The cryptic invasion of North American aquatic ecosystems by non-native haplotypes of Phragmites australis (Cav.) Trin. ex Steud., 1841, has been well documented. Most research has focused on eastern Canada, and the eastern seaboard, St. Lawrence waterway, southwest (Utah), and Gulf coast regions of the United States. Less has been published on the extent of this invasion in the north central United States. In this report, 69 populations of Phragmites australis were identified and sampled within the Minnesota and Mississippi River corridors of Minnesota, as well as from roadway drainage ditches within the greater Minneapolis-St. Paul metropolitan region (MSP). Restriction fragment length polymorphism analysis and DNA sequencing were used to determine the cpDNA lineage of each population. All populations sampled within the river valleys were native North American haplotype E, as were most MSP populations. However, numerous isolated populations of Eurasian haplotype M Phragmites australis were identified along MSP transportation corridors. Nuclear microsatellites indicated that these M haplotype populations are not clonal. These results show that Eurasian haplotype M Phragmites australis has become established in at least one region of Minnesota, but has not yet widely invaded the riparian wetlands of Minnesota’s two largest rivers. This provides a baseline for continued monitoring of the spread of this invasive plant.

he freshwater hydrozoan Craspedacusta sowerbii was observed for the first time in Ireland at five localities in two separate river catchments (Shannon and Erne) during the summer of 2013. All collected medusae from Lough Derg on the Shannon catchment were female. Analysis of water temperature data for the period 2001–2015 found that water temperatures greater than 21°C were only recorded in 2013. The occurrence of medusae in three distinct areas during this unusually warm summer suggests that it may have been present in its polyp form for some years, or even decades. While it is not known when the species arrived in Ireland, the spread of this species may have involved different pathways. With climate warming, further appearances of the medusa-stage may be expected.

Anthropogenic removal of natural dispersal barriers and modification of natural habitats have contributed to the spread of non-native species. Potential invaders that are cryptic in appearance and/or behaviour are particularly troublesome as this confounds efforts to detect or manage incipient invasions. Here we report one such invader, the Florida serrate crownsnail, Pyrgophorus platyrachis Thompson, 1968, in Singapore reservoirs—only the first record outside the Americas. We identified P. platyrachis using morphological and molecular techniques. The Singapore COI mitochondrial sequences were 99–100% matched to P. platyrachis from Florida, USA, while the 16S sequences are the first published for this species, and were most closely matched to another confamilial species.

The dark false mussel, Mytilopsis leucophaeata, has been found in very specific habitat in the Archipelago Sea (northern Baltic Sea) and now has spread. Between 2011 and 2015, we collected small numbers of M. leucophaeata at three sites 10 to 28 km apart in soft sediment habitats with pier structures and rocks in water 2–3 m deep. Previously, M. leucophaeata in the northern Baltic Sea was restricted to areas receiving cooling water discharge from nuclear power plants. Our findings were from areas without a source of heated water, and the closest known occurrence of M. leucophaeata is 120 km away. It is evident that this species is expanding its distribution in the Baltic Sea area and is not restricted to areas having anthropogenically-warmed water.

The non-native amphipod Melita nitida Smith, 1873 was collected between 2013 and 2016 in Arcachon Bay, Hossegor Lake and the Gironde Estuary (SW France) in intertidal oyster reefs and under stones. This species, native to the Atlantic coast of North America, is considered as a non-indigenous species on the Pacific coast of North America. Recently, the presence of M. nitida was reported in Europe, both in The Netherlands and in Germany. This species may have been accidentally introduced to Arcachon Bay with oyster transfers. An identification key for species belonging to the genus Melita and closely related species in European waters is also provided.

The freshwater palaemonid shrimp, Palaemon sinensis was imported into Japan from China as live fishing bait, and its introduction has become a concern in Japanese freshwater areas. In the present study, field research was conducted to confirm the distribution of this invasive shrimp in eight rivers in Hiroshima Prefecture, western Japan. We found caridean shrimp, such as P. sinensis, Palaemon paucidens, Palaemon serrifer, Palaemon macrodactylus, Palaemon orientis, Macrobrachium nipponense, Caridina leucosticta, and Neocaridina spp.. P. sinensis was found in four rivers. A longitudinal distribution analysis showed that P. sinensis occurred in the lower reaches, whereas P. paucidens showed a wider distribution from the upper to the lower reaches. Palaemon sinensis occurred in a narrow range of stream velocity (0–2 cm/s) compared with that of P. paucidens (0–18 cm/s). P. sinensis density was negatively correlated with river velocity, indicating that this shrimp prefers a lentic water environment.

Since at least 2009, the Harris mud crab Rhithropanopeus harrisii (Gould, 1841) has been spreading in the northern Baltic Sea, an area with no native crab species. Thus far, this species has invaded muddy and rocky coastal areas, especially shallow habitats dominated by reeds and the brown macroalga Fucus vesiculosus Linnaeus, 1753. Here, we document the first sighting and recruitment of mud crabs in an eelgrass Zostera marina Linnaeus, 1753 meadow - a critically important habitat for fish and invertebrate species. We found both adult and juvenile mud crabs in repeated sampling over the summer, suggesting continuous use of eelgrass as habitat for mud crabs and recruitment into the meadow. Given the simple food web structure of the Baltic Sea, this novel predator could lead to new energy pathways with unexpected consequences and potentially important effects on the functioning of the native eelgrass community.

Gambusia affinis (Baird and Girard, 1853), a notorious non-native invasive fish species, has negatively impacted aquatic ecosystems around the world. This species was recently identified in Lake Kenyir, one of the largest impoundments in South East Asia, using DNA barcoding. The coxI sequence of Gambusia caught in Lake Kenyir was compared with the sequences of topotypic voucher specimens of G. affinis and two other candidate Poeciliidae. The species was found to cluster with G. affinis but not with monophyletic clades of either G. holbrooki or P. reticulata thus confirming species identity. The fish is yet to be widely established in the lake with the current distribution limited to areas of anthropogenic disturbance.

Non-native red lionfish Pterois volitans (Linnaeus, 1758) and devil firefish Pterois miles (Bennett, 1828) have become established on continental shelf areas throughout the western Atlantic Ocean, the Caribbean Sea, and the Gulf of Mexico. Lionfish were first observed in the Gulf of Mexico in 2009, and sighted at Flower Garden Banks National Marine Sanctuary (FGBNMS) in 2011. We document the first appearance of lionfish and sighting frequency in FGBNMS using fish surveys from long-term monitoring data, diver sighting and removal data, and observations from Remotely Operated Vehicle surveys. Our results quantify and identify trends in lionfish density, biomass, and sighting frequency within the national marine sanctuary. Lionfish populations demonstrated different patterns among the three banks of FGBNMS. While lionfish have shown a steadily increasing trend at East Flower Garden Bank and West Flower Garden Bank from 2011 to 2014, populations decreased at Stetson Bank following the initial invasion. Because lionfish populations are projected to increase throughout the Gulf of Mexico, the continuation of long-term monitoring and volunteer diver programs with the combined analyses from multiple data sets similar to those used in this study are vital in early warning, detection, and documentation of invasive species and time-sensitive management issues.

The squirrelfish genus, Sargocentron, is reported for the first time from Maltese coastal waters within the Central Mediterranean. The record is based on two individuals caught at two different coastal locations in the Maltese Islands within the space of a few days of each other, through the same fishing technique (trammel nets). In view of the impossibility to collect meristic, morphometric and molecular data from the recorded individuals, and due to the close similarity between a number of Sargocentron congeners, the exact taxonomic identity of the captured individuals could not be conclusively confirmed, although the livery on the two caught individuals resulted to be consistent with that of S. rubrum and S. hastatum.