The freshwater gammarid, Crangonyx floridanus, originates from North America but has invaded and subsequently spread rapidly throughout Japan. We provide here the first genetic and microscopic evidence that C. floridanus has now also reached the United Kingdom. We found this species in two locations separated by more than 200 km (Lake Windermere in the North of the UK and Smestow Brook, West Midlands). The current distribution of C. floridanus is currently unknown, however, both sites are well connected to other river and canal systems. Therefore, the chance of further spread is high. Genetic analyses of C. floridanus indicate that British inland waters are colonised by the same lineage, which invaded Japan. We recommend further work to assess the distribution of this species and its impact on the local fauna and flora.

Sardinian herpetofauna represent a valuable biodiversity resource in the Mediterranean Basin. Among amphibians, most of the taxa are indeed endemic to the island. In contrast, water frogs of the Pelophylax genus are considered allochthonous to Sardinia, and are traditionally assigned to the Italian pool frog (P. bergeri) and its hybridogenetic hybrid (P. kl. hispanicus). Members of this genus were recently found in certain sites in northern and southern Sardinia, and ascribed to the “ridibundus” group (the “Marsh frog” species complex). As the absence of clear phenotypic diagnostic features complicates the identification of distinct Pelophylax species, particularly European P. ridibundus, P. kurtmuelleri and several still undescribed “bedriagae” taxa, an informative diagnostic mitochondrial marker (ND3) was isolated in this work in order to detect the occurrence of distinct lineages in alien Sardinian populations. As water frogs are known to readily hybridize in the wild, two further diagnostic nuclear markers (SAI-1 and 4 microsatellite loci) were subsequently screened in order to exclude the occurrence of hybrid genotypes. According to our results, three distinct taxa were detected on the island, and assigned to P. kurtmuelleri (the Balkan frog), and two cryptic taxa of the “bedriagae” group. Nuclear markers only successfully amplified alleles diagnostic for the “ridibundus”-type (R) genome. Accordingly, we can exclude hybridization with the Italian pool frog already introduced on the island, although further studies are needed to better address the occurrence of new hybrid lineages stemming from the cross between the taxa detected in this work. As eggs and tadpoles have been detected in the field, alien populations can thus be considered successfully established in Sardinia. Our study revealed for the first time the occurrence of the alien Balkan frog in the western Mediterranean. It is worthy of note that this taxon shows a high invasion potential in mainland Europe. The establishment of alien Pelophylax populations in Sardinia may be favored by vacant niches. Nonetheless, the dry hot season could limit their expansion along rivers.

Alien marsh frogs were found during bioacoustic surveys in the Aspromonte National Park, southern Italy, during spring 2015. This is to date the southernmost finding of non-native water frogs in the Italian Peninsula. Subsequent genetic characterization clearly identified these non-native frogs as belonging to Pelophylax kurtmuelleri, a species of the Pelophylax ridibundus species group. Phylogenetic comparisons with previously published sequence data placed the collected samples in a cluster of P. kurtmuelleri individuals from southwest coastal areas of the Balkans. We collected further information on this introduction by interviewing local people, and by extending bioacoustic and genetic surveys to all the potential breeding sites in the area during springtime, from 2016 to 2018. Interviews revealed that a small group of Balkan people established in the area in the early ‘80s, suggesting that marsh frogs were introduced as a food source (frog leg consumption). We found non-native frogs at eight sites, located 10 km at most from the supposed area of introduction. Considering i) the invasive potential of marsh frogs, and the associated threats to native species, ii) their still limited spread in the study area, and iii) the presence in this area of a unique evolutionary lineage of native water frogs, P. lessonae, we urge for timely management and eradication actions of this alien frog in the area, aimed at preventing its further spread and consequent negative impact on native frogs and other components of the biological community.

Globally, geckos (Gekkonidae) are one of the most successful reptile families for exotic species. With the exception of the widespread invader, Hemidactylus mabouia, however, introductions of exotic gecko species are a more recent occurrence in the Caribbean islands despite extensive introductions of exotic geckos in the surrounding Caribbean region. Here we report three new exotic gecko species establishments on the mid-sized Caribbean island of Curaçao (Leeward Antilles). Of the three new exotic species, the mourning gecko, Lepidodactylus lugubris (Duméril and Bibron, 1836) has the largest distribution on Curaçao and has likely been established for the longest time. The common house gecko, Hemidactylus frenatus (in Duméril, 1836) has a limited distribution and was likely a more recent introduction. Finally, the Tokay gecko, Gekko gecko (Linnaeus, 1758), escaped from captivity and is known from a single locality. Both L. lugubris and H. frenatus have had widespread distributions in the greater Caribbean region for over 70 years yet have only been reported from Caribbean islands within the past decade. Comparatively, the scope of G. gecko introductions on Caribbean islands is similar to L. lugubris and H. frenatus but introduced populations of G. gecko in the greater Caribbean region are virtually absent. These patterns indicate that different introduction pathways (intentional vs passive) may affect the size of exotic geographic ranges, and that the rate of exotic gecko introductions to Caribbean islands may now be increasing.

Tracking the introduction of non-native reptiles is important for understanding the effects of non-native species and is potentially a process aided by citizen science. We present new observations of the mourning gecko, Lepidodactylus lugubris (Duméril and Bibron, 1836) on a new island in the Caribbean. Lepidodactylus lugubris was observed on Paradise Island, The Bahamas concomitant with citizen science observations on iNaturalist. An additional iNaturalist observation is presented, documenting a second report of L. lugubris on Grand Cayman, Cayman Islands. These reports demonstrate significant spreading of this non-native parthenogenetic species from its first record on a Caribbean island 10 years ago, the utility of citizen science observations for documenting the spread of non-native reptiles, as well as an observation of this species utilizing non-anthropogenic habitats in the Western Hemisphere, a potential precursor to detrimental effects on native species.

We report new observations of two invasive ascidian species, the solitary Ascidiella aspersa and the colonial Diplosoma listerianum, from Eastern Canada, which include some records from new sites. Because these species share many superficial characteristics with native and non-native species in the region, identification based on detailed taxonomic studies of internal structures—and not only on external features—are essential and can complement molecular methods. In this report, specimens of A. aspersa collected from Nova Scotia in 2013 and D. listerianum from New Brunswick and Quebec in 2017 were described morphologically to confirm species identity. Specimens of both were collected one year after initial discoveries in Nova Scotia and New Brunswick, respectively. Specimens of D. listerianum from Quebec were collected after a six-year hiatus. This report contributes a new record of A. aspersa 30 km (by sea) north of the site of the first record in Canada. It also confirms the first record of D. listerianum and documents its rapid spread in New Brunswick. This report is the first time that A. aspersa from Eastern Canada and D. listerianum from New Brunswick and the second time that D. listerianum from Quebec was explicitly identified based on an examination of internal features. Species confirmation of these easily overlooked or misidentified taxa contributes a time-stamp on current invasion fronts and suggests that the risk of further introductions and spread of these invasive species is present at un-invaded sites throughout Eastern Canada.

Vermetid gastropods are geologically useful as sea-level and palaeoclimatic indicators, and are known as bioengineering species that contribute to biological diversity. Vermetids are adapted to a sessile lifestyle but can sometimes be transported to distant regions and become non-indigenous and/or invasive species. Eualetes tulipa is considered invasive in Hawaii and Venezuela, and we detected it in 2009, inside Forno Harbour (22º58′22.39″S; 42º00′49.44″W) at Arraial do Cabo, Brazil in the southwestern Atlantic. Site surveys were performed at four depths to determine their occurrence, depth distribution, and size structures, including natural and artificial substrates. A total of 494 individuals of E. tulipa were recorded in the three sites investigated, with the highest population densities found on artificial substrates (breakwater) inside the harbour (1.5 ind m^-2) and at the greatest depth (4.0 ind m^-2). Their size structures indicated recent introduction, with the species spreading in the Arraial do Cabo region over natural and artificial substrates.

The spotted sea hare Aplysia dactylomela Rang, 1828 is reported from four locations in Libyan coastal waters. The direct observation reported here resulted from a field survey of sea snails in the coastal environs of Tripoli, to the west of the country, while the remaining records result from postings made on the Facebook™ social media website, made by recreational spear-fishermen who took images and filmed specimens at Abo Fatma beach and Misrata, to the west of the country, and also at sites close to Benghazi and Al Hamamah, to the east of the country. This is the first record of A. dactylomela in Libyan waters.

The non-indigenous amphipod Monocorophium uenoi was recorded for the first time on the French Atlantic coast. This species has been collected in Arcachon Bay and Bidasoa Estuary as early as 2007, probably introduced with non-native oysters. A summary on its morphological characters and its current distribution is done, and an updated identification key to Monocorophium species for European waters is provided.

Phtisica marina, originally described by Slabber, 1769 from Netherlands, is one of the most abundant caprellid amphipod species reported from numerous regions around the globe and is primarily associated with fouling communities in harbours. This study chronicles the further spreading out of P. marina into the Indian coastal waters. During a regular coastal survey in Gulf of Kachchh (Northwest coast of India), an established population of P. marina was observed in the subtidal regions of Vadinar and Sikka during April 2017. The caprellid could be a possible alien species in Indian waters as the species met the criteria for exotic taxa. The most possible introductory vectors and pathways are discussed in this study. As this species can survive in the stressed environments of low hydrodynamics and it has opportunistic behaviour, further studies are necessary to reveal its potential impact on local communities.

A flourishing population of the Massawan mantis shrimp, Erugosquilla massavensis, an Erythraean species, is recorded off Sicily, Italy, one year after the very first specimen was collected off the eastern coast of the island. The species is already established as a minor, albeit valuable, fishery resource. Once its population increases, however, it may compete with the native Mediterranean spot-tail mantis shrimp, Squilla mantis. This article presents the results of a joint effort between members of the Museo Civico di Storia Naturale of Comiso and local fishermen to monitor non-indigenous species in Sicilian waters.

We report new localities for Callinectes sapidus in the Iberian Peninsula that widen the north-eastern limit of its distribution by more than 206 km along the Iberian Mediterranean coastline. This invasive species has been captured in the estuaries of the Fluvià, Muga and Ter rivers and has become established in the Fluvià River in only nine months since the first individual was detected. These reports show how rapid expansion of C. sapidus can be and that this may be preceded by the presence of isolated individuals.

A single specimen of the invasive American blue crab Callinectes sapidus was captured at a depth between 0.5 and 1 m, by a fisherman in August 2018, near the estuary of the Oued Z’hor, in the eastern part of the Algerian coast. This report represents the first record of this species from Algerian coastal waters. Callinectes sapidus has widely invaded European Atlantic coasts and several areas of the Mediterranean, probably through ballast waters. However, information is still insufficient to ascertain the origin and mode of introduction of this species into the Algerian coast.

The Atlantic blue crab Callinectes sapidus Rathbun, 1896 is native in the western Atlantic, however it is a non-indigenous species across Europe since 1900, among other world regions. In this paper, we report the first occurrences of this species in the Ria Formosa lagoon and in the Guadiana estuary (SW-Iberian Peninsula, Europe) which occurred in 2016 and July 2017, respectively. We hypothesize that the introduction of this species into these ecosystems might be due to the expansion of the Guadalquivir estuary population through natural processes (larval advection, active movement), or due to unintended introduction events after being transported aboard fishing boats, or, less likely, through ballast water. Changes in Guadiana’s river flow after the construction of the Alqueva dam might also explain the presence of another non-indigenous species in the Guadiana estuary. The hypotheses presented, regarding the introduction of the Atlantic blue crab into these ecosystems and of its co-occurrence with other decapod species, are framed in a broader context to serve as a future research framework. The use of the Atlantic blue crab as a new fishing resource is also proposed, namely if it is to be used exclusively by local communities and if no deleterious impacts upon other fisheries and the ecosystem occur from this new fishery.

The capture of a male specimen of blue crab Callinectes sapidus (Rathbun, 1896) in the coastal waters of Matzaccara, Sardinia, Italy (South-Western Mediterranean Sea, 39°11′N; 8°43′E) is reported with morphometric data. The crab was collected by local small-scale fishery operators and brought to the attention of the Sardinian Forest Ranger Service/Environmental Surveillance and professional scientists. This record confirms the spread of this species in the south-western coastal habitats of Sardinia (Italy). The ongoing expansion of C. sapidus and its first appearance in the Sardinian fish market highlight the need for official sampling campaigns to update the population size of this non-indigenous species and evaluate its potential influence on the regional fishery sector. Control and mitigation of the ecological impact of C. sapidus can be coordinated with its possible exploitation as a future resource for the regional fishery sector.

Procambarus clarkii is among the “100 of the worst” invasive aliens in Europe. The geographic distribution and population dynamics of the species were studied for the first time in inland waters in the eastern Po Valley and its Delta, an area for which such information was absent. The geographic distribution of P. clarkii was assessed by sampling, in summer 2017, 12 geographically distant water bodies representative of an area of 3,000 km². Population dynamics was studied from 2017 to 2018, in a canal running through the town of Ferrara. Growth and longevity were estimated using the von Bertalanffy growth function. Procambarus clarkii was found in 100% of the water bodies sampled, indicating that red swamp crayfish has now completely colonized the eastern Po Valley, where interconnected field irrigation systems have allowed crayfish to spread almost everywhere. From the analysis of the polymodal frequency distributions, 5–6 growth cohorts were observed, each cohort corresponding to 1 year of age. Sex-ratio was 1:1, and no appreciable between-sex differences were found in growth patterns of crayfish population, except for the asymptotic length for which females approach higher values. Differences in life history parameters with other Italian populations may be due to latitudinal and different ecological conditions at our study sites.

Diver and remotely operated vehicle surveys have produced the first record of the invasive regal demoiselle, Neopomacentrus cyanomos, from the northern Gulf of Mexico (GOM) in July 2017. Several hundred individuals were observed associated with petroleum platforms and artificial reefs off the coast of Alabama. Initial taxonomic identification was made via morphometrics, coloration patterns, and meristic counts, and species was subsequently confirmed via DNA barcoding of the mitochondrial cytochrome c oxidase gene. This new finding represents a significant range expansion of the Indo-Pacific species in the greater GOM. Prior to our finding, there had been no reports of the species outside the southwestern regions of the GOM. Collection of early-stage juvenile specimens along with large adults suggests that further expansion is likely. Potential ecological impacts of a non-indigenous damselfish invasion are currently unknown and difficult to predict. Further study on the life history and ecology of the N. cyanomos population in the GOM, including their interaction with the invasive Indo-Pacific lionfish (Pterois volitans), will provide much needed information for understanding potential impacts and for management and mitigation of this species.

The Indo-West Pacific nakedband gaper, Champsodon nudivittis, was recorded for the first time in Saronikos Gulf (central Aegean Sea, Greece) on the basis of a single specimen collected by bottom trawl on 13 October 2017 at 89 m mean depth. DNA barcoding was used as a complementary tool to standard taxonomic features description for species identification. The present record corresponds to the westernmost expansion of this Lessepsian migrant, whose transition from the Levantine basin to the west was clearly associated with a deceleration in dispersal rate.

Knotweeds were introduced into Europe in the 19th century and soon after became aggressive invaders. While R. japonica and R. sachalinensis arrived from Asia, their hybrid Reynoutria × bohemica is believed to originate from the introduced range. Revised material shows that R. × bohemica has occurred in Europe since at least 1872, but was frequently misidentified as one of the parents. For that reason, the hybrid was detected relatively late in many European countries, meaning that it was silently spreading throughout the region for a long time. The present study was conducted in Croatia, where the parental species have been recorded since the 19th century, the hybrid, however, not being recognized until very recently, although it has probably been present for decades. As a result, the current knowledge of the distribution of knotweeds in Croatia is mostly erroneous. We revised specimens from Croatian herbaria and performed an extensive field survey across the whole of the territory of Croatia to collect new data. In this paper, we present accurate distribution maps of the three taxa, produced after a thorough revision, showing a result remarkably different to that previously known. In contrast to previously recorded distributions, we found that R. × bohemica is by far the most widespread, R. japonica is occasional, and R. sachalinensis is extremely rare. R. × bohemica, unlike its parents, occurs in Mediterranean Croatia as well. Compared to R. × bohemica, R. japonica occurs more frequently along watercourses. Taking into account that the studied taxa have different behaviour, ecological preferences, spreading ability and consequently different invasiveness, they should be analysed separately in any attempt to explain, manage and/or limit their spread. Therefore, the accuracy of their past and future identification is of major importance.

The Siam weed, Chromolaena odorata (L.) R. M. King & H. Rob. (Asteraceae), is recognized as one of the world’s worst tropical weeds. It is a perennial herb or shrub native to the neotropics that has become invasive across the tropical regions of Africa, Asia and Oceania. The species was introduced in 1937 in Nigeria and later spread to neighboring countries. Its presence and effects have been documented in the upland zones of almost all West African countries. Although, until the present study, the species had not been recorded in Guinea-Bissau, its presence in the country was very likely. In this work we document, for the first time, the invasion of Guinea-Bissau by C. odorata, assessing its present distribution and reporting effects, local uses and common names. Dispersal trends, potential consequences of its expansion and recommendations for management and control are also presented.