Several taxa forming a species complex within the bryozoan genus Watersipora are successful global marine invaders that are common in marine fouling communities in bays and harbors. This species complex has recently been recorded spreading to natural intertidal and subtidal habitats on the central California outer coast near the San Francisco Bay, suggesting that its invasive potential is greater than previously believed. To determine the species and clades present in these outer coast populations, and their relationship to populations in nearby bays and harbors, we produced COI sequences for a set of new Watersipora specimens sampled from four rocky intertidal sites, for which there is currently no published genetic data. Watersipora subtorquata and Watersipora new species were both identified at rocky intertidal sites. All haplotypes identified in this analysis have previously been reported in California harbors and marinas, suggesting that intertidal populations may be sourced from existing populations in harbors, rather than representing independent invasions. Field observations of intertidal populations support Watersipora’s year-round persistence at rocky intertidal sites, which has significant implications for invasion dynamics and invasion management strategies. Continued sequencing of outer coast Watersipora samples will be crucial to further characterize the genetic diversity and structure of these coastal populations and describe the dynamics of Watersipora’s outer coast spread.

The dreissenids, quagga mussel Dreissena bugensis and zebra mussel D. polymorpha, are invasive freshwater mussels in Europe and North America. These species strongly impact aquatic ecosystems, such as the food web through their high abundance and filtration rate. They spread quickly within and between waterbodies, and have the ability to colonize various substrates and depths. The zebra mussel invaded and established in Swiss lakes in the 1960s, whereas the quagga mussel was not detected until 2014. We collected all available data from cantonal as well as local authorities and other institutions to describe the colonization pattern of quagga mussels in perialpine lakes north of the Alps. We also collected data regarding the distribution of larval stages of the mussels, the so-called veliger larvae. We observed that in lakes colonized by the quagga mussel, veligers are present the whole year round, whereas they are absent in winter in lakes with only zebra mussels. Additionally, we present detailed information about the invasion and colonization pattern of quagga mussels in Lake Constance. Quagga mussels colonized the lakeshore within a few years (~ 2016–2018), outcompeted zebra mussels, and have reached densities > 5000 ind. m^-2 in the littoral zone, even at 80 m densities above 1000 ind. m^-2 were found at some locations. At the end of the article, we discussed possibilities on how the spread of quagga mussels within and among northern perialpine lakes should be monitored and prevented in the future.

The newly established population of Perna perna surveyed at four sites along the Israeli Mediterranean coast averaged between 2155 and 8022 specimens/m² in June 2021. Three sites displayed unimodal size–frequency distributions, whereas the site adjacent to Haifa port – a bimodal distribution. The population suffered catastrophic mortality following a succession of heatwaves culminating in a prolonged heatwave in August (ambient temperature 36 to 38 °C, sea surface 32 °C), with diurnal low tides occurring midday. With the projected rise in both mean temperature, and prevalence, duration, and severity of extreme high temperature events, it is likely that even if a P. perna reoccurs, it will be of brief duration.

Recent invasions of the North and Baltic Seas by three Marenzelleria species have extensively altered benthic communities in the region. Despite several studies on the morphology and biology of the worms, their morphological identifications are often challenging. Here we summarize and map the available records of Marenzelleria from Eurasia, distinguishing those based on morphology versus molecular data. Based upon the genetic similarity (p = 0.08% for COI) between individuals from the Baltic Sea and individuals from the Barents and White Seas we propose, for the first time, a possible route for the invasion of the Baltic Sea by M. arctia from the White Sea through the White Sea–Baltic Sea Canal. At the same time, our analysis of the sequences of COI fragments showed a significant genetic distance (p = 4.28–4.29%) between individuals identified as M. arctia from the Baltic, Barents and White Seas and those from the Kara Sea. This genetic distance, as well as the isolated estuarine habitats of these Arctic worms, and the large geographic distance between the type locality of M. arctia in the Beaufort Sea (Alaska) and northern Europe, raise doubts about the conspecificity of North American, North European and Northwest Pacific populations. We report M. neglecta for the first time for the British Isles (River Thames). We also review the evidence for the role of the Baltic Sea−Volga Canal and the Volga−Don Canal in facilitating the dispersal of M. neglecta to the Caspian Sea and the Sea of Azov, respectively. We further provide new insight on the phylogeny of Marenzelleria, an updated diagnosis of the genus and a key for morphological identification of Marenzelleria adults greater than 1.2 mm wide.

Fish assemblages in the Neckar River were investigated by electrofishing under the Water Framework Directive 2000/60/EC (WFD) to assess the ecological status of rivers. This monitoring program also provides information on the distribution of invasive Ponto-Caspian gobies along the Neckar River in Germany, a tributary of the Rhine River. The western tubenose goby Proterorhinus semilunaris was first recorded on the Neckar River in 2007, followed by bighead goby Ponticola kessleri and round goby Neogobius melanostomus in 2009 and 2012, respectively. The current distribution boundary for Ponto-Caspian gobies coincides with the navigation limit for cargo ships at the river port of Plochingen (about 200 km up­stream of the city of Mannheim). Marked differences in fish assemblages took place following invasion of the round goby, with average CPUE of native stone loach Barbatula barbatula and gudgeon Gobio gobio declining from 19.6 and 21.5 individuals per 100 m, respectively, to fewer than one. Bighead gobies failed to build up a stable stock after round goby invasion but have still been caught in small numbers at most sampling sections. The earlier-arriving western tubenose goby could not be detected any longer. The results indicate a strong impact of the round goby on native fish assemblages in the Neckar River which will hamper efforts to improve the ecological quality of the river. Further investigations are needed to assess long term effects of round goby invasion and find solutions for achieving the mandatory European Water Framework Directive (WFD) target of “good ecological status” of the river.

The monogenean freshwater parasite Gyrodactylus salaris Malmberg, 1957 is endemic to Atlantic salmon (Salmo salar) east of the Baltic Sea, but has spread outside this area via transport and stocking of fish. In Norway and Russia, infections with G. salaris have had catastrophic consequences for many salmon populations. The parasite is also common on farmed rainbow trout (Oncorhynchus mykiss) where it can persist in low numbers and without clinical signs. The transport and movement of infected rainbow trout is an important factor in the spreading of G. salaris in Europe. Due to increasing interest in establishing rainbow trout farms in White Sea drainages in Murmansky Oblast, Russia, and the potential subsequent unintentional spreading of G. salaris, parasitological examinations of salmonids were carried out. Farmed rainbow trout (n = 48) and Atlantic salmon (n = 375) from River Tuloma and farmed rainbow trout from Lake Imandra (n = 10), were examined in the period from 2015 to 2019. Additionally, environmental DNA monitoring was conducted for the detection of G. salaris in 2018. Gyrodactylus specimens were first detected in 2015 on Atlantic salmon from the tributary River Pak. Specimens obtained from Atlantic salmon in River Tuloma and from rainbow trout in River Tuloma and Lake Imandra the following years were confirmed to be G. salaris by sequencing of the nuclear ribosomal internal transcribed spacer (ITS rDNA) and mitochondrial cytochrome oxidase 1 (COI). All specimens carried the same COI sequence, which was identical to a strain (GenBank Accession number AF479750) frequently found on farmed rainbow trout. The prevalence varied, but reached 100% in some samples. Maximum intensity observed was 899, but intensities were generally lower than intensities expected to lead to mortalities. There was good correspondence between eDNA monitoring and conventional methods. The results indicate that G. salaris has spread to River Tuloma via transport of live rainbow trout.

Trophically-transmitted endoparasites can manipulate the behavior of intermediate hosts to increase transmission to definitive hosts. Less clear, however, is whether these relationships exist when parasites and hosts have limited coevolutionary history, e.g., a native parasite infecting an invasive host. We investigated infection by the northeastern North American trematode Microphallus similis in non-native green crabs (Carcinus maenas) to assess whether infection by M. similis influenced feeding behaviors in C. maenas and if this changed with time post-infection. We manipulated infection by randomly assigning crabs to parasite exposure and control groups. We then measured individual crab behavior at five time points (pre-infection, 72 h, 1 week, 2 week, and 3 week post-infection) with an established ethogram that recorded multiple behavioral types. We also conducted righting response trials at each time point and additionally at 4 and 5 weeks post-exposure. Compared to controls, infected crabs showed little difference in recorded behaviors, and burden of infection (i.e., number of trematode cysts) was not correlated to any behavioral metric. This lack of behavioral impact occurred at all stages of infection. Active parasite penetration/establishment early in the infection process did not provoke greater behavioral response than later stages, when the encysted parasite becomes relatively dormant. Although M. similis is capable of infecting non-native C. maenas, our results suggest that it does not manipulate host behavior, possibly because of limited coevolutionary history with C. maenas in the region, or because host manipulation is unnecessary for successful completion of its life cycle. In nature, this may have implications for the crab’s invasion success in the western Atlantic, where it has escaped much of its native parasite diversity.

Atractolytocestus huronensis Anthony, 1958 has been co-introduced with its cyprinid host Cyprinus carpio Linnaeus, 1758, common carp, to several continents. This cestode was only recently (2012) detected in South Africa and occur in two major river systems. In Africa, A. huronensis has only been reported from C. carpio. During routine parasitological surveys in the Vaal River system in central South Africa, unidentified cestodes were recorded from common carp at several localities. Using light and scanning electron microscopy, alongside genetic characterisation, they were identified as A. huronensis, greatly expanding the distribution of this parasite in the upper reaches of the Vaal River system and indicating rapid spread in the system. Thereafter, in November 2020, more caryophyllidean cestodes were detected infecting native smallmouth yellowfish, Labeobarbus aeneus (Burchell, 1822) just below the Vaal Dam wall. They were also morphologically and genetically identified as A. huronensis, indicating a possible new definitive host and spillover from carp. However, only juvenile worms (up to late stage 4) were detected in L. aeneus, suggesting a paradefinitive or accidental infection. Their pathological effect on the intestine of L. aeneus mimicked that described in acute infections in common carp, with damage limited to the intestinal epithelium and no prominent ulcerations. This apparent mild infection of an indigenous host needs to be monitored. The spillover to L. aeneus appears to be recent as no caryophyllidean cestodes were collected from this host species at the same locality and season the previous year, nor at any of the other well studied sites in the Vaal River system. Chronic infection of L. aeneus may still develop and indicate that the near threatened largemouth yellowfish, Labeobarbus kimberleyensis (Gilchrist & Thompson, 1913), may be at risk as well.

Mangrove forests worldwide have been subjected to biological invasion. Invasive apple snails (Pomacea canaliculata) have established populations in some mangrove forests. The feeding behavior of P. canaliculata in mangroves has been unclear until now. The feeding electivity of P. canaliculata to mangrove leaves, including leaves from Acanthus ilicifolius, Acrostichum aureum, Kandelia candel, Aegiceras corniculatum, and Sonneratia apetala, was studied through a selective test, a non-selective test, and a T-tube test. The growth indicators, the feeding ratio, the feeding rate, the feeding amount, the electivity indicator, and the electivity frequency were determined. The weight increase ratios of P. canaliculata that consumed leaves of A. ilicifolius and A. aureum were higher than those that consumed leaves of K. candel, S. apetala, and A. corniculatum. The electivity indicator showed that P. canaliculata preferred A. ilicifolius leaves and fed little on A. corniculatum leaves. Acrostichum aureum leaves were the second most preferred food for the apple snails. The feeding electivity of P. canaliculata to leaves from five species of mangrove trees was significantly differentiated by cluster analysis, redundancy analysis, and principal component analysis. Eight feeding indicators of the apple snails were positively correlated with the leaf characteristics of nitrogen content, protein content, leaf area, moisture content, and aspect ratio and negatively correlated with the lignin, phenolic, and tannin contents. Pomacea canaliculata could discriminate mangrove leaves through physical and chemical characteristics and shift feeding electivity among mangrove leaves under intraspecific competition. Mangrove forests composed mainly of A. ilicifolius and A. aureum might be at risk of invasion by P. canaliculata. A detailed survey on benthic animals is necessary to monitor and prevent P. canaliculata invasion in mangroves.

Recruitment is one of the most important dynamic rate functions (i.e., recruitment, growth, and mortality). Often, recruitment can be heavily dependent on overwinter survival. Wintertime presents thermal and metabolic challenges to fish. Studies have suggested that overwinter survival and mortality is correlated to lipid content before entering winter. Inadequate lipid reserves are related to poor condition and may lead to overwinter mortality. Young fish need to accumulate adequate lipid reserves before entering winter. In the Mississippi River, where silver carp Hypophthalmichthys moltrix Valenciennes, 1844 are hyper abundant, silver carp are not experiencing recruitment issues. As such, we evaluated lipid levels and size as potential silver carp recruitment regulators. Silver carp were collected by the Long Term Resource Monitoring element in 2015 on the middle Mississippi River using mini fyke nets; total lengths ranged from 34–177 mm. Lipid levels of whole carp were determined using the phosphovanillin assay. No difference in lipid levels (mg/g) was observed between spring and fall fishes. Additionally, we observed no relation between total length and lipid levels. Size structure did not significantly differ between fall age-0 and spring age-1 silver carp. Our results suggest there may not be a size dependent overwinter mortality/survival in silver carp in the middle Mississippi River. Additionally, lipids may not be a driving factor in overwinter mortality/survival. Our research suggests silver carp in the Mississippi River basin do not follow most early life history paradigms and may explain the successful nature of the silver carp invasion.