Invasive aquatic plants can cause local losses of species diversity throughout the world and they can also contribute to water quality deterioration. Although widely studied elsewhere, little information exists about invasive aquatic plants and their impacts in China. This study summarizes the taxonomy, origin, vector of introduction, current distribution, and the ecological impacts of invasive aquatic plants in China. This study provides useful information for the management of freshwater habitats and suggests strategies for curtailing the increasing problem of invasive aquatic plants and their impacts. We integrated data based upon original research and a literature review to compile an inventory of invasive aquatic plants in China. In total, we found 152 invasive aquatic plant species belonging to 84 genera and 39 families, representing four major growth forms including emergent (57.24%), submerged (27.63%), rooted floating leaf (9.87%), and free floating (5.26%) categories of aquatic plants. The Poaceae (Gramineae) (23 species) was the most represented and species-rich family, followed by Alismataceae (14 species), Cyperaceae (13 species), Nymphaeaceae and Araceae (both with 10 species). The majority of the invasive aquatic plant species were introduced from South America, and there were also many from North America, Asia, Africa, and Oceania. Most of these species (96.05%) are obligate freshwater species, while a minority (3.95%) is limited to marine or intertidal habitats. The ornamental trade has been the most frequent historic pathway for the introduction of invasive aquatic plants.

Caulerpa taxifolia var. distichophylla (Sonder) Verlaque, Huisman and Procacini is a green alga of Australian origin recently reported as an alien species in the Mediterranean Sea, where it is known from SE Turkey, Sicily, Cyprus and Malta. In the current study we present additional records of this taxon, expanding its known distribution into the Eastern Mediterranean Sea, and provide additional records from Cyprus and the first records from Rhodes Island (Greece). Our specimens were identified through a combination of morphological and molecular methods involving sequencing of ITS and tufA. Locally, C. taxifolia var. distichophylla occurred in high abundances and dominated the benthic community, suggesting that has the potential to become a major pest in the Mediterranean. It was also observed over a very wide depth range, from the sea surface to at least 100 m depth, on a variety of natural soft and hard substrates as well as abandoned fishing nets, suggesting a broad environmental plasticity. One of the findings reported here constitutes the deepest record of an alien Caulerpa in the Mediterranean Sea, even though it remains to be demonstrated that it actually grows at this site and depth rather than being merely a drift specimen.

Hydromedusae, morphologically resembling the Indo-Pacific leptomedusa Lovenella assimilis (Browne, 1905) (Cnidaria: Hydrozoa: Lovenellidae), are reported for the first time in both the eastern English Channel and the southern bight of the North Sea. Analyses of past zooplankton samples from a long-term monitoring program suggest that this non-indigenous species has been present in the eastern English Channel at least since 2007. Genetic analyses identified specimens as Eucheilota menoni based on nearly identical 18S ribosomal RNA gene, mitochondrial cytochrome oxydase subunit gene I (COI) sequences, and 16S Ribosomal RNA gene. Consequently, published morphological descriptions of L. assimilis and E. menoni were compared, and their species status is discussed with regard to morphological and genetic evidence. In conclusion we suggest synonymizing these 2 indistinguishable species.

Environmental factors, such as temperature and salinity, are known to influence distribution patterns and invasion success in ascidians. The solitary ascidian Microcosmus exasperatus Heller, 1878 has a wide global distribution and can be found in both tropical and sub-tropical waters. In the Mediterranean Sea, it is considered to be an invasive species introduced through the Suez Canal, with a restricted distribution in the eastern Mediterranean. Despite its global distribution, the environmental tolerances of this species are poorly known. We examined the effect of varying temperature and salinity on the survival of adult individuals of M. exasperatus in a laboratory setting to partially determine its environmental tolerance range. In addition, it’s global and local distribution as well as the seasonal abundance in ‘Akko Bay (northern Mediterranean coast of Israel) were examined. Field observations and laboratory experiments show that M. exasperatus is able to tolerate a temperature range of 12–30 ºC, and salinity of 37–45, but it survived poorly in salinity of 33–35 and temperatures > 32 ºC. Considering this relatively wide tolerance range of M. exasperatus to temperature and salinity together with the anticipated rise in anthropogenic disturbances, we expect this species to further spread into new locations along the Mediterranean coast.

The North-American amphipod Gammarus tigrinus Sexton, 1939 is a successful invader in European waters due to its high reproductive potential and tolerance to severe environmental conditions and various pollutants. In this study, we followed the invasion and establishment of this exotic species in a species-poor ecosystem of the northern Baltic Sea. Two years after the establishment of G. tigrinus, over half of the sampling sites were occupied exclusively by G. tigrinus, whereas G. tigrinus coexisted with native gammarids in only one tenth of all sites. There was a clear separation of habitat occupancy between native species and G. tigrinus in terms of abiotic environment and macrophytic habitat. G. tigrinus preferred shallow sheltered areas dominated by vascular plants, while native species mainly occurred in more exposed, deeper habitats with phaeophytes and rhodophytes. In its suboptimal habitats, G. tigrinus exhibited moderate abundances, which allowed for the coexistence of native gammarids and the invasive gammarid. Since its establishment, the abundance of G. tigrinus has showed no signs of decline, with abundances exceeding almost fifteen times those of native gammarids at some locations. The results suggest that, irrespective to the competitive superiority of G. tigrinus over the native gammarids, the invasive G. tigrinus does not monopolize the entire coastal area of the northern Baltic Sea but mostly outcompetes native species in its favoured habitats..

The study of individual movement patterns and habitat choice is a fundamental step to assess an invasive species’ range extension and to inform possible management options. The spiny-cheek crayfish is an invasive species currently spreading in Europe and also in Lake Constance. This is of concern because the greater Lake Constance area still holds refugial populations of native crayfish that might be endangered by the invader. In invasive crayfish, individual movement patterns and the availability of suitable shelters can predict an invasive population’s spread. In a radio telemetry and mark-recapture study and in semi-natural outdoor experiments, we investigated movement patterns and shelter choice of spiny-cheek crayfish. In the field, radio-tagged and marked crayfish moved distances up to 1200 m within 4 and 13 days, respectively and mostly prevailed within the littoral zone at less than 3 m depth. Tracked crayfish resided close to artificial structures such as boat harbours in the study area. In the outdoor experiments spiny-cheek crayfish used litter as daytime shelter but also chose natural stones and macrophytes. We provide the first large-lake telemetry data on crayfish movement and our results suggest that spiny-cheek crayfish will expand its range within the lake moving along the shoreline. Artificial structures such as boat harbours and litter might facilitate this spread by providing suitable shelters. Our results can help to inform the implementation of countermeasures against the spread of invasive crayfish populations.

The Pacific white shrimp Litopenaeus vannamei (Boone, 1931) is native to the Pacific coast of Central and South America. This species was first introduced to Thailand in 1998 for aquaculture and as a replacement for Penaeus monodon Fabicius, 1798 because of problems with disease outbreaks and poor growth performance of the latter. Escapes of cultured L. vannamei to the wild were detected recently; however, little is known about the effects of the escape of cultured shrimps on the local ecosystems. In this laboratory study, the feeding behavior of L. vannamei was examined and compared with that of five native shrimps and a native crab species to determine the behavioral interactions and potential for food competition. With regards to palatability of the five native shrimp species, L. vannamei was non-selective, consuming the first piece of meat encountered. When all species were tested separately, Litopenaeus vannamei consumed its food faster than the native shrimps. In paired one-on-one contests, L. vannamei was much more aggressive in competing for food than the native shrimp species. When paired with the native crab species, Charybdis affinis, L. vannamei lost 100% of the contests and the crab sometimes killed and ate the shrimp. Due to its behavioural dominance in feeding contests with native shrimps, L. vannamei pose a serious threat to native shrimp species should it become fully established in marine waters of Thailand.

Although common carp are known to have been present in Ireland since the early 17th century, historically the species’ distribution was extremely localised. Owing to the popularity of carp as a sport fish in more recent times, it was suspected that the species range had expanded. Distribution maps were constructed from records in the published literature and consultations with both angling and governmental bodies, facilitating a review of the temporal changes in the range and distribution of carp from 1950 to the present day. There has been a significant increase in the range of distribution of carp, by order of 302% in the national 10 km grid-square network. The characteristic pattern of extinction and colonisation of carp in Irish water bodies clearly indicates that the species has not spread by natural dispersal but rather by human-mediated transfers, which are the mechanism for the species’ range expansion. While carp has been able to establish self-sustaining populations in Ireland, these remain restricted to smaller, often land-locked, water bodies. Future climatic warming and the increasing popularity of carp as an angling quarry may facilitate further range expansion, both naturally and human mediated.

The goby Padogobius bonelli is naturally endemic to northern Italy, but was introduced to several rivers in central Italy outside of its native range in the early 1980’s. In these watercourses, the rapid expansion of P. bonelli coincided with the decline of the endemic (for central Italy) P. nigricans. The two species share the same ecological niche and in laboratory studies it was observed that P. bonelli successfully and consistently outcompeted P. nigricans for breeding sites, preventing its reproduction. However, no studies about the effects of the introduction of P. bonelli on the biology of P. nigricans have been conducted in the field. The aim of this study was to investigate some life history traits of P. nigricans, including size at maturity, gonado-somatic index, fecundity and egg size and compare these datasets in terms of presence and absence of P. bonelli. Specimens were captured in the River Aggia, a tributary of the River Tiber. The introduced goby is present only in the downstream portion of the River Aggia due to the presence of a weir; thus, below the weir P. nigricans and P. bonelli live sympatrically, while upstream of the weir only the native goby is found. A total of 780 specimens of P. nigricans were collected, 547 upstream and 233 downstream of the weir. Females downstream of the weir produced a significantly higher number of eggs than females upstream, in both abundance and in relation to size. Several juveniles of P. nigricans (0+) were recorded upstream, yet downstream no juveniles were found in the months after the breeding period, with only a few small specimens captured during the winter season. These results highlight the difficulties that P. nigricans encounters in reproduction, possibly as a result of the competition with P. bonelli which poses a serious concern for the survival of the P. nigricans populations..

Fish community structure is a complex and integrated part of an aquatic ecosystem; a balanced system is often rich in species diversity and abundance. Invasive species can alter this balance, and the expansion of invasive silver carp may have similar deleterious effects. Recently, catches of silver carp in the Midwestern United States have increased and there is evidence of successful spawning and recruitment. However, early life history attributes of silver carp have not been fully evaluated within the Mississippi River Basin. A thorough understanding of early-life history is imperative to facilitate control efforts for silver carp populations. Furthermore, age-0 silver carp survival and subsequent recruitment may be regulated by habitat availability during this critical life stage. Thus, the objective of this study was to evaluate age-0 silver carp mesohabitat (i.e., depth, velocity, and substrate) use in three reaches of the Mississippi River Basin and potential habitat overlap with two native planktivorous fish species, gizzard shad Dorosoma cepedianum and emerald shiner Notropis atherinoides. Using data collected from the three lower most reaches of the Long Term Resource Monitoring Program (Pool 26 at Alton, Illinois, USA; Open River at Cape Girardeau, Missouri, USA of the Mississippi River; and the LaGrange reach at Havana, Illinois, USA of the Illinois River), we investigated age-0 silver carp, age-0 gizzard shad and age-0 emerald shiner habitat associations from 2007 to 2012. Overall, 79,358 age-0 silver carp, 89,990 gizzard shad and 41,119 emerald shiner were captured with mini fyke nets during this long-term study. Generally, all three species were collected most frequently in shallow (< 1.5 meters), low velocity (<0.6 meters/second) habitat with greater variability in substrate use ranging from silt to rock. Given the scarcity of these habitat types in the channelized Mississippi River Basin, our results suggest that invasive silver carp exhibit habitat overlap with gizzard shad and emerald shiner. This overlap may result in reduced growth and body condition of these fishes. To this end, this extensive data set has provided new information about silver carp early life history mesohabitat use and overlap occurring between two age-0 native planktivores in the Mississippi River Basin and potential consequences of this association

Propagule pressure is emerging as the most consistent predictor of establishment in non-indigenous species. Increasing propagule size (the number of individuals arriving in a novel environment at one time) is thought to increase probability of establishment by counteracting demographic stochasticity and Allee effects. Increasing propagule number (the number of introduction events) is thought to increase probability of establishment by counteracting environmental stochasticity. However, the relative importance of these effects and the conditions under which one effect may become predominant is largely unexplored. We first used stochastic population simulations, with a constant number of immigrants distributed over varying numbers of introduction events, to determine the relative importance of propagule size and number on the probability of establishment. Simulations were conducted under different environmental stochasticity and Allee effects regimes with parameters set to be representative of species with high risk of invasion. In absence of Allee effects, there was a slight increase in probability of establishment when going from very low to low propagule number. However, when Allee effects were included, probability of establishment consistently decreased with increasing propagule number. This pattern was consistent across a wide range of parameter values, and tended to be more pronounced when other model parameters resulted in low probability of establishment. This suggests that, within a range of conditions representative of non-indigenous species at high risk of invasion, large infrequent introductions are riskier than smaller more frequent ones. This is particularly true when Allee effects are likely to influence population dynamics at the early stages of the invasion process.