We report the return of the alien seagrass Halophila stipulacea (Forsskål) Ascherson, 1867 (Hydrocharitaceae) in the harbor of Palinuro (Salerno, Tyrrhenian Sea, Italy), six years after the local extinction of this species in this area in 2011. The record of this new colonization event of H. stipulacea in Palinuro represents the northernmost location of this tropical alien seagrass in the Western Mediterranean. The species, when first studied in June 2007, had a bottom cover of 16 m², which was reduced to 4 m² in 2009, and to 2 m² in 2010. In 2011, the species was no longer detectable and was considered extinct in the area. In September 2017, the species was recorded again in the area in a few zones, close to where it was originally observed, and covering approx. 5.5 m². Seven patches were monitored, occurring between 1.5 and 4 m depth, and with a mean shoot density of 6,300 shoots/m², mean leaf length of 33.8 mm, and mean width of 5.3 m, while flowers were absent. Evidence of strong grazing (bite-marks) was observed on 57% of the H. stipulacea leaves by native fish species.

Coastal estuaries represent areas of high biological invasions by virtue of their economic importance as ports. We report on the first occurrence of the non-native hydrozoan Moerisia sp. in coastal New Jersey, USA. Through the use of artificial settling plates, several diminutive, unknown cnidarian polyps were isolated. Initial morphological assessment indicated that two of the unknown polyps were keyed to Moerisia. We then used universal cnidarian primers to amplify and sequence the 16S rDNA mitochondrial locus for molecular identification. Upon evaluation and editing of sequences, two of the unknown polyps were identified as belonging to a group of unresolved Moerisia sp. taxa (> 99% homology). Additionally, polyps of Chrysaora and Aequorea were also identified from settling plates. The presence of Moerisia sp. in Barnegat Bay is the second recent documentation of an invasive hydrozoan in New Jersey and suggests that there may be other undescribed hydrozoans in this region that have yet to be been recognized, especially those with cryptic benthic life history phases.

Among Sabellidae (polychaetes commonly found in hard substrate fouling communities), the genus Branchiomma Kölliker is a species-rich group with an expanding global history of invasions. In this paper, we report the first new records of Branchiomma bairdi along the Californian and Hawaiian coasts. Moreover, we confirm the first recorded introduction and range extension of Branchiomma conspersum. Branchiomma conspersum is originally from the Caribbean Sea and is a new non–indigenous species on the Pacific side of Panama and is also present in Hawaii and Australia.

We report two new, curious records of freshwater worms collected in the Panama Canal, Panama: the ribbon worm, Apatronemertes albimaculosa Wilfert and Gibson, 1974, and the leech, Placobdella parasitica (Say, 1824). Identification of these specimens relied on morphological examinations and, more heavily, on molecular barcoding using the mitochondrial COI locus. Both phylogenetic and genetic distance analyses were employed to robustly establish the identities of the specimens. Whereas the native range of A. albimaculosa is currently unknown, P. parasitica was first described from Minnesota, USA and is possibly native to southern Canada and most of the USA. Neither species has previously been recorded from Central America. We briefly discuss possible scenarios for the dispersal of both species, and conclude that the introduction of P. parasitica into Panamanian waters was likely human-mediated in association with the introduction of its turtle host. Insofar as ours is the first record of wild-caught A. albimaculosa worldwide, we do not exclude the possibility of Panama being within the native range of the species. However, it is also possible that the species has been transported with ballast water into the Panama Canal; a relatively common phenomenon.

We report new findings of non-indigenous Indo-Pacific molluscs from shallow water habitats off Israel, Greece and Egypt, eastern Mediterranean Sea. The bivalves Pillucina vietnamica Zorina, 1978 and Alveinus miliaceus (Issel, 1869) were collected from sandy bottoms off Israel, whereas Gregariella cf. ehrenbergi (Issel, 1869) was recovered from a buoy originating from Port Said, Egypt, and stranded on the Israeli coast. The three species are first records for the Mediterranean Sea. Additionally, we report range extensions for several gastropods: Varicopeza pauxilla (A. Adams, 1855) is recorded from Israel, Phidiana militaris (Alder and Hancock, 1864) from southern Israel (Ashqelon), and Viriola cf. bayani Jousseaume, 1884 from Israel and Crete. Shells and valves of an unidentified lucinid bivalve morphologically distinct from any known Mediterranean species were found along the Israeli Mediterranean shore.

The Asian clam Corbicula fluminea has spread rapidly through western Europe and was first recorded in Ireland in 2010. Since then it has been found within four different river catchments including four localities along Ireland’s largest river, the Shannon. While three of these Shannon occurrences may have been due to introductions with angling equipment or leisure craft, subsequent expansions will have resulted from natural spread. The dispersal of this clam within two temperate lakes of > 100 km² was examined over a six year period to the autumn of 2016. Downriver and down lake water flow and currents generated by wind result in young clams being distributed by means of a byssal dragline that would appear to explain the distributions obtained.

Although an invasion of the brackish water biotopes was to be expected with the appearance of several Ponto-Caspian amphipods in German freshwaters two decades ago (and earlier), only recently (two years ago) the conquest of the mesohaline Baltic Sea could be observed. This discrepancy is a fortiori of interest as previous experimental studies showed that species like Dikerogammarus villosus and Obesogammarus crassus were able to tolerate both mesohaline and also polyhaline conditions. Two decades of invasion history in rivers and lakes have led to drastic faunal changes. If similar or analogue shifts will happen in brackish environments and if estuaries like the Stettin lagoon function not only as “a gate to the Baltic Sea” but also as a “catalyser” or acclimatisation area for invasive species remains to be seen. Simultaneously the question came up, why other also potentially brackish water species failed to colonise mesohaline waters although they partially arrived in the investigation area several decades ago (e.g. Chelicorophium curvispinum and Echinogammarus ischnus).

The caprellid Paracaprella pusilla from the Western Atlantic Ocean is reported for the first time in Golfo de Nicoya, Pacific coast of Costa Rica, representing the third registered invasion of this species in the Eastern Tropical Pacific (ETP), after Panama and Mexico. Individuals of P. pusilla at all stages of development, including juveniles, females (non ovigerous and ovigerous) and males, were sampled from submerged artificial structures at five locations along the coastal waters of Golfo de Nicoya between September 2014 and September 2017. This new report for the ETP indicates that the amphipod is well established in a tropical estuary of Costa Rica: Golfo de Nicoya, and represents the first caprellid reported from littoral waters of this country.

The Ponto-Caspian amphipod Dikerogammarus bispinosus is regarded as a native species throughout the lower stretches of rivers that drain into the Black Sea. Its occurrence in the Caspian Sea basin was uncertain due to conflicting reports. Here, we provide the first conclusive evidence for its presence in this basin. Individuals of both sexes, including ovigerous females, were collected in May 2000 from the Ural River in Kazakhstan, suggesting full establishment. If it was a recent invasion, the most probable dispersal pathway into the Caspian basin would have been via the Volga-Don canal as D. bispinosus was reported in the early 2000s from the lower Don River and the Saratov reservoir on the Volga River. However, given that until relatively recently D. bispinosus was considered a subspecies of D. villosus, we cannot rule out that it has been overlooked in earlier reports from the Caspian Sea basin by being mentioned as D. villosus or even D. haemobaphes. We also provide new data on the distribution of Gammarus lacustris, Obesogammarus platycheir, Pontogammarus abbreviatus, P. robustoides, Turcogammarus aralensis and Wolgagammarus dzjubani in western Kazakhstan and southwestern Russia.

Seven specimens of the northern brown shrimp Penaeus aztecus, a western Atlantic species, were collected in December 2016 and in November 2017 by bottom trawlers off Termoli, on the central Adriatic coast of Italy. The various colonization scenarios put forward as explanations for the species’ sudden, near concurrent presence in distance sites within the Mediterranean Sea and nowhere else, are discussed. The species is already established as a valuable fishery resource in southeastern Sicily, and is likely to do well in the Adriatic Sea, once its population increases.

The Asian tiger prawn (Penaeus monodon) is considered an established non-native species throughout the greater Caribbean, Gulf of Mexico, and southeastern United States. A previous investigation on the non-native distribution of P. monodon documented its presence in south Florida. Here we update information regarding its south Florida presence and report our capture of a specimen that may be the smallest tiger shrimp juvenile yet observed in the Western Atlantic Ocean. Continued reports of both adult and juvenile P. monodon from Nov. 2011 through Aug. 2017 suggest that the species is established in the south Florida region. One of several goals of the Comprehensive Everglades Restoration Plan is to reduce the salinity of nearshore waters to approximate conditions prior to construction of levees, canals, and control structures. An unforeseen consequence of this massive restoration program could be the facilitation of P. monodon population retention and further expansion in south Florida. P. monodon would likely be able to outcompete native species under lower salinity conditions; continued vigilance and laboratory experimentation could improve knowledge of P. monodon’s potential advantages.

Invasive parasites represent a serious problem due to their capacity to threaten local populations of native (often endemic) hosts, and fishes in breeding facilities. Tapeworms (Cestoda) are extremely adapted (they lack any gut and circulatory system) parasitic flatworms some of which have colonised new geographical regions as a result of unintentional transfer of hosts infected with these parasites. The highest number of invasive parasites within this host-parasite system is among tapeworms parasitizing common carp (Cyprinus carpio L.), which has also been introduced globally. In the present study, we report another record of the Asian non-native fish tapeworm Khawia japonensis (Yamaguti, 1934) (Cestoda: Caryophyllidea) from common carp in Europe. Previous records of this cestode from Italy (Po River basin) and Slovakia (Danube River basin) and its present finding in the Czech Republic (Elbe River basin) confirms recent expansion of the parasite in Europe. Potential impacts of this non-native parasite on common carp in commercial breeding fisheries should be carefully studied.

The western mosquitofish (Gambusia affinis Baird and Girard, 1853), which is considered one of the 100 worst invasive species in the world, has been introduced to China. However, there is little information on the biological characteristics of mosquitofish in China. To better determine how this invasive species might impact China, the life-history traits of western mosquitofish were studied in the central Yangtze River from April 2012 to March 2013. A total of 962 mosquitofish specimens were collected. The size of females and males ranged from 12 to 44 mm and 12 to 29 mm, respectively, and the maximum ages of males and females were 0+ years and 1+ years, respectively. Both sexes grew allometrically (males: negative (b = 2.593); females positive (b = 3.253)). Females were numerically dominant with an overall female-to-male sex ratio of 1.65:1. Specifically, the female-to-male sex ratio was higher in summer (2:1) and autumn (3:1) and did not deviate from the theoretical value of 1:1 in winter and spring. The smallest pregnant female had a total length of 21 mm, and fecundity ranged from 4 to 65 eggs. Compared with the findings obtained in other studies, the western mosquitofish population in the central Yangtze River is characterized by faster growth, lower fecundity and shorter life span. These traits might enable the successful invasion of mosquitofish in the central Yangtze River.

Eight individuals of the brown bullhead, Ameiurus nebulosus (Lesueur, 1819), were caught in an artificial pond in the city of Lviv, Ukraine, in September 2017. This is the first report of this alien invasive species in the Dniester River basin. It indicates its expansion in Ukraine and also, generally, in Europe.

The first report of the invasion of the Robber frog Eleutherodactylus johnstonei Barbour, 1914 in the municipality of São Paulo was made in 2014. However, we report here that sound records of this species in the same area of São Paulo, and deposited in a Brazilian sound archive, date back to 1995. Therefore, we expand the timeframe of the presence of this invasive population in the city, and provide information on its pathway of introduction, which is not accidental as previously suggested, but intentional. These data improve the knowledge on this invasion and indicate the urgent actions to avoid the expansion of this invasive species to other sites where its impact could be higher.

The silverfish Ctenolepisma longicaudata (Escherich) (Zygentoma, Lepismatidae) is an invasive, synanthropic, warehouse, and economic pest, probably of Central American origin. During recent decades, its occasional occurrence has been recorded from some European countries. Here, we report the first established population of C. longicaudata within the territory of the Czech Republic. In the autumn 2017, the population was discovered in a warehouse and surrounding office buildings in Prague. Since this species causes damage to starch components and fabrics as well as food contamination, we strongly recommend further monitoring and possibly eradication.

Citizen scientists make important contributions to the collection of occurrence data of non-native species. We present two datasets comprising more than 520,000 records of 1,771 non-native species from Flanders and the Brussels Capital Region in Belgium, Western Europe, collected through the website http://www.waarnemingen.be hosted by Stichting Natuurinformatie and managed by the nature conservation NGO Natuurpunt. Most records were collected by citizen scientists, mainly since 2008. Waarnemingen.be aims at recording all species, native and non-native, and it is shown here that this kind of biodiversity portals are also particularly well suited to collect large amounts of data on non-native species. Both datasets presented here are also discoverable through the Global Biodiversity Information Facility (GBIF).