The invasion of aquatic environments by alien fish species is an important issue in ecological research. Alien fish species, such as Ponto-Caspian gobies, can impact native communities and ecosystems through predation, competition, parasite vectors, disturbance, and habitat modification. In this study, we present new locations of monkey goby Neogobius fluviatilis in the waters of the Great Masurian Lakes system (north-eastern Poland). Four methods (Nordic gillnets, electrofishing, fishing rod, and Vulkan crayfish trap) were used for fishing. The presence of N. fluviatilis was recorded in nine lakes of different morphometry and trophic status, one canal, and at one site of the Pisa River in 2018–2020. Total length and body weight of N. fluviatilis were rather small (42–113 mm; mean of 81 ± 19 mm and 0.3–13.7 g; mean of 6.4 ± 3.6 g, respectively). The most specimens were in the range of 80 to 100 mm. Our study documented that N. fluviatilis inhabits lakes, rivers and canals. The invasion of N. fluviatilis into the Great Masurian Lakes system occurred across the Pisa River from the Narew River. In the Great Masurian Lakes, the northernmost place in the system in which N. fluviatilis was recorded was Lake Niegocin. We may expect that N. fluviatilis can quickly spread farther, reaching lakes situated in the northern basin of the system in the near future.

Specimens of webspinners found on Fuerteventura Island (one of the Canary Islands) were provisionally identified as Embia cf. savignyi Westwood, 1837 (Embioptera: Embiidae). Embia savignyi is native to northeastern Africa and the population reported from the Canary Islands is introduced. The report provides location data, photographs of specimens, a description of cytogenetic characteristics, a DNA barcode, and a description of the morphological intrapopulation variability. A morphologically based identification key for Canary Island webspinners, composed of three alien species, is also provided.

The pleustid amphipod Incisocalliope aestuarius (Watling and Maurer, 1973) was described from the North American Atlantic coast in the 1970s. In this study, the species is reported from the German North Sea for the first time. An established population was found in four different harbour locations along the coast of Lower Saxony for five consecutive years since 2016. In Europe, I. aestuarius has already been reported from France, the Netherlands and Belgium. As a member of fouling communities, the species tolerates reduced salinities and is often associated with hydroids growing on artificial hard substrates. Due to its cryptic lifestyle, as well as its challenging identification, the species has been overlooked for years. Therefore, it seems likely that I. aestuarius has already been established in more estuarine or harbour locations in Europe.

Invasive macroalgae represent a major threat to marine ecosystems worldwide. Codium fragile ssp. fragile is one of the most invasive species in the world. The species has deleterious impacts on marine ecosystems, but can also coexist with other Codium congeners, with neutral impact. Several invasive macroalgae have been described to occur along the west coast of the Iberian Peninsula, including C. fragile. However, despite its presence being noted in citizen science surveys, the occurrence of C. fragile on the coast of Portugal was not confirmed (except in the Azores Islands). The cryptic nature of this invasive macroalga has led to several misidentifications, and strict taxonomic approaches must therefore be used to confirm sightings. Previous intensive field sampling (2017–2018) aimed at recording the presence of different macroalgae did not find C. fragile along the Portuguese coast, northwards from Praia do Matadouro. Here, we report the first confirmed record of C. fragile on the coast of Portugal, in the Avencas Marine Park. Identification of the alga was confirmed by microscopic examination of the utricles. Early detection of invasive species is essential, and further research should be carried out in the surrounding areas in order to better understand the invasion pathways to enable correct application of management plans.

The Asian tapeworm Khawia japonensis, a specific parasite of the common carp (Cyprinus carpio), has been found for the first time in Europe, in Italy (2010), with further records also in Slovakia (2014) and the Czech Republic (2016). In the present paper, new data on the distribution of the non-indigenous K. japonensis is presented in different countries in Central Europe (Hungary, Poland and Slovakia), including its first record in Hungary and Poland, and in the wild fish in the Laborec River (Tisa River basin) and drainage canal of the Zemplínska šírava water reservoir, in south-eastern Slovakia. The highest prevalence (47%) was recorded in a carp breeding facility in eastern Slovakia, and the highest intensity of infection (8 parasites per fish) occurs in free-living fish from the Laborec River located in the same region. The morphology of recently found K. japonensis specimens is compared with that of population from common carp in Italy and from the same fish host in Asia and North America. The first insight on pathology, including histological examination, is provided, and pathological changes induced by the scolex of K. japonensis penetrated into the intestinal villi are also described. The recent spreading of this parasite in several major European river basins (Danube, Elbe, and Vistula) indicates its high ability to establish in new regions and represents another example of anthropogenic introduction of fish pathogens.

This paper reports on the first record of the Pacific oyster, Crassostrea gigas (Thunberg, 1793), in the southern Black Sea, based on a sample of 235 specimens collected from rocky shores 23 km west of the city of Ordu, northern Turkey. Species identification was confirmed by nucleotide sequencing of two mitochondrial gene fragments, viz. COI and 16S rRNA in five individual oysters. Analyses of mitochondrial cytochrome oxidase I (COI) sequences from southern Black Sea coastlines suggest that all samples were Pacific oyster, Crassostrea gigas. In addition, this study provides the first analysis of length-weight relationships (LWR) for C. gigas collected from the southern Black Sea. The relationship between mean shell length (SL) and mean total weight (W) was SL = 0.0143W^1.6662 (r² = 0.6589). The specimens were morphometrically characterized as follows: mean shell length (SL) 59.57 ± 13.65 mm (range: 24.09–98.17 mm), mean shell width (SWi) 28.05 ± 6.91 mm (range: 10.50–50.87 mm), mean total weight (W), 13.62 ± 5.03 g (range: 0.78–36.89 g), and mean meat weight of 1.5 ± 0.90 g (range: 0.01–5.83 g). The relationships between the morphometric parameters suggested negative allometric growth. According to the results, C. gigas has created breeding populations on the Turkish Coasts, becoming the dominant species on some hard substrate, including rocky bottoms and large rocks used as fill locally to gain more land in the coastal area.

The genus Cycas forms one of the oldest plant groups. Cycas are utilized as ornamental plants in urban gardens, so they are found in different cities’ landscapes. At present, Cycas are affected by serious infestations of Aulacaspis yasumatsui (cycad aulacaspis scale; CAS) that eventually lead to the plant’s death. Aulacaspis yasumatsui is native to Thailand and has spread in all continents as an invasive species. To determine the distribution of Aulacaspis yasumatsui in Panama, we sampled 68 sites in 24 municipalities in nine of ten provinces of the Republic of Panama. Our results suggest that Aulacaspis yasumatsui is spread in the low territories of the country; however, we did not observe CAS-infested cycads in the highlands of Panama (> 700 m). Besides the economic loss caused by the death of plants whose price in Panama ranges from tens to hundreds of dollars, Cycas serve as a food supplier to birds and bats in the trophic food web.

An overview is presented of the Non-Indigenous Species (NIS) of algae and invertebrates recorded in the marine and brackish coastal waters of Normandy in France. Out of the 152 NIS found, 86 have been introduced through shipping (ballast waters and fouling) and 66 through aquaculture activities. A total of 95 NIS are linked to a Pacific origin and 32 come from the north-western region of the Atlantic. Among the 152 NIS identified, only nine show an invasive demography in Normandy waters. The first introductions occurred in the middle of the 19^th century and became frequent by the beginning of the 20^th century. However, over 50% of the NIS so far recorded were found only during the three last decades.

The presence of Pinctada imbricata radiata (rayed pearl oyster) was explored in the Bay of Palma (Balearic Archipelago, NW Mediterranean Sea) by means of Rapid Assessment Surveys (RAS). Forty-three specimens were found in rocky substrates from recreational marinas and neighbouring natural habitats, including Cabrera National Park. Average hinge length was 26.8 ± 13.3 mm and average shell height was 28.6 ± 16.2 mm; a maximum size of 55.6 × 55.9 mm was measured. The main occurrence of the exotic oyster in marinas, and also far away in Cabrera, points to maritime transport as the primary introduction vector; whereas records in the adjacent natural habitats suggest secondary spread by natural dispersal has occurred. Considering the populations of P. imbricata radiata documented in the Balearic Archipelago, the bivalve seems to be well established in the area. The study explores the potential of RAS as early detection tools for invasive species along the coastline, and recommends further assessment on the ecological impact of P. imbricata radiata in marine protected areas.

Adenocaulon adhaerescens (Asteraceae), a native species from the Russian Far East, has escaped from cultivation in N.V. Tsitsin Main Botanical Garden of the Russian Academy of Sciences, Moscow. Herewith, we record it as a new invasive alien plant species: recently it has been recorded in 13 localities in Moscow and the surrounding area and we revisited 12 sites and confirmed its distribution at 8 localities. In populations of Adenocaulon adhaerescens along trails in parks and recreational forests its covering could reach 100% (recorded in Moscow and Moscow Region). The biggest plants produce more than 5000 seeds per season and these are equipped with viscid glands. Those glands make seed distribution over great distances (both via anthropo- and zoochory) very effective. Unaided or unintentional introduction of this species in East European countries and its further invasion in natural plant communities is likely to occur, so monitoring of the initial populations of this species and implementing measures intended to prevent its spread are necessary.

Invasive plants have caused significant negative ecological and economic impacts throughout the world. Parrot’s feather (Myriophyllum aquaticum) is an aquatic plant introduced from South America to South Africa, USA, Europe, New Zealand through the aquarium trade. It was recently brought to China where naturalized populations have become widespread. However, there is little information about the status, distribution, and the ecological and economic impacts of parrot’s feather which is critical to the Chinese government and environmental managers. We summarized introduction pathway, current distribution, and ecological impacts of parrot’s feather by field investigations and literature review. Our study could provide significant references for the management of non-native aquatic plants in China.

Freshwater organisms are facing rapid population declines and substantial extinction risks, and invasive species represent one of the significant drivers of freshwater biodiversity declines. Aquaculture practices and trade activities in China are expansive, and the establishment of nonnative freshwater species is widespread. The red-eared slider Trachemys scripta elegans (Wied, 1838) is one of the world’s worst invasive species, and this species is traded nationally both in food and pet markets in China. Red-eared sliders had entered native ecosystems through escapes and intentional releases in China. However, investigations mostly have focused on eastern and central China. Here, we present results of a field survey reporting a new distribution of red-eared sliders on the Qinghai-Tibetan Plateau, which is a conservation priority area located in western China. Forty-one individuals in three plots were observed in 2019 and 2020. Four individuals were captured, and no individual was sexually mature. The average carapace length and body weight of the specimens were 70.57 (± 13.071) mm and 50.70 (± 8.087) g, respectively. Red-eared sliders might negatively influence biodiversity since there are no native testudine species in this region. Thus, we suggest putting more effort into monitoring red-eared sliders and other nonnative species, discouraging unscientific animal release, and emphasizing the threat of releasing nonnative species to the public.

The first records of Trypauchen vagina (Bloch and Schneider, 1801) from Mediterranean Egyptian waters and of Rachycentron canadum (Linnaeus, 1766) from Libyan waters are hereby described, providing new information on the expansion of these two Lessepsian fishes along the southern Mediterranean coasts lying to the west of the Suez Canal. The finding of another Lessepsian fish, Platycephalus indicus (Linnaeus, 1758) from a region further west of its previously-known introduced distribution within Egyptian Mediterranean waters, is also reported, indicating an ongoing successful establishment of this species, previously considered uncommon within the same waters.

We present the second edition of the checklist of alien orthopterans (Orthoptera) and mantises (Mantodea) in Austria. In total, 17 alien Orthoptera and three Mantodea species are reported, of which eight Orthoptera species are established, while nine are casual. All three mantises are casuals. In comparison to the first checklist of alien Othoptera and Mantodea species for Austria published in 2002, the number of alien Orthoptera and Mantodea has risen by 14 species. Most alien Orthoptera and Mantodea in Austria are native to other parts of Europe. Most invaded ecosystems in Austria are man-made habitats, and heated environments such as buildings and greenhouses. No species is currently known to cause any negative environmental or socio-economic impacts.

Distribution range of a large tropical millipede Chondrodesmus cf. riparius Carl, 1914 has been continuously expanding in Europe over the last two decades. Since the first records in 2000 in North Sweden this Colombian species has become well established in flowerpot habitats of Europe. The way of its spreading is traceable in published records, and points to Sweden as the country to which this species was introduced. Records are scattered, therefore the distribution revealed here might be underestimated. It is expected that this species will expand throughout Europe in consequence of intensive international plant trade. Herein, the first records of this alien millipede in flower pots in Poland are presented and the current range in Europe is summarized. The SEM images of the gonopods, and a partial COI mtDNA sequence (DNA barcode) are included.

The first mass occurrence of the alien, tube building polychaete Ficopomatus enigmaticus (Fauvel, 1923) was found in the Baltic Sea in 2020. Detailed surveys of private marinas, yacht clubs and boats as well as visual inspections, scratch sampling and a camera assisted remotely operated vehicle revealed its occurrence along a 12 km stretch of the lower saline section (7.12–11.67 PSU) of the Warnow River Estuary, Germany in the western Baltic Sea. The species was found mostly in sheltered areas in 1.0–4.5 m water depth, but it was not found in the higher saline areas (14.10–15.31 PSU) of the estuary or along the coast. Colony densities up to 28,800 ind. m^-2 were detected. The occurrence of the invasive F. enigmaticus has the potential to alter the ecosystem significantly, suggesting that the colony be monitored closely for signs of expansion, establishment and possible alterations to these ecosystems.

Pontederia cordata L. (Pontederiaceae) is an emerging aquatic plant native to the American continent that has been introduced to various continents through long-distance commerce as an ornamental plant. Individuals growing in the wild belonging to Pontederia L. genus where found in South Spain. The analysis of diagnostic characters of the collected specimens and their comparison to those represented in herbarium vouchers allowed us to distinguish them from its closest relative, P. sagittata C. Presl and to assign all the specimens found at the locality to P. cordata L. This is the southernmost European record of the species. It was clear that the origin of the introduction was the use as ornamental aquatic plant in the area. Its invasion risk was assessed for Europe, firstly, by analysing the suitability of European climate for the species, secondly, by assessing the potential impact. Results showed that from 92.5 to 92.9% of the meteorological stations analysed showed climate conditions that were compatible with the species’ climatic requirements. The ecological characteristics of the species and the climatic features of the area analysed suggest a great risk of invasion that could lead to the species’ spread in Europe. These findings suggest that P. cordata could threaten European wetlands.

I report here the first record of Heptapleurum arboricola Hayata (syn. Schefflera arboricola (Hayata) Merr.) (Araliaceae) as a casual non-native plant throughout the Mediterranean area. I observed the natural regeneration in urban areas at Castellammare del Golfo, a small coastal town in north-west Sicily (Mediterranean Italy). Due to the lack of self-sustaining populations and the short-term observational period, Heptapleurum arboricola should be considered as a casual species according to the classification of non-native plants. The detection of early signs of naturalization of non-native plants is of crucial importance for the management and control of invasive species. The main abiotic and biotic factors involved in the possible future spread of the species are briefly discussed.

Natural infection of non-native brown bullhead catfish Ameiurus nebulosus Lesueur, 1819 (Siluriformes: Ictaluridae) with larvae of the cestode parasite Ophiotaenia europaea Odening, 1963 (Onchoproteocephalidea) was confirmed at several localities in the Czech Republic, this representing the first record of O. europaea larvae in the country. Adult cestodes infect the intestinal tract of colubrid snakes [predominantly grass snakes Natrix natrix (Linnaeus, 1758) and dice snakes Natrix tessellata (Laurenti, 1768)], with cyclopoid copepods and fish and/or frogs as the first and second intermediate hosts, respectively. Brown bullhead was introduced to Europe from North America during the last century and has since become widely distributed in many European countries. Larval cestodes were found encysted in the brown bullhead mesentery and on the surface of the intestine and kidney; all parasites were alive. Species identification was confirmed using sequencing of partial 18S and 28S rDNA and COX1 mtDNA. Brown bullhead are only the second natural intermediate/paratenic host of O. europaea reported, and the first confirmed by molecular genetics. Its wide distribution within different populations of A. nebulosus indicates that this non-native fish species has been successfully included into the life cycle of O. europaea. Dice snakes, one of the two natural definitive hosts of O. europaea, are rare in the Czech Republic and classified as an endangered species; and larvae of O. europaea were predominantly found in localities close to the distribution area of this snake species. Possible impacts of bullhead catfish introduction into regions with dice snakes are discussed further.

We confirm the presence of the Indo-West Pacific barnacle Amphibalanus amphitrite (Darwin, 1854) in Chile, based on the discovery of a population in Tongoy estuary in northern-central Chile, and following upon an obscure report of its presence in Chile as of 1980 at unidentified sites.

The narrow-clawed crayfish Pontastacus leptodactylus is known as a species expanding their range in northern areas of the Europe. This study aims to present new records, check the previously knows sites of P. leptodactylus records in the northwestern region of Russia (Karelia, Murmansk, and Arkhangelsk regions), and discuss possible reasons for its current range extension to the north and disappearance in southern locations of this region. Twenty years ago, the northern border of the P. leptodactylus range run from southern Finland to the east-north of Lake Ladoga, skirting to the north of Lake Onego, and further east to the Northern Dvina. To date, it disappeared widely from northern lakes and rivers being recorded only in 25% of previously known locations (mainly in southern Karelia), where this species was introduced and established in the 1920s–1970s. At the same time, during the last decade, P. leptodactylus was recorded more northern, in lakes at White Sea costs. Considering that some of the new sites of P. leptodactylus are located in uninhabited by humans areas, the reason due to which this crayfish extends its range close to the Arctic areas may be its natural dispersal. Local climate warming might also facilitate the successful adaptation and establishment of this species there.

Aquarium trade constitutes an important pathway for the introduction of non-indigenous aquatic organisms in several parts of the world. Here, based on a series of observations carried out along the Lebanese coasts, we document the first record of four non-indigenous fish species in the Mediterranean Sea. The paper discusses their occurrence as releases from home aquaria as the most plausible mean of introduction.

Freshwater turtles have been introduced to a diversity of environments worldwide, sometimes leading to devastating impacts on native biodiversity and ecosystems. Documentation of species and distribution of non-native turtles is needed to effectively manage potentially invasive turtles. Here, we compiled a species list and distribution map of non-native turtles found in Hong Kong by combining field survey data, anecdotal records made by naturalists, and citizen science data. We collected 96 records, involving 25 pure species and three putative hybrids distributed widely throughout Hong Kong. The red-eared slider (Trachemys scripta elegans), listed as one of the world’s 100 worst invasive alien species, was the most frequently recorded species. Most, if not all, non-native turtles were probably released intentionally, as abandoned pets or in religious release. We urge for strengthening legal regulation and developing measures to stop intentional release, particularly religious release.

The occurrence of the alien earwig Euborellia femoralis (Dohrn, 1863), which is native to Asia, is reported for the first time in Europe. The species was found at two sites (Rhodes and Magnesia) in Greece in 2017–2020. The identity of morphologically identified specimens was verified by comparison of COI barcodes, and a phylogenetic tree for Euborellia species was constructed with available COI sequences. In addition to the typical fully winged specimens of E. femoralis, the apterous forms of both sexes are reported. A morphology-based identification key for European Euborellia is provided; the key considers both winged and apterous forms of E. annulipes and E. femoralis.

The sex ratio, size at first maturity, morphological variations and abundance of the invasive species Blackfordia virginica, were analysed in the lagoon of Pueblo Viejo. Zooplankton were collected with a 505 µm net throughout the lagoon during October and December 1992, March, April, June and August 1993, and March 2009. Data were recorded simultaneously for salinity and temperature. A female/male sex ratio of 0.95:1.00 and a minimum size of gonadic maturity of X= 5.25 ± 0.17 mm umbrella diameter were recorded. Blackfordia virginica presented 33 types of morphological variations. The number of marginal tentacles (53–104) increased with size (2.5–13.0 mm). Medusae were collected in this lagoon only in March and April 1993, with average densities of 1,946.75 and 2,508.83 ind/100 m³ respectively. These medusae were recorded at temperatures of 19.0–28.0 °C and salinities of 11.0–21.0 PSU. The density of B. virginica was highly correlated with salinity (r_s = 0.796, n = 114, P < 0.001). The high density of specimens, the wide range of sizes, and the presence of both mature females and males as juveniles indicate that this species can reproduce and develop in this lagoon system. The absence of medusae in March 2009 indicates that the species is not a resident in the system in response to the oligohaline conditions (0.0–7.0 PSU) that are characteristic during June to October.

Alborán is a small volcanic island located in the center of the Alborán Sea, W Mediterranean, 85 km from the Iberian Peninsula (Europe) and 55.5 km from the NW African coast line. Despite its small size (605 × 265 m), four distinct exotic lizard species have already been reported there, one of them presumably extinct (Saurodactylus mauritanicus). Throughout history, the island has maintained an intermittent human presence, being now permanently occupied by a military detachment connected to the Iberian Peninsula mainly by means of cargo shipments. Hence, this communication between the island and the continent has fuelled human-mediated species introductions. Populations of the geckos Tarentola mauritanica and Hemidactylus turcicus and the most recently reported wall lizard Podarcis vaucheri still remain in the island. Here, we used molecular tools to assess species identity and putative invasion pathways. As expected, results confirm the initial species assignement and indicate southern Iberia as the source area. However, surprisingly, two clades of T. mauritanica were found, the European clade commonly introduced elsewhere, and the Iberian clade, reported here for the first time outside its native distribution. Moreover, the reported southern Iberian lineage of P. vaucheri in Alborán, represents the third case of introduction of this species. This amazing concentration of alien species in such a reduced territory highlights how prone small islands are to be sucessfully invaded, and that these should not be neglected in invasion biology. The effects of these alien reptile species over native taxa are yet unknown, although an impact over several endemic invertebrates cannot be ruled out. As such, regular monitoring should be implemented to prevent they act as hubs for future new introductions.

Since the first report of the box tree moth, Cydalima perspectalis (Walker, 1859) (Lepidoptera: Crambidae) in northern Greece in 2013, the pest has gradually expanded its range to a total of eight administrative regions in the country. A survey consisting mainly of citizen science occurrence records provides a new insight on the distribution of the box tree moth in Greece. The data collected circumscribe invasion into boxwood Buxus sempervirens L. stands, especially at Mt Olympus National Park. The updated invasive status and the ecological risks are discussed with particular reference to the Natura 2000 area in Mt Olympus.