Sowerby II, 1871), and nonnative Crassostrea gigas (Thunberg, 1793), the latter of which is a commercial species that was introduced to Hawai I from multiple sources during the 20th century. Phylogenetic analysis placed Hawai i Ostrea alongside samples from China, Japan, and New Zealand, grouping them within the recently classified western Pacific O. equestris. Until now, four extant species of true oyster have been documented in Hawai i. This study expands the known range of O. equestris by providing the first verification of its occurrence in Hawai i.

The first record of Halophila stipulacea is reported for the continental waters of the United States. In August 2024, a small meadow was identified inside Crandon Marina on Key Biscayne, Florida, USA. Following surveys have revealed that H. stipulacea has spread to adjacent areas immediately outside of the marina, often growing either in close proximity to, or interspersed with, the native seagrasses Thalassia testudinum, Syringodium filiforme, and Halodule wrightii. This serves as an initial report and extends the geographic scope of this introduced species in the Western Atlantic basin.

Invasive species are one of the major threats to global biodiversity, particularly in hotspots of endemic species, such as oceanic insular ecosystems. Tropical and subtropical islands are particularly vulnerable to biological invasions, with freshwater ecosystems expected to experience the most severe impacts. This is especially true if the insular freshwater fauna comprises a large set of near-threatened to critically endangered species. This study assesses the establishment of the pet-traded shrimp Neocaridina davidi and its parasites on the island of la Reunion, a biodiversity hotspot within the Malagasy region. We confirm the establishment of feral N. davidi in two river catchments. Moreover, we confirm the presence of the microsporidian Ecytonucleospora hepatopenaei, an economically and ecologically relevant parasite that might impact a wide range of native species, including those living in brackish and marine environments. Three other microsporidians, two of which are unknown, have also been detected for the first time in N. davidi, raising concerns over possible spillover-spillback events. Therefore, we recommend timely actions to curb the spread of N. davidi and its parasites in an effort to preserve the already endangered native freshwater fauna.

Habitat loss and fragmentation have caused global biodiversity loss. It is important to understand the impact of past land use on biodiversity, not only in the present, but also to inform appropriate land-use strategies. Most studies on extinction debt, the concept that past land use drives present organism distribution, focus on species richness. However, when focusing on individual species, species richness is based on presence-absence data and does not reflect abundance. Therefore, extinction debt may not be clearly evident in presence-absence data. However, few studies have compared the effects of past land use on organism distribution using both abundance and presence-absence data. In this study, we compared the effects of past land use on the abundance and presence-absence of the ezo salamander Hynobius retardatus. We surveyed the aquatic areas of Ezo salamander egg sacs along a survey route in northern Japan. We measured the percentages of past and present forest areas, the physical environment, water quality, and waterbody type. The number of egg sacs was significantly associated with the percentage of past forest area, physical environment, water quality, and waterbody type. The presence or absence of egg sacs was significantly associated with the physical environment and water quality. Our results suggest that the effects of past land use on organism distribution are more evident in abundance data than in presence-absence data. Researchers and land managers may need to consider the time lag before extinction based on abundance data to assess extinction risk accurately.

The great physiological, behavioral and morphological plasticity of salmonids contributed to the success of their introduction into a wide range of habitats. However, rainbow trout (Oncorhynchus mykiss) is the only salmonid species to live in the tropics. Like for any cold-water species, water temperature is assumed to be a major constraint to the presence and expansion of rainbow trout. In this study, we collected detailed records of the introduction history of rainbow trout at 35 sites across the island over 80 years, and we document the presence of self-sustainable trout at each site. We explored the linear relationship between water temperature and elevation.

Here, we report the first genetic confirmation of golden mussels (Limnoperna fortunei) in North America, and the subsequent development, optimization, and deployment of golden mussel eDNA monitoring procedures. Aquatic species invasions are economically costly, disrupt ecosystem functionality, and impact native aquatic communities. Early detection of new invasive species enables rapid response via implementation of effective eradication or control measures and is key for reducing harmful outcomes. Initial species detection and taxonomic identification can be aided by genetic methods that have high detection sensitivity and accuracy. Genetic methods such as environmental DNA (eDNA) sampling can be used to detect invasive species before they become established in new systems, providing an early alert system to inform resource managers. Golden mussels were first detected in North America in October 2024 near the Port of Stockton in the San Francisco Estuary (SFE). The SFE is particularly vulnerable to invasion due to the access and connectivity provided by the presence of engineering infrastructure and shipping lanes. Collaborative efforts between public agencies and academic institutions are underway to develop a coordinated detection and response plan. Early detection followed by a rapid response is the best defense against prolific invasive species, such as the golden mussel.

Long-term drought caused Lake Powell, a reservoir on the Colorado River (USA), to decline to its lowest elevation in >50 years during 2022-2023, allowing warm water to pass through intakes of Glen Canyon Dam and facilitating invasion by non-native Smallmouth Bass (Micropterus dolomieu). Establishment of bass downstream of the dam could threaten persistence of several native fishes, including two federally listed species. Subsequent detection of larval Smallmouth Bass in a spring-fed slough (river mile -12 slough) connected to the river in Glen Canyon National Recreation Area (NRA) increased urgency to stem further invasion. The National Park Service is evaluating proposed actions to limit effects from non-native predators on native species in the Colorado River, including potentially channelizing the slough. This locally rare, spring-fed waterbody provides habitat for other species, including Western Tiger Salamanders (Ambystoma mavortium subsp.) of uncertain origin. We found salamanders from the slough had two distinct mitochondrial DNA haplotypes identical to sequences from nearby Arizona Tiger Salamander (A. m. nebulosum) populations, confirming they are the native genotype. We detected Red-spotted Toads (Anaxyrus punctatus) and Woodhouses Toads (A. woodhousii) from three other sites in Glen Canyon NRA and 34 sites in adjacent, downstream Grand Canyon National Park (spanning [~]464 km of river) with environmental DNA and traditional surveys. However, we did not detect salamanders elsewhere, matching prior information that salamanders are rare in the Colorado River corridor below Glen Canyon Dam. Based on this information, we discuss management options for the local population of Arizona Tiger Salamanders.

Fistulobalanus albicostatus Pilsbry, 1916 (Thoracica: Balanidae) is a tropical to temperate species distributed in the NW Pacific. The previously known northernmost record of this species in Japan was from Aomori Prefecture, at the northern end of Honshu Island, Japan. However, field surveys conducted in 2023 and 2026 confirmed the occurrence of F. albicostatus in Hakodate Bay, the southern end of Hokkaido, Japan, across the Tsugaru Strait, thereby extending the northern limit of its known distribution. A line transect survey conducted in May 2026 recorded seven living individuals within an area of 128 m. F. albicostatus was rare on the mid-high shores, accounting for only 2% of all barnacle individuals in a quadrat survey. The basal diameter of the living individuals ranged from 0.76 to 1.23 cm, and all individuals possessed ovaries. Based on characteristics of both morphological and COI gene, the specimens were identified as F. albicostatus, and belonged to the same haplotype of populations that are present in Honshu Island. The establishment of F. albicostatus in Hokkaido suggests an ongoing northward range shift of this warm-water species, with the potential for further expansion under continued ocean warming.

Southeastern North America harbors the richest freshwater biodiversity hotspot in the northern hemisphere and is home to numerous species with extremely narrow ranges. Among these are the six species of the Etheostoma chermocki species complex, which exclusively inhabit small streams spanning fewer than 100 square kilometers in Alabama, USA. One of these species, the Birmingham Darter Etheostoma birminghamense, was described in April 2025 from Valley Creek and its associated tributaries, which extend into the urban core of Birmingham, AL, and its suburbs. At least one population of E. birminghamense is feared extirpated, highlighting the imperilment of this microendemic species. Here, we report the results of recent collections that extend the range extension of E. birminghamense into Little Blue Creek, Nabors Branch, Halls Creek, and localities in the mainstem of Valley Creek. As previously hypothesized, occurrences of E. birminghamense are associated with exhumed Cambrian-Ordovician- and Mississippian-age carbonate units, which in Little Blue Creek appear only as pockets of exposed bedrock at the base of the channel and on the banks. Our observations demonstrate that E. birminghamense is distributed throughout the majority of the Valley Creek drainage, highlighting the need for rapid assessment of its conservation status.

Early detection of invasive alien species is essential for preventing establishment and mitigating ecological impacts, particularly in island ecosystems harbouring evolutionarily isolated endemic species. Recently, despite increasing reptile introductions and their suggested widespread impacts, methods for monitoring arboreal invasive reptiles remain limited. This study addressed the need for practical detection tools by developing terrestrial environmental DNA (eDNA) sampling methods that collect DNA from leaf surfaces to detect the arboreal invasive green anole (Anolis carolinensis) in the Ogasawara Islands, Japan. Two methods, wiping leaf surfaces with gauze and rinsing with sprayed water, were tested. At an invaded site, green anoles were successfully detected in eight out of 10 samples in both methods. Although no significant difference in eDNA concentration was observed, the wiping method was selected for its greater simplicity. Subsequently, the relationship between green anole population density and eDNA concentrations detected using the wiping method was investigated, suggesting a significant positive relationship. This is the first report demonstrating that terrestrial eDNA concentrations can reflect arboreal reptile population density, suggesting potential applications in quantitative terrestrial biodiversity assessments. Furthermore, the successful detection of eDNA even in the extremely low-density habitat of the green anole demonstrates the usefulness of eDNA-based surveys for early detection of invasions. The method developed here may be broadly applicable to terrestrial biodiversity monitoring, especially in tree-dwelling taxa. Given accelerating biological invasions and biodiversity loss, this approach is expected to benefit managers, conservationists, and researchers concerned with terrestrial ecosystems.

Sea star wasting (SSW) has been described globally in over 25 species of asteroids. This condition is characterized by body wall lesions, loss of turgor and ray autotomy, which often results in the mortality of specimens. The cause of SSW has remained elusive. A recent report detailing a potential causative agent, Vibrio pectenicida FHCF-3 (Prentice et al., 2025), inspired an investigation into its occurrence in available genomic and transcriptomic data from 2013-2015 from wild specimens and those enrolled in experimental incubations. While Vibrio pectenicida FHCF-3 16S rRNA gene sequences were detected in abnormal body wall tissues of Pycnopodia helianthoides from public aquaria in 2013, they were not detected in grossly normal or abnormal body wall specimens of other species sampled concurrently at sites where mass mortality was observed and from public aquaria. Experimental amendment of Pisaster ochraceus with organic matter substrates led to enrichment of V. pectenicida FHCF-3 16S rRNAs at the animal-water interface, and that they surged in abundance 24h prior to body wall lesion appearance. However, in this experiment V. pectenicida FHCF-3 16S rRNAs were inconsistently detected in coelomic fluid of abnormal specimens, and their abundance at specimen surfaces was inversely related to coelomic fluid detections. Perplexingly, V. pectenicida FHCF-3 was detected in abnormal P. helianthoides treated with 0.2 {micro}m filtrates of homogenized tissues, but absent in grossly normal heat-treated filtrate controls in prior work. Vibrio spp, are copiotrophs that experience rapid growth to dominate microbial communities in plankton and tissues when amended to seawater in a mesocosm experiment. These patterns indicate V. pectenicida FHCF-3 might cause abnormalities in P. helianthoides under certain conditions, but its growth might be a secondary rather than primary determinant of disease (i.e. it is saprobic or an opportunistic agent). It remains possible that sea star wasting abnormalities in P. helianthoides represent a generalized response to bacterial infiltration, driven by a diverse set of bacteria which includes but does not require species such as V. pectenicida FHCF-3. Finally, our data suggest that this taxon is not intimately tied to SSW abnormalities in other species. Hence, V. pectenicida FHCF-3 may be a driver of a SSW disease in P. heliathoides, but cannot be the cause of all SSW across species.

Human-mediated introduction of plant and animal species into biogeographic ranges where they did not occur before has been so pervasive globally that many ecosystems are now co-invaded by multiple alien plant and animal species. Although empirical evidence of invaders modifying recipient ecosystems to the benefit of other aliens is accumulating, these interactions remain underexplored and underrepresented in heuristic models of invasion success. Many freshwater ecosystems are co-invaded by aquatic macrophytes and mollusks and at the same time experience nutrient enrichment from various sources. However, studies are lacking that test how nutrient enrichment and co-invasion by alien herbivores and plant species can interactively affect native plant communities in aquatic habitats. To test such effects, we performed a freshwater mesocosm experiment in which we grew a synthetic native macrophyte community of three species under two levels of nutrient enrichment (enrichment vs. no-enrichment) treatment and fully crossed with two levels of competition from an invasive macrophyte Myriophyllum aquaticum (competition vs. no-competition), and two levels of herbivory by an invasive snail Pomacea canaliculata (herbivory vs. no-herbivory) treatments. Results show that herbivory by the invasive snail enhanced above-ground biomass yield of the invasive macrophyte. Moreover, the invasive herbivore preferentially fed on biomass of the native macrophytes over that of the invasive macrophyte. However, nutrient enrichment reduced above-ground biomass yield of the invasive macrophyte. Our results suggest that eutrophication of aquatic habitats that are already invaded by M. aquaticum may slow down invasive spread of the invasive macrophyte. However, herbivory by the invasive snail P. canaliculata may enhance invasive spread of M. aquaticum in the same habitats. Broadly, our study underscores the significance of considering several factors and their interaction when assessing the impact of invasive species, especially considering that many habitats experience co-invasion by plants and herbivores and simultaneously undergo varous other disturbances including nutrient enrichment.

In recent decades, the Mediterranean Sea has experienced a marked escalation in the introduction of non-native and invasive marine species. The global expansion of aquaculture, coupled with the increased movement of commercial species, has raised concerns about the potential for introducing parasites into new environments, posing a growing threat to marine ecosystems. Polydora websteri is a shell boring polydorin worm that induces the formation of mud-filled blisters within the shells of molluscs. The annelid is considered indigenous to the Asian coasts and has been documented in various locations across the globe. In the present work, we report a massive presence of P. websteri in several sites of the North Adriatic costline and we provide some diagnostic features that are useful to identify the species. Polydora websteri can be distinguished of a lateral flange on chaetiger 5. Moreover the palps are characterized by continuous black lines along the margins of the ciliated groove. The combined findings of this study provide compelling evidence that P. websteri is expanding its range within the Mediterranean coast. Given the potential for severe ecological and economic impacts associated with this invasive polychaete, this study serves as an urgent call to action for increased monitoring of P. websteri in both farmed and wild Pacific oysters in the Mediterranean Sea. Identification key of Mediterranean Polydora is provided.

Large aggregations of cold-water corals (CWC), often termed CWC gardens, are considered as biodiversity hotspots and recognized as vulnerable marine ecosystems. Their three-dimensional structure creates important habitat complexity, providing refuge, nursery and feeding areas for many deep-water species. Their vulnerability and limited current knowledge highlight the importance of describing the distribution and habitats of these gardens. Using remotely operated vehicles (ROV), we describe an unprecedented large aggregation of the co-occurring black (Antipathella subpinnata) and yellow (Dendrophyllia cornigera) coral gardens in the mesophotic in the northern Bay of Biscay. These distributions acknowledged their latitudinal and bathymetric distributions, in particular for A. subpinnata. Black and yellow corals presented mean densities of 2.0 {+/-} 1.8 colonies.10 m-2 and 1.5 {+/-} 1.3 colonies.10 m-2, respectively. Following the complex topography of this area, they were mostly fixed on hard substrates, particularly in narrow crests close to or surrounded by sand or mud planes. These findings are essential to develop appropriate local spatial management plans, ultimately contributing to the conservation of these vulnerable ecosystems.

Understanding fine-scale population genetic structure is essential for biodiversity conservation and evolutionary research, but conventional phylogeographic studies often face labour and financial cost constraints. This study proposes a two-step survey strategy that integrates environmental DNA (eDNA) analysis and PCR-based genome-wide SNP genotyping, aiming to evaluate its effectiveness by comprehensively characterising the population structure of widely distributed species. As a model system, we selected the odontobutid gobies, Odontobutis obscurus and O. hikimius, which occur in western Japan. Initially, water samples were collected from 335 sites across western Japan. Subsequently, tissue sampling for SNP analysis was conducted at 49 sites representing the regional groups and species. The eDNA analysis revealed two major mitochondrial clades within O. obscurus, each comprising multiple geographically distinct groups. Subsequently, tissue sampling and SNP analysis were conducted at representative sites of each regional group and species. Nuclear genomic SNP data (661 loci) corroborated the deep divergence between the two clades of O. obscurus and, unexpectedly, indicated that O. hikimius, whose range lies at their boundary, originated through hybridisation between them. Geographic patterns of the regional groups inferred from both mitochondrial and nuclear data were largely explained by historical geological events such as mountain uplift and ancient river system dynamics, and provide unprecedentedly detailed insight into the population structuring of the focal species. This study demonstrates that the integration of eDNA and SNP analyses provides a cost-effective and scalable approach for high-resolution phylogeographic surveys.

Exploring the causes of species extirpation can provide insights into mitigating the ongoing extinction. The Japanese otter Lutra lutra whiteleyi had extincted around 1970s, but their extinction causes remain unknown. To elucidate the ecological relationship among their foraging ecology, habitat degradation, and the extinction, we assessed dependency of Japanese otters on marine- or freshwater-derived resources using sulfur stable isotopes ({delta}34S: 34S/32S) of the museum specimens which were collected on the brink of extinction. Our results clearly showed that the otters strongly depended on marine-derived resources, indicating anthropogenic activities led to depletion of freshwater prey and a potential extinction factor of the last population of otters in Japan. Protecting freshwater habitats was crucial for preventing otter extinction in Japan, and for safeguarding the extant otter species.

Oceanic islands, due to their evolutionary history and isolation, hold a disproportionately high proportion of endemic species. However, their evolutionary history also makes them vulnerable to extinctions, with most known extinctions occurring on islands. Plant-animal interactions are particularly important on islands, as island systems generally have low redundancy and are more vulnerable to disruption either via extinction or by invasive species. Here, we examined the fruit removal and seed predation of a keystone palm, Caryota mitis, on the remote oceanic island of Narcondam. The island endemic Narcondam hornbill (Rhyticeros narcondami), was the sole seed disperser of the Caryota mitis (90 hours; N = 15 trees), indicating a lack of redundancy in seed dispersal of the palm on this island. While the invasive rodent, Rattus cf. tiomanicus was the sole predator of the Caryota mitis seeds in the forest (N = 15 individual fruiting palms, 416 trap nights). Overall, 17.1% of the seeds placed (N = 375 seeds) were removed. Seeds placed under and away from the canopy, and at different densities (2 plots with 10 seeds each; 1 plot with 5 seeds, respectively), showed similar removal rates. This is indicative of ambient seed predation and the lack of safe sites for the regeneration of Caryota mitis, with potential deleterious effects on the subsequent stages of the "seed dispersal cycle". Here, from a data deficient site, we provide baseline information on the plant-frugivore interaction of a keystone palm and the potential impacts by an invasive rodent.