The increasing rate of marine invasions to Western Europe in recent decades highlights the importance of addressing the central questions of invasion biology: what allows an invader to be successful, and which species are likely to become invasive? Consensus is currently lacking regarding the key traits that determine invasiveness in marine species and the extent to which invasive and indigenous species differ in their trait compositions. This limits the ability to predict invasive potential. Here we propose a method based on trait profiles which can be used to predict non-indigenous species likely to cause the greatest impact and native species with a tendency for invasion. We compiled a database of 12 key biological and life history traits of 85 non-indigenous and 302 native marine invertebrate species from Western Europe. Using multivariate methods, we demonstrate that biological traits were able to discriminate between native and non-indigenous species with an accuracy of 78%. The main discriminant traits included body size, lifespan, fecundity, offspring protection, burrowing depth and, to a lesser extent, pelagic stage duration. Analysis revealed that the typical non-indigenous marine invertebrate is a mid-sized, long-lived, highly fecund suspension feeder which either broods its offspring or has a pelagic stage duration of 1–30 days, and is either attached-sessile or burrows to a depth of 5 cm. Biological traits were also able to predict native species classed as “potentially invasive” with an accuracy of 78%. Targeted surveillance and proactive management of invasive species requires accurate predictions of which species are likely to become invasive in the future. Our findings add to the growing evidence that non-indigenous species possess a greater affinity for certain traits. These traits are typically present in the profile of “potentially invasive” native species.

The spread of invasive non-native species, one of the greatest threats to biodiversity and the economy, affects the structure and functions of ecosystems at all levels. At the beginning of the 21st century a rapid expansion of the submerged macrophyte Elodea nuttallii was observed in southern and eastern Europe. However, this plant, native to North America, was already recorded in Europe in the first half of the 20th century. Our study aimed to evaluate changes in phytoplankton communities caused by the presence of this new invader. The research was conducted in a large floodplain lake in the Vistula valley (north-central Poland) and involved regular monitoring of the lake’s ecological status using phytoplankton-based methods. Long-term observations enabled us to track the impact of this invasive plant on phytoplankton and to compare the conditions of the phytoplankton community before and after Elodea nuttallii invasion. In the first stage of the research (2007–09) massive phytoplankton growth (max. biomass over 90 mg/L) and Cyanobacteria blooms (mainly of Aphanizomenon flos-aquae) were noted. Submerged vegetation along the shore was sparse and its development was inhibited by phytoplankton shading. Elodea nuttallii was first reported in this lake in 2009, together with native macrophyte species. The second stage of the research was carried out in the years 2013–15, when E. nuttallii had already colonised the lake, in some parts occupying the entire bottom surface and almost completely outcompeting native species of submerged macrophytes. As a consequence, the abundance and biomass of phytoplankton decreased. The highest biomass recorded in summer 2013–15 was approximately 4 mg/L. Secchi depth increased from 0.5 m in 2007–08 to 1.6 m in 2015. Elodea nuttallii expansion caused a shift from the turbid-water to clear-water state with higher water transparency. Phytoplankton blooms did not develop. The massive growth of E. nuttallii seems to have caused positive changes in the lake ecological status. However, E. nuttallii is considered to be a highly invasive species, threatening native hydrobionts at various levels of organisation.

Freshwater ecosystems are an easy target for invasive species given that aquatic plants possess specific traits that enhance rapid spread and colonization. The significant lack of knowledge on ecological demands and the current distribution of aquatic aliens is a crucial limitation to the effective protection and management of water bodies. In Slovakia, there are two established alien macrophytes that are widely distributed throughout the country: Elodea canadensis Michx. and Elodea nuttallii (Planch.) H. St. John. We focused on the temporal dynamics of colonization and the current distribution of both species, their ecological requirements and their effects on native flora and vegetation. We gathered 415 records of occurrence, including 168 for E. canadensis and 247 for E. nuttallii. Both Elodea species showed different temporal patterns of colonization of native aquatic habitats. Although the occurrence probability of E. nuttallii stabilized after an initial steep increase, the probability of E. canadensis occurrence showed a decreasing tendency over recent decades. The probability of species occurrence was significantly related to altitude and climatic characteristics. Mean January temperature emerged as the best predictor of the species distribution. Assessing the impact of both species, our results showed that elodeas contribute to the homogenization of natural aquatic communities. Specifically, species richness and beta diversity were lower in relevés with higher abundance of elodeas compared with uninvaded relevés.

The jellyfish Phyllorhiza punctata is native to Australia and has been widely regarded as a successful invader. In the Mexican Pacific, this species has been recorded in the Gulf of California, specifically in La Paz Bay and the coast of the Baja California peninsula, but the origin of its introduction to the Mexican Pacific is unknown. There is a poor baseline of knowledge and monitoring of this species; therefore, the present study provides genetic and morphological evidence of the reappearance of this exotic species in La Paz Bay, Mexico. The taxonomic identification of the specimen was carried out based on the morphological descriptions, and its identity was corroborated with the BLAST search tool and phylogenetic analyses. The collected specimen showed genetic and morphological evidence indicating that it belongs to P. punctata, whose distribution has expanded to tropical and subtropical coastal waters of 16 countries. Therefore, this study allows the establishment of a baseline for future studies of this invasive jellyfish.

The clam Rangia cuneata originating from the Gulf of Mexico has recently been introduced in the Baltic Sea waters. In the Polish coastal waters R. cuneata colonized riverine (the Vistula Delta) and the lagoon (the Vistula Lagoon) areas. In the Vistula Lagoon population strong fluctuations in clam biomass and density was observed being a consequence of reoccurring yearly spring mortality. In the present work we examined the condition and general health of R. cuneata from the Vistula Lagoon and the potential role of microorganisms as causative factors of mortality events. Overall, 102 adult clams were collected in March 2019. Out of those, 50 clams were used for microbiological and histological analyses while 52 for biochemical examination. Histological examination revealed that 47 clams were characterized by infiltration of hemocytes in various internal organs with mantle and gills most commonly affected. Observed inflammatory response was morphologically classified as mild to severe infiltrative hemocytosis as seen in severe systemic infections (septicemia) with the latter occurring in 40% of clams. Bacteria isolated from the clam tissues, characterized by a massive growth, included those from the genus Aeromonas (A. sobria, A. caviae, A. hydrophila), all classified as potential pathogens. Additionally, the presence of Kocuria spp. (G+) and pathogenic Shewanella putrefaciens (G−) was documented in one individual. Bacteria identified in water samples were almost identical to those from the tissue and included all the three Aeromonas species, S. putrefaciens and Staphylococcus pseudintermedius (G+). Gram staining revealed the presence of G(+) bodies in hepatopancreas, while G(−) bodies were often observed in the epithelial tissue of gills and mantle. Biochemical examination revealed the lack of glycogen, low carbohydrate and lipid contents indicating scarce levels of stored energetic materials. Hence, predominant bacteria isolated from R. cuneata together with low energetic reserves may greatly explain poor condition of these clams, and periodical mortality outbreaks occurring in the studied area. We thus hypothesize that the disease outbreak potentially elevating species mortality and affecting its reproduction may limit rangias’ success in creating a stable population in some areas with microorganisms forming mechanism participating in ecosystem resistance against introduced species during early colonization of the new environments.

The barnacle Austrominius modestus, native of New Zealand and Australia was introduced to the South of England around 1943 and has since spread to most coastal waters in Western Europe, including the southern North Sea. Apart from an ephemeral incursion into the Danish Wadden Sea in 1978, since 2010 it has established permanent populations capable of reproduction along the North Sea coast of the Jutland peninsula, the Limfjord, the north-western Kattegat, and the Skagerrak. It has probably invaded Danish waters by pelagic larvae originating in the German Wadden Sea. The species has since spread to other Danish localities, likely following the prevailing currents, but other means, as for instance transport by vessels, are possible. The barnacle inhabits stones, stone-reefs, mollusk shells, and live shore crabs in shallow waters. Based on hydrographical data from its native and recently invaded areas, we predict its future distribution to extend to most coasts of continental Europe except for brackish waters (< 20 PSU), and the Arctic seas. The northernmost distribution limit may include the Lofoten Islands of Norway.

Crayfishes are a diverse group of freshwater crustaceans which have proven to be harmful invasive species and are a leading cause of displacement of native crayfishes. Invasive species can harm populations of native species through hybridization which facilitates the displacement of native species and leads to a decrease in diversity. Hybridization has rarely been documented between crayfish species and the only genetically documented reports of North American crayfish species hybridizing have been between invasive rusty crayfish (Faxonius rusticus Girard, 1852) and two congeners. Virile crayfish (Faxonius virilis Hagen, 1870) is the most widely distributed crayfish in North America and occurs in its native range from the Hudson Bay watershed in Canada south to across the midwestern United States. Faxonius virilis has been introduced throughout North America and parts of Europe and is considered invasive in many locations. Faxonius virilis is invasive in the Ozark National Scenic Riverways (ONSR) in Missouri, U.S., and has been detected in the park since 1986. Setting out to document an updated range of F. virilis in the ONSR, we began developing a F. virilis-specific eDNA assay and noticed a discordance between the phenotype and mitochondrial DNA barcode of some native spothanded crayfish (Faxonius punctimanus Creaser, 1933) specimens. We compared mitochondrial, phenotypic, and microsatellite data and found that invasive F. virilis have hybridized with native F. punctimanus in the ONSR. Our research adds to the rarely documented occurrences of crayfish hybridization and supports previous researchers’ remarks that undocumented hybridization between native and non-native crayfish may be more common than previously thought. While the invasion of F. virilis has had a genetic impact on a native crayfish, the long-term evolutionary consequences are unknown.

The palaemonid shrimp Palaemon sinensis, a species native to China, was first discovered as an established non-native species in Japan in 2005, and it has since been reported in 25 of 47 prefectures. To genetically elucidate that P. sinensis was introduced to Japan from China via importation as a live fishing bait species, this study analyzed partial nucleotide sequences of the mitochondrial 16S rRNA gene of 165 specimens collected in 7 geographical regions in Japan (Tohoku, Kanto, Chubu, Kinki, Chugoku, Shikoku and Kyushu), and from 18 imported specimens from China purchased at a fishing store. All sequences were classified into 11 haplotypes, which included one widespread haplotype shared by more than half of the P. sinensis samples. Almost all of the samples of imported specimens possessed the dominant haplotype. Analysis of molecular variance showed no genetic differentiation between the Japanese local and imported samples or among regions in Japan. The overall results suggest that P. sinensis was introduced through human-mediated dispersal; furthermore, the haplotype distributions of P. sinensis established in Japan reflected the intensity of the species’ importation from central and northern China. This is the first study to document the genetic structure of non-native P. sinensis in Japan.

Dramatic declines of the native northeast Pacific mud shrimp, Upogebia pugettensis over the last three decades have occurred in response to intense infestations by the Asian bopyrid isopod parasite, Orthione griffenis, that was introduced in the 1980s. We report herein the arrival of the Asian mud shrimp, Upogebia major, in San Francisco Bay no later than 2006. Complications of identifying juvenile U. major and inefficiencies of collecting mature and readily identified specimens recovered by conventional sampling devices are likely to have delayed its identification and discovery. U. major is less vulnerable to O. griffenis and is displacing or replacing U. pugettensis in its present 200 km range to the north and south of San Francisco Bay. Upogebia major, as a coevolved alternative host, assures persistence of O. griffenis in this region even where native species extinctions occur and can potentially expand to all habitats that are presently invaded by O. griffenis (Alaska to Baja California Norte). The individual and combined O. griffenis and U. major invasions thus threaten U. pugettensis in particular and all other native Upogebia species occurring north of Mexico. Our review of Upogebia taxonomy for a key to species revealed a previously reported 1912 invasion of San Francisco Bay by Upogebia affinis that was in error; hence, the introduction of U. major is the first confirmed gebiid invasion in the world. Greater resolution of U. major natural history and timing of its invasion is needed to test whether it evaded present vector management efforts. Intervention is warranted to limit the doubled down U. major and O. griffenis invasion and to conserve U. pugettensis and other native Upogebia species from ecological or absolute extinction in the coming decades.

Pacific whiteleg shrimp Penaeus vannamei (Boone, 1931), a highly significant global commodity, has been introduced for aquaculture to many countries outside its native range, including Thailand. In Thailand, this species was introduced to replace Penaeus monodon for aquaculture in 1998, and it has represented more than 90 percent of total cultured shrimp production since 2005. The rapid expansion of P. vannamei aquaculture has led to escapes of P. vannamei into natural waters. We examined abundance, size and sex ratio of P. vannamei caught by commercial fishing gears, namely trammel, trawl and push nets, to determine the extent to which this species has entered the natural ecosystems in the Gulf of Thailand. Sampling was performed from August 2009 to October 2010 at five locations along the east coast of Thailand. We consistently found P. vannamei in shrimp catches in all three fishing gears across all locations. The frequency of occurrence of P. vannamei ranged from 0.13 (trawl nets) to 0.99 (push nets). The relative abundance by weight of wild-caught P. vannamei ranged from 0 to 5.43%, with highest mean abundance in Chanthaburi (0.42 ± 0.72%) and lowest mean abundance in Chonburi (0.04 ± 0.15%). All 4,041 individuals collected were sub-adults or adults (total length = 82 to 212 mm, weight = 3.2 to 71.8 g), with a 0.92:1 female to male ratio. The samples consisted of approximately 22% adults, suggesting a notable proportion of potential breeders in the wild. Our study can serve as a baseline for monitoring programs for aquaculture escapes. Our report is among the few studies that document substantial numbers of P. vannamei specimens throughout the study period. Participation by fishers proved valuable for detecting P. vannamei in the wild. Incorporating a similar sampling approach in fisheries monitoring programs will provide a consistent means of detecting population trends of P. vannamei in the wild.