Introduced, or nonnative, marine species are a threat to local biodiversity, disrupt marine industries, and can have negative effects on coastal communities. Colpomenia peregrina (Sauvageau, 1927) is one of the most successful brown algal invaders in the world. Originating from the Northwest Pacific, Colpomenia peregrina was first collected in the Northwest Atlantic in Nova Scotia, Canada in the 1960s. Since then populations of C. peregrina have been discovered at 57 sites ranging from Grand Barachois Lagoon, Saint Pierre and Miquelon to South Wellfleet, MA, USA. The spread of Colpomenia peregrina can be attributed to its broad tolerance to environmental conditions, buoyant morphology that aids dispersal, and generalist epiphytic biology. Here we report the occurrence of Colpomenia peregrina at five sites in Rhode Island, USA for the first time, representing the crossing of a major biogeographic boundary by this species. The spread of C. peregrina will likely continue, warranting research on its impact on native communities and host algae.

The alien alga Caulerpa taxifolia var. distichophylla (Sonder) Verlaque, Huisman and Procaccini was first discovered in Malta in June 2013 and had spread to three sites spanning some 8 km by 2014. A monitoring programme in combination with a citizen science reporting initiative revealed a dramatic expansion in the distribution of this species, which was found at 23 sites over a 45 km stretch of coastline in 2016 and at four additional sites in 2017 (including three sites where it was previously absent in 2016). The alga is now distributed along the entire northeastern coasts of the Maltese Islands, as well as in northwestern and southeastern Malta, with mean frond densities of 91–972 fronds/m² and mean total frond lengths (including the rachis) of 12.3–41.8 mm. It was found at depths down to 40 m, predominantly on rocky substrata intermixed with other macroalgae (especially when the rocky substratum had a thick layer of sediment covering it) or on heterogeneous bottoms, including at the borders of Posidonia oceanica patches, but not within dense meadows of this seagrass. The remarkably rapid spread of C. taxifolia var. distichophylla and its ability to colonise several different habitats indicate that this alga should be regarded as invasive in Maltese waters.

Pistia stratiotes L. (water lettuce) is known as one of the most troublesome aquatic macrophytes, strongly affecting the environment and human activities in slow-moving and stagnant inland water systems. It was introduced into Europe in the 20th century and has since spread to 15 European countries. This paper presents data on the first record of this invasive aquatic plant in natural inland waters of Vojvodina (northern lowland part of Serbia) and discusses the possible pathways of its introduction. Field research was conducted in October and November 2017 on the Begej River in Vojvodina Province (Serbia), where populations of P. stratiotes were documented for the first time near Srpski Itebej, in close proximity (1.2 km downstream) of the Romanian border. The plant samples were collected, photographed in situ and deposited in the BUNS Herbarium. The relevant environmental data were also recorded in situ and water samples were collected for chemical analysis. This new record presents the first documented case of this invasive alien in rivers in Serbia, and expands upon the previous findings of this species in natural thermal waters of south-eastern and eastern Serbia. Taking into account the distance from the Romanian border and the fact that it has already been present in this country for several years, this introduction could be attributed to the spontaneous spreading of P. stratiotes from this neighbouring country. Nevertheless, despite this possibility, discarded aquarium plants cannot be entirely discounted as a potential source of this new introduction. Although it is hard to predict the exact consequences of this new introduction at such an early stage, bearing in mind the detrimental impacts P. stratiotes can have on the environment and excellent lateral connectivity of the Begej River with the canal and river network of Serbia, this finding highlights the need to take urgent action to control and instate regular monitoring measures, especially on the rivers and canals located close to the state borders.

Didemnum vexillum, an invasive colonial ascidian, has colonized natural and artificial substrates in Narragansett Bay, Rhode Island (USA) since 2000, when it was first discovered in Newport Harbor. A survey of the bay in 2005 found D. vexillum at several coastal sites in the southern portion of the bay, dominating substrata by the end of its reproductive period. The current study examines the near-surface geographic distribution of the ascidian in the bay in 2015 at less than 1 m depth, a decade after the initial survey. According to this study, the ascidian has a more limited distribution in 2015 than in the earlier 2005 survey. Artificial substratum presence, estimated mean salinity, and distance from Providence ports are all positively associated with the 2015 presence of the ascidian in the bay based on results from a linear discriminant function analysis. There are few investigations of long-term changes in invasive species distribution. Based on the findings of this study, further investigation of the causes of long-term change in the geographic distribution and abundance of invasive species, as well as the long-term impacts of such changes on native communities, are recommended.

The non-indigenous polychaete Ficopomatus enigmaticus, also known as the Australian tube worm, was recorded from Paul da Praia da Vitória (Praia da Vitória Marsh), Terceira island (Azores) in July 2016. This is the first record of this species on the Atlantic islands of the Macaronesia biogeographical region. At present, F. enigmaticus is exclusively in the lagoon of Paul da Praia where it is established and exhibits invasive behaviour. To explain the arrival of F. enigmaticus in this wetland system, which is not directly connected to the sea, we hypothesize natural mediated dispersal through migratory bird phoresy. This vector is crucial to consider in terms of risk assessments as this species spreads to other ecologically fragile areas. Potential impacts of F. enigmaticus on these sensitive and rare systems in the region are discussed.

The Mediterranean Sea faces unprecedented challenges by the increasing of non-indigenous species (NIS) introductions. Cyprus is the first European country affected by Lessepsian immigration, being along the natural pathway of many of the Indo-Pacific taxa spreading from the Red Sea; thus, it has a pioneer role in detecting alien species and in demonstrating that a concerted action is necessary at early stages of invasion, as required by the recent EU Regulation on NIS (EC/1143/2014). This study reports for the first time the presence of the nudibranch Goniobranchus obsoletus from Cyprus and confirms its spread in the basin, after its first sightings in Israel. Moreover, the records were collected in the context of a citizen project, this taxon being first detected by a scuba diver and then posted on a dedicated Facebook group. This study, therefore, proves once more the importance of technology utilization in early detection of non-indigenous species and suggests that citizen-science can form an integral tool for the implementation of the EU Regulation and should be further promoted by the national and international management authorities.

In this study, we focus on veronicellid slugs in the Ryukyu and Ogasawara Islands of Japan. We conducted phylogenetic analyses of these slugs, incorporating GenBank data from several veronicellid species. A molecular phylogeny based on the mitochondrial COI gene revealed that three clades inhabit these islands. We report here the first record of Semperula wallacei in Japan, which represents an introduced species in this region.

Here we report the first record of the red mouthed rock shell Stramonita haemastoma (Linnaeus, 1767) (Gastropoda, Muricidae) a predatory gastropod newly introduced to the English Channel. This species originally lives in the western Atlantic, eastern Pacific and Mediterranean Sea. Three specimens were collected on Pecten maximus at St-Martin-de-Bréhal, Normandy, France, on 2 February 2018. We present some hypotheses about the mode of introduction of S. haemastoma and its potential impact on the ecosystem in the English Channel.

This study presents the first occurrence and recent distribution pattern of the river nerite (Theodoxus fluviatilis L., 1758) in Lake Balaton. The first appearance of this Prosobranch snail was recorded along the western shore of the Tihany peninsula situated on the middle section of the lake, at 21st of October 2013 during a routine macrozoobenthos sampling. Occurrence of the species was also recorded along the eastern shoreline of the peninsula in 2015, and it became highly abundant in both areas in the following years. Results of a comprehensive survey conducted in the autumn of 2018 in the littoral region of the lake revealed that the river nerite has colonized almost the entire shoreline of Lake Balaton, only the westernmost and easternmost areas were still devoid of this invader, therefore it seems that its spread has not been finished yet. The river nerite appeared in extremely high abundances (up to 4–5000 individuals/m²) in the middle area of the lake, therefore it is likely that this species will have a significant effect on the biota of Lake Balaton, especially in the littoral zone of the lake.

The acute bladder snail Physella acuta (Draparnaud, 1805) was observed for the first time in the wild waters of Lithuania at one site in the lower reaches of the Nevėžis River in 2015. The restricted distribution and low density suggest recent introduction. Although P. acuta in the first half of the 20th century was reported in ponds of the Kaunas Botanical Garden, they appear to have vanished as of 2012. Thus we conclude that recent invasion into the wild most probably has resulted from disposal of aquarium organisms.

Invasive exotic species (IES) are one of the most important threats to aquatic ecosystems. To ensure the effective management of these species, a comprehensive and thorough knowledge on the current species distribution is necessary. One of those species is the New Zealand mudsnail (NZMS), Potamopyrgus antipodarum (J.E. Gray, 1853) (Tateidae, Mollusca), which is invasive in many parts of the world. The current knowledge on the NZMS distribution in the Iberian Peninsula is limited to presence/absence information per province, with poor information at the watershed scale. The present study aims to: 1) update the distribution of NZMS in the Iberian Peninsula, 2) describe its temporal changes, 3) identify the invaded habitats, and 4) assess the relation between its abundance and the biological quality of fluvial systems. We reviewed the available information and found 352 records covering all main river basins. NZMS can be found over a wide range of environmental conditions and habitat types. The relation between the biological quality and the abundance of NZMS suggests that an intermediate biological quality is the optimum for NZMS. Our study shows that NZMS is in a spreading phase in the Iberian Peninsula, which makes its control very difficult, especially because of its non-water mediated dispersion mechanisms.

Bradybaena similaris (Férussac, 1822) is an invasive land snail species native to East Asia, which is widely distributed in South America, including Argentina, Brazil, Colombia, Uruguay and Paraguay. In Argentina, very few previous records coming from the Tucumán and Misiones Provinces are available for the species. In this work, we report new occurrences of B. similaris in the country from Misiones Province, and include the southernmost record for the species in South America from Entre Ríos Province. We used shell morphology, morphological features of the reproductive system and radulae, and DNA sequences from 16S-rRNA gene for species-specific identification. These new distribution data reaffirm the need to monitor the southern dispersion of invasive snails in South America, especially those causing damage to several crop species.

The occurrence of the fragile cockle Fulvia fragilis (Forsskål in Niebuhr, 1775) in Libyan coastal waters (south-eastern Mediterranean Sea) is reported here for the first time based on the collection of twenty-nine live specimens from the shoreline in close vicinity to Tripoli Harbour, situated to the west of the country. The present record fills a gap in the geographic range of F. fragilis – its occurrence is already documented from the neighbouring territories of Egypt, Italy, Malta, and Tunisia. Although there are no certainties regarding the precise arrival date of this non-native bivalve in Libyan coastal waters, its presence within the environs of Tripoli Harbour might allude to its facilitated spread through ballast water from commercial shipping activity.

The occurrence of the Chinese pond mussel Sinanodonta woodiana is reported for the first time in the Molise region (Southeast Italy). Details of the mussel’s invasion history in Italy are also given. A total of 24 S. woodiana specimens were collected after a long drought period in October 2017 from an emerged beach on the southwest side of the Guardialfiera artificial lake and their main morphometric features were quantified. No young individuals were found, only large adults, whose survival could ensure population subsistence in more suitable environmental conditions. The present study provides evidence of a massive die-off affecting invasive bivalves during an extreme climatic event, producing decaying biomass with negative impacts on the water quality of the lake. Further investigations of the population dynamics of this species and the environmental quality of the water body are needed to develop an appropriate management plan in relation to the ecosystem services it delivers.

Aquatic invasive species (AIS) pose significant threats to the biodiversity of freshwater ecosystems worldwide. Consequently, it is crucial to understand the distribution and growth rates of AIS to protect susceptible lakes and rivers from potential invasions. Zebra mussels (Dreissena polymorpha) originated from the Ponto-Caspian region and were first recorded in the mid-1980s in the North American Laurentian Great Lakes. In 2013, zebra mussels were first observed in four harbours on Lake Winnipeg, Manitoba, Canada. Since then, the species appears to be spreading rapidly throughout Lake Winnipeg. Here, we present the results of the distribution of zebra mussels in the south basin of Lake Winnipeg along a 7 × 7 km grid. In fall of 2016, zebra mussels were widely distributed in the south basin of Lake Winnipeg. The highest observed density of zebra mussels on artificial substrate was 16.5 individuals per cm². Mean length of zebra mussels decreased with depth and latitude. This work provides valuable information for the management of AIS prevention and monitoring programs for waterbodies with similar conditions in Central and Western Canada and the United States.

The Central and South American mytilid mussel Mytella strigata was recently reported from the Philippines and Singapore, where its population has expanded exponentially in the last two years. We report the species has recently become widespread in the inner Gulf of Thailand, with densities reaching 40,800m^-2. It is a potential threat to lucrative Asian green mussel (Perna viridis) aquaculture and could be introduced to Australia, where it could foul pearl aquaculture farms. The concurrent finding of the invasive false mussel Mytilopsis sallei at two new sites in Thailand emphasises the urgent requirement for a detailed invasive marine species survey in the region.

Stephos cryptospinosus Zagami, Campolmi and Costanzo, 2000 and Stephos marsalensis Costanzo, Campolmi and Zagami, 2000 were found at Concarneau (Brittany, France). These species were originally described at the same locality on the island of Sicily (Italy) in the western Mediterranean. This report is the first record of either species from outside the Mediterranean Basin. The description of S. cryptospinosus is supplemented with SEM observations, and compared with the original. In addition, the role of the hyaline sheath covering the genital double-somite of the female in some species of Stephos is discussed.

Palaemon sinensis, a shrimp native to China, has now been recorded in numerous freshwater zones in Japan. The present study is the first report of the seasonal occurrence of P. sinensis in a river environment. Monthly field research was conducted from December 2015 to November 2016 at three sites in the lower reach of the Seno River, Hiroshima Prefecture, western Japan. At Stn. 1, in a side pool of the main river, P. sinensis was found throughout the year. Ovigerous females were present there from April to July, and undifferentiated juveniles from July to September. At Stn. 2, at a side bank of the main stream, the species was collected in December, January, and August to November; water velocity when P. sinensis was collected ranged from 3 to 8.5 cm/s. At Stn. 3, in a tide pool in the estuary zone, the shrimp was detected during months with relatively heavy precipitation (April and June) and in September–November; the range of salinity when P. sinensis was found was 0.1–22.7 ppt. No ovigerous females or undifferentiated juveniles were collected in the main stream or in the estuary zone. Together, these findings suggest a pattern wherein P. sinensis eggs hatch in riverside pools from April to July, with individuals then growing to a sexually differentiated size before dispersing and entering the main river stream, from approximately August to November, after which time they are probably only passively transported with the current into the estuary zone.

We report, for the first time in the wild, giant freshwater prawn Macrobrachium rosenbergii populations in East Africa. Specimens caught by fishermen in the lower reaches of the Ruvu River and Rufiji Delta in coastal Tanzania were identified based on their morphology, with confirmation through DNA barcode analysis. The East African specimens clustered with the western M. rosenbergii dacqueti subspecies in a phylogenetic analysis based on new and published mitochondrial 16S rRNA and cytochrome C oxidase subunit I (COI) sequences. Captured specimens spanned a size range of 110–310 mm total length and > 35% of females carried external eggs, implying that populations were established and self-sustaining. No active culture facilities or ponds with M. rosenbergii were found within the catchment. Nevertheless, the invasive populations supported a small-scale fishery that used bottom-set seine nets. The demonstrated presence of M. rosenbergii in at least two river systems, combined with the existence of favourable brackish water habitats for completing their life cycle, may indicate that river systems in East Africa are at a high risk of invasion by this species. Key information gaps for the region are highlighted.

Four hundred and forty seven specimens of a non-indigenous shrimp species were caught by local fishermen between the years 2016–2019, from Ma’deya shores, Abu Qir Bay, Alexandria, Egypt. These specimens were the Western Atlantic Xiphopenaeus kroyeri Heller, 1862, making this the first record for the introduction and establishment of a Western Atlantic shrimp species in Egyptian waters. Its route of introduction is hypothesized to be through ballast water from ship tanks. Due to the high population densities it achieves in this non-native location, it is now considered a component of the Egyptian shrimp commercial catch.

Invasive crustacean species have been present in the Long Island Sound, northwestern Atlantic Ocean, for over two centuries. Three new records of introduction are recorded here from collections by local fishermen. Two records are for male Dungeness crabs, Metacarcinus magister (Dana, 1852), collected in the Western Long Island Sound (2017) and Cape Cod Bay (2018). The other record is that of a range extension documented by a single male Chinese mitten crab, Eriocheir sinensis (Milne-Edwards, 1853), found in New Haven Harbor, Connecticut. Both species could potentially harbor nonnative epibionts and endoparasites. Additionally, E. sinensis may be more likely to establish, as it has in numerous locations in the region and worldwide.

The flat needlefish Ablennes hians was recorded for the first time from the Mediterranean. One specimen was captured on 23 September 2018, near the city of Netanya, Israel, ca. 20 km north of Tel-Aviv, and can be considered likely to be a Lessepsian migrant that entered the Mediterranean via the Suez Canal.

New data are reported on the Mediterranean parrotfish Sparisoma cretense in the coastal waters of Giglio Islands (North Tyrrhenian Sea). Using visual census strip transects, we documented the occurrence of both adult and sub-adult individuals, providing evidence on the existence of an established population of this species, 26 years after its first record in the same location. The potential of this warm adapted fish to further expand its distribution across the Mediterranean coasts is raised and discussed.

Asian weather loach species of the genus Paramisgurnus and Misgurnus can have a great invasive potential. In Europe, several feral populations of Asian weather loach have been reported, many of them within the distribution range of the native European weather loach Misgurnus fossilis, a declining species of high conservation concern. Distinguishing the different exotic species of weather loach can be difficult for the non-expert, as their general morphology is very similar, the coloration patterns are highly variable and the morphological characteristics may become degraded after preservation. We present the first molecular genetic confirmation of the presence of the large-scale loach Paramisgurnus dabryanus in Europe, after analyzing two specimens from a small pond along the brook “Wörthlinger Bach” (Danube catchment) in southern Germany. Accurate species identification is crucial both in the context of monitoring and conserving endangered species, and in detection and prevention of biological invasions. Therefore, we suggest the standard use of genetic species assignment based on mitochondrial DNA barcoding in monitoring cryptic fish species complexes, especially during potentially cryptic biological invasions.

The largemouth bass Micropterus salmoides (Lacépède, 1802), a North American fish from the family Centrarchidae, is reported for the first time from Bulgaria. In April–June 2018, adult largemouth bass (2+ years) were captured in two localities in the Struma River Basin (south-west Bulgaria). In May 2018, individuals from several schools of recently hatched M. salmoides were collected. The presence of multiple-age classes suggests that M. salmoides survives and reproduces naturally in Bulgarian freshwaters. The increasing number of reports of captured specimens along the Struma River suggests the species may be widespread. The largemouth bass was probably imported and dispersed in Bulgarian freshwater bodies by anglers without a prior risk assessment or authorization by the responsible institutions. In accordance with nature conservation efforts, to prevent further dispersal of the largemouth bass in Bulgaria effective management policies should urgently be developed and implemented by the appropriate authorities.

This paper provides the first report of the invasive Asian fish tapeworm, Schyzocotyle (Bothriocephalus) acheilognathi (Yamaguti, 1934), from Norway and Scandinavia. The parasite was found during routine post mortem disease examination of an imported koi carp, Cyprinus carpio, from an outdoor pond in the North of Norway. The intestine contained live tapeworms and these tapeworms were identified as S. acheilognathi by DNA sequencing of partial 18S and 28S ribosomal DNA and comparison of the obtained sequences with sequences in GenBank. The infected fish specimen along with the other fish in the pond were exterminated. The risk of infection from the pond to other fish outside of the pond was thus negligible. However, the finding of S. acheilognathi in imported aquarium fish shows that such import poses a risk of introducing pathogens to new areas. Had this fish pond been situated in the south of Norway where the temperatures are higher and where susceptible hosts are readily available, an escape of fish or release of eggs from the pond could potentially have resulted in infection of local fish populations.

The presence of Fibla maclachlani (Albarda, 1891) (Raphidioptera, Inocelliidae) has been recorded in Tuscany (central Italy) since 2005 according to information derived from both a biodiversity survey project and citizen science activities. The species, whose natural distribution includes the three main islands of central Mediterranean—Corsica, Sardinia, and Sicily—was most likely introduced into Tuscany through the raw cork trade from Sardinia. Further molecular comparative analyses are needed to confirm this hypothesis. This would be the first case of human-mediated jump dispersal in this family and a rare example of upstream colonization from island to continent. Two isolated records of F. maclachlani, an old (1905) and a very recent one (2018), are also reported from Calabria. The presence of F. maclachlani in Calabria remains unclear, the most reliable hypotheses are either the natural presence of the species at low population density or its introduction from Sicily at some point. The non-native populations of F. maclachlani currently coexist in the Italian peninsula in sympatry with the native inocelliid Parainocellia bicolor (A. Costa, 1855), a condition otherwise unknown among European species of this family. Future interactions between the two species are unpredictable.

Quadrastichus erythrinae Kim, 2004, which is considered a pest in Erythrina trees and is known in different tropical and warm regions of the world, is recorded in Panama, a country in the Central American region. Quadrastichus erythrinae were collected from galls on twigs and leaves of Erythrina variegata L. The presence of this species is expected to cause biodiversity and economic losses by affecting some ecosystem services such as habitat for species, nutrient recycling, primary production and soil formation.

Reports of amphibian invasions are increasing, although it seems likely that there are more extant populations of alien species than we are currently aware of, and we are far from understanding their full environmental and economic impact. Here we provide data on another established population of African clawed frogs, Xenopus laevis (Daudin, 1802); from Yunnan Province in mainland China. The site is an aquaculture area immediately adjacent to the northern shores of Lake Kunming. This report is significant as it is the first known alien population of an albino form of this species, the form that is most prevalent in the pet trade. We call for urgent surveys using eDNA to determine the extent of the invasion of this cryptic amphibian invader around Lake Kunming, as well as studies to determine the environmental and economic impacts at this site, which is already known for an invasion of American bullfrogs, Lithobates catesbeianus (Shaw, 1802).

Golden tegus (Tupinambis teguixin sensu lato) are native to South America but have established a reproducing population in Miami-Dade County, Florida. Recent work divided the golden tegu into four distinct species, leaving the specific identity of golden tegus in Florida unknown. We used morphometric and mitochondrial data to determine the species identity and likely area of geographic origin for a specimen of golden tegu collected in Miami-Dade County. Our results confirm that cryptic golden tegus (Tupinambis cryptus) are at least one of the species established in Florida. Their geographic origin is likely mainland Guyana or Venezuela. The presence of T. teguixin in Florida remains possible, based on other specimens of ambiguous scalation. Further study is needed to determine the identity and origin of these populations.