Weedy sunflowers can cause severe yield losses and have recently been reported in several regions of Europe. We present the results of a survey of 24 grid cells 1 km² in size on the distribution of weedy sunflowers in two different regions in Austria. Our results showed that weedy sunflowers (Helianthus annuus L.) occur in various crops (oil pumpkin, soybean, and maize). While most occurrences were small, a few fields were heavily infested (> 500 individuals) and weedy sunflowers reached cover values of up to 25%. The average number was 175 plants/km² across all grid cells surveyed, with an average of 324 plants/km² in the 13 infested grid cells and a maximum of approx. 1000 plants in the most heavily infested grid cell. The expression of recorded morphological traits (i.e., head number, height, and head diameter) varied considerably between populations of weedy sunflower, escaped sunflower, and cultivated sunflower. This study is the first to assess the infestation of weedy sunflowers in fields in Austria. We found evidence of the potentially substantial impact of weedy sunflowers on crop yields. Our findings highlight the need for further monitoring and controlling of weedy sunflowers in fields.

Klasea quinquefolia (M.Bieb. ex Willd.) Greuter & Wagenitz is a perennial and rhizomatous herb native to the Russian Caucasus, Armenia, Azerbaijan, Georgia, Iran, and Asian Turkey. The natural habitats of the species are deciduous forests or open areas in hill/mountain areas. Outside the native range, the species is mainly known for its ethnobotanical and pharmaceutical uses but in recent years, it has been also recorded as an alien species in Austria. In this work, we reported the first occurrence of K. quinquefolia in Italy. The species was recorded in August 2023 in the Monza Park (Lombardy, N-Italy) in a mesophilous woodland dominated by Carpinus betulus. The new population was subdivided in 10 subpopulations distributed in habitat patches with surface areas ranging from 0.085 to 95,008 m². The total population accounted almost 500 individuals with a flowering population size of about 350 individuals. Likely, the establishment of K. quinquefolia is linked to the presence of internationally frequented facilities that might have favoured its unintentional arrival (e.g. the Monza Racetrack) or to historical reasons of past introductions to Royal Gardens of the Monza Palace. Presently, it should be treated as a naturalized alien species in Italy even if its further spreading could be favoured by the species’ habitat preference and climate change.

Carex pilulifera L., a perennial herb native to Europe, was recently introduced and found in subalpine vegetation of Reunion Island. In this study, we assessed the current distribution and cover of C. pilulifera within the subalpine vegetation (Piton des Neiges and Piton de la Fournaise) of the National Park of Reunion. We used GLM models to analyse relationships between C. pilulifera and habitat, disturbance type, and proximity to fodder and grazing areas. We evaluated the potential distribution of C. pilulifera using species distribution models. Presence of C. pilulifera was only found on Piton de la Fournaise with a mean cover of 16.6% (where present). Carex pilulifera was the fourth most observed alien species (27% of all observations). According to the SDM, it could also occur in Piton des Neiges but was not found. Carex pilulifera was significatively more present in subalpine grasslands and close to grazing and fodder areas. We believed fodder and grazing areas to be the introduction pathways of this species. This study confirmed the status of C. pilulifera as an invasive species in the subalpine vegetation of Reunion Island which comprises a high level of plant endemism. We suggest that management should primarily focus on surveying potentially suitable areas in Piton des Neiges to eradicate new introduction and to control the species within high biodiversity areas in Piton de la Fournaise.

The Asian or yellow-legged hornet Vespa velutina nigrithorax has been accidentally introduced into several European countries. This invasive species has an impact on entomofauna and plant biodiversity through reduction of pollinators as well as affects apiculture. We present the first record of the species in the Czech Republic, notes associated with this record, its COI barcode, and modelled potential distribution. A specimen of Vespa velutina nigrithorax was recorded in October 2023 in Pilsen city (West Bohemia, Czech Republic). The nest was traced by observing released individuals, detected on Black locust (Robinia pseudoacacia), and removed. The COI barcode confirmed the European origin of this nest. The species either followed natural routes from Bavaria (Germany) or was introduced by transportation. A species distribution model (Maxent) trained on European distribution showed that the western Czech Republic is more suitable for the species than its eastern parts, as the species likely prefers lower continentality. During 2024, Vespa velutina nigrithorax was also recorded in Hrádek u Rokycan (West Bohemia, Czech Republic). Recently, these records represented an isolated occurrence in the Czech Republic; however further expansion of this invasive species is expected.

In 2023, the invasive black twig borer Xylosandrus compactus (Eichhoff, 1875) (Coleoptera: Scolytinae) was found for the first time in Switzerland. Outbreaks of this non-native species have been recorded during phytosanitary survey activities in four municipalities south of the Alps in the Canton of Ticino. Conducting genetic analyses using the mitochondrial COI barcode region, specimens found in Switzerland were identical with those from France, Italy, and Spain, suggesting a European source of invasion. So far, only ornamental plants in urban areas were found to be affected by attacks of X. compactus. However, because of the increasing proportion of broadleaved evergreen plant species, the availability of suitable host plants such as Laurus nobilis may also favour the spread of X. compactus into insubric forest systems. Three previously undescribed host plant species, Argyrocytisus battandieri, Mahonia aquifolium, and Wisteria sp., were identified. In addition, fungal isolations from adult beetles and breeding galleries revealed eight fungal species likely or potentially associated with X. compactus. These include Ambrosiella xylebori (Ascomycota: Ceratocystidaceae), the obligate ambrosia fungus of X. compactus, and a Thyridium species (Ascomycota: Thyridiaceae) that has been found as an associated fungus in previous studies.

Invasive species are a growing global concern. Modern transportation and the pet trade are facilitating the spread of invasive species. In particular, the global trade of freshwater turtles remains prevalent, with a significant emphasis on their utilization as pets. Aligning with other parts of the world, many recent studies reported a number of alien turtle species in the wild in Korea. However, knowledge of their local establishment and natural breeding is still very limited. In the current study, we report the first natural breeding of Mauremys sinensis in the wild in South Korea. The external features of the observed individual and egg characteristics confirmed its identification. The individual took around 70 minutes to build the nest, lay eggs, and cover up the nest with the soil that it dug from the nest. We recorded a clutch size of ten eggs. The rigid-shelled eggs had an average elongation of 1.82 mm, smaller than M. reevesii. Thus, we confirm the natural breeding and local establishment of M. sinensis in South Korea. Considering previous reports, this finding is significant for understanding both potential competition and putative hybridization with the native species, especially M. reevesii, the endangered native freshwater turtle species in Korea.

The razor-backed musk turtle (Sternotherus carinatus) is native to the Southwestern United States and is traded as a pet. Currently, turtle species that are traded as pets have been observed in the wild with increasing frequency, and S. carinatus is among them. To effectively manage an invasive species, it is necessary to know its distribution. Therefore, in this study, we report a new observation of S. carinatus. We captured the turtle in a reservoir in Gwangju, South Korea, and confirmed it to be S. carinatus through morphological characteristics and genetic analysis. Our results show that, despite extensive efforts in the management of invasive species, species traded as pets continue to be observed in the wild.

Due to the environmental and economic costs caused by invasive bird species, it is crucial to document their initial stages of invasion and manage them before control efforts become unfeasible. In this study, we conducted extensive sampling in search of the African collared dove (Streptopelia roseogrisea) in three regions of Mexico: The Northwest, “El Bajío” (central Mexico), and the Southeast. We documented five records of this species in two northwestern states (Sonora and Baja California) and analyzed additional sightings from citizen science and scientific literature to evaluate its presence and geographic distribution in Mexico. Streptopelia roseogrisea has been reported in nine Mexican states (32 records), with its first record occurring in 2000 in Tijuana, Baja California. The species is invading Mexico on two fronts: from populations established in the southern United States expanding southwards into northern Mexico, and individuals escaped/released from captivity invading central Mexico. Additionally, we used temperature and precipitation data to determine its climatic niche in Mexico. We compared it with the climatic niches of the United States populations and with the climatic space of its original distribution range in Africa and the Arabian Peninsula. We found that the climatic niche of the Mexico and the Southern United States populations is similar, and did not overlap with the climatic space present in its original geographic distribution. This suggests that niche models based on the climate of its original distribution could fail to predict the invasibility of this species in North America. Although S. roseogrisea does not seem to constitute a high-risk invader, it is important to document its early invasion process and take action before it spreads throughout the country, as it recently happened with the Eurasian collared-dove (S. decaocto).

Invasive species, particularly omnivorous rodents, have damaged island ecosystems around the world. The unique flora and fauna of island systems have typically not evolved with omnivorous rodents and are heavily impacted by their introduction. Wake Atoll of the southern Pacific Ocean is a 707-hectare coral island complex of three islands managed by the U.S. Department of Defense (DoD). DoD restricts civilian access to the atoll but aircraft and seacraft regularly visit the island to transport military equipment and to sustain the year-round military and contractor personnel stationed on the atoll. Wake Atoll had been invaded by Rattus rattus complex rats and R. exulans (Pacific rats). A 2012 eradication effort successfully removed the larger-bodied R. rattus complex species but the smaller-bodied R. exulans escaped eradication and continue to be numerous. During routine small mammal monitoring in February 2022, two individuals of another species of rodent were discovered and in August 2022 a pregnant female of this larger-bodied species was captured. Here, we report the mitochondrial DNA-based identification of the three individuals discovered on Wake Atoll in 2022. Based on mtDNA, we were able to ascertain that these individuals are likely Neotoma albigula, a species whose native range is restricted to the south-central United States and Mexico. All three Wake Atoll specimens shared the same mtDNA haplotype, which had 99–100% sequence similarity to several N. albigula specimens collected in south-central New Mexico. We propose that one or more live N. albigula may have been transported from one of the active military bases that routinely supply operations conducted on Wake Island. This work highlights that novel invasive species are an ongoing problem and can arise from species not formerly known to be invasive. Further, management of this problem must focus on biosecurity efforts to reduce the probability of novel or recurring invasions.

Here, we provide an overview on Reeves’ muntjac (Muntiacus reevesi) in Austria, a deer species originating from southeastern China and introduced to Europe at the end of the 19th century. Muntiacus reevesi is currently established in several countries of the European mainland and the British Isles, and was included in the list of invasive alien species of Union concern, due to its potential detrimental impacts, such as feeding damage, competition, and car accidents. In Austria three confirmed observations of Reeves’ muntjac in the wild were reported, in the federal states Salzburg, Upper Austria and Styria. All observations were made between 2016 and 2022 and were of single individuals that had likely escaped from captivity. Most recently, in April 2022 in Upper Austria a male individual has been observed for several days and was captured thereafter. Although to date there is no evidence of persistent populations in the wild, we argue that future establishment of the species in Austria is possible due to several factors. Those include the ongoing spread of Reeves’ muntjac in several countries of the European mainland, its elusive lifestyle and low detectability in initial invasion stages, as well as its ability to thrive from very small founding populations. In the light of the precautionary principle, we advocate for careful monitoring and rapid reaction while still feasible.

We report the arrival of the globally invading bryozoan Watersipora subtorquata (d’Orbigny, 1852) on remote oceanic Rapa Nui (Easter Island). Several colonies of this bryozoan were found in 2023 on artificial settlement plates in Caleta Hanga Piko, located next to the island’s anchorage site for cruise and cargo ships. The species was most likely introduced via hull fouling on internationally travelling vessels, including yachts and sailing boats. It is unknown if or how far it has spread along the island. We present an updated global distribution map for the species and discuss possible vectors of secondary dispersal, such as local boats and floating plastic litter. Moreover, we suggest prevention measures and highlight the need for monitoring and screening for this species, which may have a high potential for spreading and impacting coastal communities along Rapa Nui’s shores.

The invasive colonial tunicate, Didemnum vexillum Kott, 2022 was initially observed in Atlantic Canada in Nova Scotia in 2013 and has since been expected to spread to the western side of the Canadian Bay of Fundy due to colonies known to be present in nearby Eastport, Maine. Since 2018, we collected water environmental DNA (eDNA) samples at eight sites in the Quoddy Region in the western side of the Canadian Bay of Fundy. In 2021 and 2022 we used diver-based visual surveys and sample collection, as well as a surface-deployed near-seafloor optical imaging system to document the presence and extent of D. vexillum in the Head Harbour/West Isles/Passages Ecologically and Biologically Significant Area (EBSA) within the Quoddy Region. Forty-one dive sites were surveyed via SCUBA, and seven near-seafloor camera transects were conducted at depths deeper than dive limits (~ 30 m), collecting continuous high-definition video and periodic high-resolution still images. Didemnum vexillum was detected at two sites from eDNA metabarcoding and quantitative PCR in 2018, 2020 and 2021, and observed by divers at 11 sites, two of which exhibited extensive tunicate coverage. Of the 1945 m² area surveyed by the near-seafloor drift camera system, D. vexillum occurred at depths to 118 m and across a spatial extent of 858 m², of which 170 m² contained numerous tunicate patches and/or a homogenous mat. Didemnum vexillum was observed extensively overgrowing benthic substrates and fauna, possibly threatening the diversity of natural benthic habitats in the EBSA and adjacent areas supporting numerous commercial fisheries. This study is the first to report D. vexillum presence in the Canadian western Bay of Fundy, and the first to observe colonies at depths exceeding previous records of 81 m. We conclude by providing advice on how to improve coastal invasive species surveys from the combination of biodiversity metrics.

The tube-building bamboo worm Clymenella torquata is native to the northwest Atlantic and occurs on the east coast of North America from Newfoundland to the Gulf of Mexico. Here, we present the first records of this species in the German Wadden Sea. In October 2021, abundances of 7 individuals per 0.1 m² were recorded for the first time in the Hörnum Deep tidal basin (North Frisian Wadden Sea). In 2022, monitoring activities revealed a significant increase in abundances (214 individuals per 0.1 m²) indicating a reproducing population. Morphological and molecular methods confirmed the identity of the polychaete as C. torquata. The path of introduction of C. torquata into German waters cannot be tracked comprehensively. The species was most likely introduced via Pacific oyster (Magallana gigas) transfer for aquaculture purposes or transfer by hull fouling oysters.

The non-indigenous mysid Neomysis americana (S.I. Smith, 1873) is reported here, for the first time, along the Bay of Biscay in the Loire estuary, France in 2021. This species, originating from North-American estuaries, was initially discovered in Europe in 2010 (Wadden Sea) and first reported in France in 2017 (Seine estuary). The absence of long-term monitoring makes it impossible to know precisely the arrival of this non-indigenous species in the Loire estuary. However, this species is present in high abundance, suggesting an arrival prior to 2021. Its introduction might even be prior to or concomitant to the Seine estuary discovery, suggesting an introduction via the ballast water of the commercial vessels.

This study reports the presence of Percnon gibbesi in the North Adriatic Sea, specifically at Cape Kamenjak, Croatia. The species was first observed in the Mediterranean in 1999, and has rapidly proliferated across the region, with Cape Kamenjak now representing its northernmost finding. Seven individuals were identified during free-diving activities in Pinižule Bay in December 2023. Follow-up surveys in January 2024 revealed their presence approximately 15 meters from the shore, under large boulders, at depths ranging from 2.6 to 3.6 meters, with water temperatures ranging from 13 to 15 °C. Morphological examinations confirmed the specimen as male P. gibbesi, with a carapace length of 15 mm, carapace width of 14.3 mm, and a weight of 1.87 g. Shipping was identified as a primary vector of introduction due to the proximity of Cape Kamenjak to major Mediterranean ports. This research provides insights into the invasion dynamics of P. gibbesi in the northern Adriatic, urging proactive management strategies and collaborative efforts in monitoring programs.

The first occurrence of Lagocephalus guentheri in Maltese waters is validated through morphological and molecular analysis of a specimen collected in 2023. This non-indigenous tetraodontid entered into the Mediterranean from the Red Sea via the Suez Canal and has established itself in the Levantine basin. The finding represents a first indication of L. guentheri westward expansion toward the Malta-Sicily Channel within the central sector of the Mediterranean Sea.

Non-native aquatic plants are regarded as serious threats to aquatic biodiversity and ecosystem health. Large-flowered, or Brazilian waterweed (Egeria densa Planchon, 1849) is a submerged aquatic plant native to South America that has been introduced to all continents except Antarctica primarily because of its popularity in the aquarium trade. E. densa was brought into China after 2000, and it has become one of the most popular aquatic plants used in China’s burgeoning aquarium trade. It is one of many non-native aquatic species whose plasticity and thermal tolerance have buffered them from global warming impacts. This has allowed the establishment of feral populations that have caused significant negative impacts in China. Information about introduction pathways, distribution, and the ecological impacts of non-native species, such as E. densa has been very limited in China. This knowledge gap has hindered their effective management. Here we provide an updated distribution of E. densa in China from summarized literature data and our comprehensive field study. Furthermore, an overview of ecological impacts, and control or eradication approaches that have been used to manage and curtail the spread of large-flowered waterweed is presented.

The golden mussel Limnoperna fortunei is native to Southeast Asia but is now widespread in South America. Limnoperna fortunei is an ecosystem engineer able to change the environment, and also directly affect the native species. Golden mussel grows attached to hard natural and artificial substrata in dense agglomerates, up to 150,000 ind m^-2. The main goal of this paper is to report the invasion of the golden mussel Limnoperna fortunei in the Paraíba do Sul River (southeast Brazil), with emphasis on its major introduction vectors and pathways. In addition, the potential ecological and economic consequences of golden mussel spread across this river basin were also addressed. Our study reports the occurrence of the golden mussel in Santa Branca Reservoir (São Paulo, Brazil), inserted in the Paraíba do Sul River basin. This basin is important to agriculture and industrial activities, as well as water supply, for several municipalities across the basin. Moreover, this basin is responsible for a large part of the water used in the Metropolitan area of Rio de Janeiro, where live more than eight million people. The spread of this species throughout this basin may have disastrous consequences for native fauna and humans that depend on the Paraíba do Sul waters.

We report first records of the cambarid crayfish Procambarus clarkii (Girard, 1852) in Nova Scotia, Canada. This species is native to northern Mexico and the southern United States and has been introduced to all continents except Australia and Antarctica. An established population of P. clarkii was found concentrated in one area of Three Mile Lake, a small freshwater lake in Halifax County, which builds upon existing evidence that this “warm-water” species can establish in cold temperate regions. We discuss possible introduction mechanisms and impacts, as well as potential measures to better prevent and detect future invasions of freshwater species in Nova Scotia.

The red swamp crayfish Procambarus clarkii is one of the most prominent invasive crayfish species in Europe. Here, we document the first recording of this species in Slovakia, including evidence of its occurrence in two natural localities, both fed by thermal springs. The first locality is near Turčianske Teplice in Central Slovakia, immediately downstream of a commercial culturing facility for aquatic ornamentals, while the other is located approximately 150 km southwards, close to Komárno. Both P. clarkii populations are well-established, with numerous individuals of both sexes, size classes, and ovigerous females. Although none of the 32 screened adult crayfish of either population tested positive for Aphanomyces astaci, the causative agent of the crayfish plague, its presence cannot be entirely excluded. So far, P. clarkii is confined to short stretches in both sites. However, its independent expansion into nearby watercourses can be expected. Despite the translocation of non-native species of Union concern, such as P. clarkii, being strictly forbidden, illegal human actions can facilitate their dispersal. Given the still relatively limited territory conquered by the invasive species in the two localities, urgent eradication and control measures were recently adopted. The ongoing eradication campaigns yielded thousands of P. clarkii individuals extracted from both localities in 2023. As thermal springs and thermally polluted waters are known hotspots of non-native and potentially invasive species, monitoring these sites is highly recommended.