Mytilopsis Leucophaeata Research Articles

Matching field-based ranges in brackish water gradients with experimentally derived salinity tolerances of Conrad’s false mussel (Mytilopsis leucophaeata cochleata) and zebra mussel (Dreissena polymorpha)

The invasive alien false mussels Mytilopsis leucophaeata cochleata and Dreissena polymorpha (Dreissenidae) have established populations in the North Sea canal in the Netherlands that connects the harbours of Amsterdam with the North Sea. The favourable and unfavourable salinity ranges of both species were earlier studied in long-term outdoor mesocosm experiments. Their occurrence in salinity gradients in estuaries or canals connecting seaways to freshwater harbours provides information on their salinity tolerance under field conditions. By the combination of laboratory experiments and field data using the same source population a high predictability can be expected for establishment of the gradients facilitated by constructions. The reliability of experimentally derived salinity-tolerance limits for both dreissenid species was tested using data on their distribution in a salinity gradient of the littoral zone along the North Sea canal. The mussels used for the survival experiments in mesocosms were also collected from this canal. Favourable salinity ranges for adult survival in the mesocosms were 0.2 – 17.5 for M. leucophaeata cochleata and 0.2 – 6.0 for D. polymorpha. Unfavourable salinities were outside these ranges and led to high and fast mortality of these species. Mytilopsis leucophaeata cochleata was present over nearly the whole length of the North Sea canal with the highest densities close to the sea sluices where also the highest salinities and water temperatures were measured. Their densities in the canal decreased gradually at larger distances from the sea. Dreissena polymorpha co-exists with M. leucophaeata cochleata at the east end of the canal with low salinity due to the influence of freshwater of the river Rhine. The occurrence of D. polymorpha was restricted to a salinity below 4 and M. leucophaeata cochleata only occurred at a salinity above 1.5 (maximum value measured in the canal 9.2). Shorter salinity gradients with lower salinity ranges provided additional information on the co-existence of both species. Co-existence was observed at a salinity range of 1.5–3.3 (own data), 1.0–3.5 (Van Couwelaar and Van Dijk 1989), both in the North Sea canal, and 0.2–2.8, in the Canal through Voorne (Janssen and Janssen-Kruit 1967). These data correspond with studies of both species by Walton (1996) in the Hudson River (salinity range 0–3). Found salinity ranges in the North Sea canal for both species match with the tolerance results obtained by mesocosm experiments. A new invading dreissenid mussel Dreissena rostriformis bugensis and a mytilid Ischadium recurvum occur in the North Sea canal since 2006 and 2012, respectively. Competition between recent and earlier invaders is likely when salinity tolerances are similar. It has already been observed that D. rostriformis bugensis outcompetes D. polymorpha under freshwater conditions (Bij de Vaate et al. 2014; Matthews et al. 2014). Ischadium recurvum has the potential to colonize large parts of the canal and to be a strong competitor of M. leucophaeata cochleata (Goud et al. 2019). Since January 2022, the new ‘Zeesluis IJmuiden’ with the biggest locks in the world is in use, affecting the probability of population establishment of new introduced and invasive alien mussel species.

First Record of Microplastic Contamination in the Non-Native Dark False Mussel Mytilopsis leucophaeata (Bivalvia: Dreissenidae) in a Coastal Urban Lagoon.

Microplastic contamination is a global concern due to its conspicuous presence in aquatic ecosystems and its toxic nature to environmental and human health. False mussels are among the most notable fresh- and brackish water invaders. The invasive Mytilopsis leucophaeata in Rodrigo de Freitas Lagoon-RFL (Rio de Janeiro, Brazil) is the most abundant macrofaunal invertebrate, widely established and distributed throughout the lagoon. This study aimed to assess microplastic contamination in this invasive filter feeder and evaluate its potential use as a bioindicator. Agglomerates (~100 mussels) were manually collected using a stainless-steel spatula in ten sampling areas distributed throughout the whole lagoon and kept frozen. In the laboratory, 60 individuals were sorted by area for soft-tissue digestion. Each pool of 10 soft-tissue mussels (n = 6 by area) was wet-weighted and then placed in a 150-mL decontaminated glass beaker with 50 mL of 10% KOH. Samples were heated (40 °C) for 48 h, and digested samples were filtered in glass-fiber membranes. Microplastics were found in all samples of mussels (n = 60) from RFL; the particles were mostly lower than 100 µm with a mean concentration (±SD) of 35.96 ± 47.64 MPs g wet-weight-1. Microplastics were distinguished in seven shapes with different occurrences in samples (%): fiber (43.3%); fragment (34.3%); film (16.3%); sponge/foam (4.9%); pellet (0.57%), rope/filaments (0.17%); and undefined (0.4%). Thirteen colors of microplastics were found, but transparent (54.94%), black (10.77%), and white (9.36%) were the most common. Mytilopsis leucophaeata were useful to assess microplastic contamination in RFL and might be preferentially used in other invaded brackish systems instead of native and often threatened bivalves. Our results confirm the effective application of bivalves as an indicator of coastal microplastic pollution.

Do feeding responses of a non-native bivalve outperform the native one in a coastal lagoon? A possible explanation for the invasion success of the dark false mussel Mytilopsis leucophaeata.

The present study aimed to evaluate and compare feeding responses of the non-native and native bivalves, the dark false mussel Mytilopsis leucophaeata and the scorched mussel Brachidontes darwinianus, respectively, by offering different concentrations of seston from the coastal lagoon where these species coexist after dark false mussel introduction (Rodrigo de Freitas Lagoon, Rio de Janeiro-Brazil). For this purpose, independent laboratory experiments were carried out under five concentrations of seston to test the differences in clearance and ingestion rates of bivalves as a function of increasing concentrations of suspended particulate matter (SPM) on seston. In addition, from the integrated analysis of data obtained in experiments, it can be inferred about the efficiency levels of these species to remove SPM from seston and their effects on water turbidity and nutrient concentrations (total carbon, nitrogen, and phosphorus). Our hypothesis was that the non-native bivalve is more efficient to clear and ingest SPM from seston compared to the native one, which may lead to competitive advantages to the successful invasion of M. leucophaeata in coastal lagoons. Native species did not show a significant difference in clearance and ingestion rates with increasing concentrations of seston. Whereas the non-native bivalve showed a slight tendency to increase its clearance and ingestion rates with the increase in seston concentrations, evidencing its plasticity to adjust its feeding responses. The native bivalve was significantly more efficient to clear and ingest SPM at the lower seston concentration (i.e., close to natural concentrations found in the lagoon) compared to the non-native bivalve, which, on the other hand, showed a significant increase in its ingestion rates at the higher concentration tested (140 mg SPM L-1). Thus, the present results did not suggest food competition between the non-native M. leucophaeata and the native B. darwinianus in the introduced system. However, M. leucophaeata increased its feeding response with experimental increment in seston concentration, which suggests species ability to benefit from conditions of increased inputs of organic matter and higher primary production that could mediate its establishment in introduced systems.

Host and transmission route of Enterocytozoon hepatopenaei (EHP) between dragonfly and shrimp

Enterocytozoon hepatopenaei (EHP) is a shrimp pathogen that causes huge economic losses. In the present study, the hosts of EHP were investigated using polymerase chain reaction (PCR) in an aquaculture farm located in Maoming, China. EHP was detected in Litopenaeus vannamei, Penaeus monodon, Varuna litterata, Mytilopsis leucophaeata, and three dragonfly species (Anax parthenope, Pantala flavescens, and Ischnura senegalensis). In the histopathological examination using hematoxylin–eosin (HE) staining, EHP spores were found in nymphs and adult dragonflies naturally infected with EHP that were collected from the shrimp farm. Fluorescence in situ hybridization (FISH) results showed a positive signal for EHP infection in the fat body of dragonfly nymphs. Immature and mature microsporidian spores and late sporogonial plasmodium were observed in the cytoplasm of dragonfly nymphs using transmission electron microscopy (TEM). The transmission of EHP from shrimp to dragonfly nymphs was confirmed via cohabitation challenge experiments in which EHP-free dragonfly nymphs were cohabited with EHP-infected shrimp, and the transmission of EHP from dragonfly nymphs to shrimp was demonstrated via the cohabitation of EHP-infected dragonfly nymphs with EHP-free shrimp and oral administration challenge experiments. This study confirms that dragonflies can act as natural EHP hosts, and a novel EHP horizontal transmission route exists between dragonflies and shrimp.

Hypereutrophic conditions limit the removal of suspended particulate matter by the invasive bivalve Mytilopsis leucophaeata (Conrad, 1831) (Dreissenidae)

Hypereutrophic conditions limit the removal of suspended particulate matter by the invasive bivalve Mytilopsis leucophaeata (Conrad, 1831) (Dreissenidae)

Mais um lugar para chamar de casa: o bivalve invasor Mytilopsis leucophaeata alcança o sistema lagunar Maricá-Guarapina (Rio de Janeiro, Brasil)

Abstract Mytilopsis leucophaeata is an estuarine bivalve native from the Gulf of Mexico and Southeast USA, and it was introduced in Europe, Asia, Caribbean, South America and Northeast USA, showing massive colonization skills. In Brazil, the single invasion records of M. leucophaeata occur in the city of Rio de Janeiro, i.e., in the Rodrigo de Freitas Lagoon and in the Marapendi Lagoon. We conducted a new series of fieldworks in estuaries from the Rio de Janeiro state in order to evaluate the propagation of this invasive bivalve, aiming sites with proper salinities for the establishment of M. leucophaeata. A new record is given for the Maricá-Guarapina lagoon system, where M. leucophaeata mainly colonizes hard substrata (such as piers and rocks), reaching a mean density up to 43,375 specimens/m2; however, aggregates of M. leucophaeata were also observed in the soft substratum. Based on mitochondrial sequences, the taxonomic identification of the invasive bivalve was confirmed. The associated fauna to the agglomerates of M. leucophaeata in the lagoon system comprises amphipods, barnacles, tanaidaceans, isopods, crabs, polychaetes and snails. The expansion of M. leucophaeata requires a continuous investigation due to the great circulation of boats in the littoral of the Rio de Janeiro state and the increased chance of new introductions.

False mussels (Mytilopsis leucophaeata) can be mechanical carriers of the shrimp microsporidian Enterocytozoon hepatopenaei (EHP)

Enterocytozoon hepatopenaei (EHP) is an obligate intracellular parasite causing hepatopancreatic microsporidiosis (HPM) in cultivated shrimp in Asian countries. One strategy to control EHP is to identify and eliminate biological reservoir(s) in shrimp ponds. Several marine and brackish-water organisms, including false mussels (Mytilopsis) have been reported to test positive for EHP using the PCR method. Thus, we tested Thai false mussel Mytilopsis leucophaeata collected from the 6 ponds with EHP-infected shrimp for the presence of EHP using SWP-PCR. Results revealed the sampled mussels from all 6 ponds were PCR positive. Subsequent bioassays were carried out to study EHP transmission between mussels and shrimp. Firstly, the naïve mussels were cohabitated with EHP-infected shrimp and all mussels were SWP-PCR positive at day 20 post cohabitation. One batch of such PCR-positive mussels was transferred for cohabitation with naïve shrimp and 37.5% EHP-positive shrimp were observed within 10 days. Tissue analysis of the SWP-PCR-positive mussels using light microscopy, in situ hybridization technique and electron microscopy did not confirm EHP infection. In summary, there was no evidence demonstrating that Mytilopsis leucophaeata was itself infected with EHP. However, the false mussels were apparently capable of carrying infectious spores for some period after ingestion and serving as a mechanical or passive carrier. The results support previous reports warning of the danger of feeding living or fresh bivalves to broodstock shrimp in hatcheries or shrimp in rearing ponds without prior heating or freezing.

Marine bioinvasions: bivalve molluscs introduced in northeast Brazil

ABSTRACT: Invasive alien species are those that, once introduced from other environments, adapt, starting to reproduce and proliferate in places they did not previously inhabit. The introduction of exotic marine species as a result of anthropic activity, whether intentionally or not, is a process that has been remote for centuries, which makes it difficult to assess the impact of these activities, making studies that address the status of knowledge about such organisms always important. Thus, this research aims to gather information about bivalve molluscs introduced into marine ecosystems in northeastern Brazil, in addition to discussing the knowledge of this invasive fauna for the Northeast, Southeast and South regions of Brazil. For that there was a search for bibliography in 5 databases - SciELO, Web of Science, Google Scholar, ScienceResearch.com and I3N Brazil Database of the Horus Institute for Environmental Conservation and Development. Three invasive bivalves for the northeastern region of Brazil were counted. When compared to the South and Southeast regions, the Northeast presents a significant amount of research on the ecology of the species Isognomon bicolor (C. B. Adams, 1845) and Mytilopsis leucophaeata (Conrad, 1831), which is very important, because with these results it is possible to track and understand the pathways that make bioinvasions possible. Regarding Perna Perna (Linnaeus, 1758), although there is a discussion about its supposed introduction in Brazilian waters, the species can be considered invasive in Northeastern Brazil.
 KEYWORDS: Invasive species, marine ecosystem, ecology.

Benthic macrofauna associated to the invasive bivalve Mytilopsis leucophaeata (Dreissenidae) in a coastal lagoon in Rio de Janeiro, Brazil.

The invasion record for the estuarine bivalve Mytilopsis leucophaeata in Brazil is in Rio de Janeiro city, including the Rodrigo de Freitas Lagoon, where high densities of this invader were registered. This work aimed to (1) assess the composition and structure of the benthic macrofauna associated with this invader in Rodrigo de Freitas Lagoon, (2) analyze the spatiotemporal variation of richness, density and diversity of the associated benthic community, and (3) correlate changes on the density of the associated benthic species with some water quality variables and the density of M. leucophaeata. Clusters of M. leucophaeata were collected monthly (two years) in four sites. Nine taxa associated with M. leucophaeata were found; Heleobia sp. (Gastropoda) and Melita mangrovi (Amphipoda) showed the highest densities. The structure of the benthic macrofauna slightly differed among sampling sites, but not between dry and wet seasons. The water quality parameters, specific patterns of each taxon and high densities of M. leucophaeata contribute to variations in density of the associated species. Oscillations in the densities of M. leucophaeata and the native bivalve Brachidontes darwinianus suggest some agonistic relationship between them, such as a competition for space.

Population Dynamics and Secondary Production of the Invasive Bivalve Mytilopsis leucophaeata (Bivalvia, Dreissenidae) in Lagoa Rodrigo De Freitas, Rio De Janeiro, Brazil

The dark false mussel Mytilopsis leucophaeata is an invasive bivalve known from two locations in Rio de Janeiro (Brazil): Lagoa Rodrigo de Freitas and Lagoa de Marapendi. For a population biology study of this species, monthly collections were carried out at Lagoa Rodrigo de Freitas over a period of 2 y (March 2016–March 2018). High densities were registered in both studied years: 84,560 (±22,066) ind. m–2 in the first year and 65,848 (±7,830) in the second year. Growth was lower for the first year (K = 0.4 for year 1 and K = 0.8 for year 2), whereas seasonal oscillation (C = 0.6) was of the same intensity in both years. The period of lower growth differed for the years, occurring in June (WP = 0.5) in the first year and in August (WP = 0.7) in the second year. The maximum and asymptotic lengths, longevity, secondary production, biomass, and turnover rate were higher for the first year; on the other hand, mortality was higher at the second year. Density of the invasive mussel was significantly and positively related with salinity (r2 = 0.5547; P < 0.0001). In a general way, the second year of study seems to be a more adverse period for the population of the invasive mussel with reduced density, body sizes, life expectancy, secondary production, biomass, and higher mortality. Among environmental factors, salinity seems to exert the strongest influence on the regulation of population attributes.

Shell Mass, Biomass, Condition, and Reproductive State of the Invasive Bivalve Mytilopsis leucophaeata (Conrad, 1831) (Dreissenidae)

Basic information on shell dimensions, calcimass and periostracum mass, biomass, and the relation between the condition and reproduction of Mytilopsis leucophaeata was analyzed for a population in the North Sea Canal, the Netherlands. The mean dry flesh weight of individuals with a mean shell length of 12.5 mm showed a peak at the end of June. The mussel reached the highest mean dry flesh weight in the month before the spatfall started. The gonad index (GI) was high in June, followed by a period of decrease until September and a period of increase until November. The condition index (CI) peaked in June and decreased during the remainder part of the year. The range of CI was highest in May when the gonadal development progressed and was smallest in June when the gonadal development was complete. The CI decreased during the rest of the year. Quantile regressions showed a highly significant relation between CI and shell length. Based on the regression coefficients, the CI was maximal at a shell length of 11.4 mm and minimal at 12.5 mm. Condition index variation was highest within a shell length range of 10–15 mm.

Are invasive species always negative to aquatic ecosystem services? The role of dark false mussel for water quality improvement in a multi-impacted urban coastal lagoon

The dark false mussel Mytilopsis leucophaeata occurs as non-native species in Asia, Europe and South America. Despite the low population density usually found in its native range, M. leucophaeata forms dense clusters in newly invaded areas which lead to impacts on local organisms and environment. Some of the impacts of non-native species on newly colonized areas may be positive. However, despite the empirical evidences of increase in water transparency by freshwater dresseinids, the hypothesis that dark false mussel enhances the quality of brackish water has never been tested so far. Thus, the present study aimed to determine M. leucophaeata impacts on the water quality of a nutrient-enriched coastal lagoon by (1) analyzing a historical water dataset for pre- and post-invasion at Rodrigo de Freitas Lagoon (Brazil) and (2) experimentally testing dark false mussel direct effects on water quality. Historical field data evidenced significant lower phytoplankton abundance and chlorophyll a, and higher water transparency for the post-invasion period. These pattens were also supported by time-series analyses, which detected a decreasing trend for total coliforms density and an increased trend for dissolved oxygen over time. Moreover, time series indicated a gradual increase in lagoon water level with time, but none or minor changes were evidenced for floodgates operation routine, meteorological variables, and the frequency of sewage input. In microcosms, M. leucophaeata was effective to increase water transparency and decrease E. coli densities. The combination of field and laboratory data partially supported the hypothesis that M. leucophaeata invasion promoted an improvement in lagoon water quality, but increased phosphorus availability through excretion in microcosm assays. Management of dark false mussel populations seems to be a potential strategy for water quality improvement within already invaded systems where high sewage-enriched effluents are released. However, as non-native species often unbalance ecological relationships and functioning of the invaded ecosystems, new introductions of M. leucophaeata must be avoided.

The spreading of the invasive bivalve Mytilopsis leucophaeata (Dreissenidae) into estuaries of Rio de Janeiro, Brazil.

An extensive field survey was conducted to evaluate the spreading of the invasive estuarine bivalve Mytilopsis leucophaeata into the metropolitan region of Rio de Janeiro (Brazil), in which the single invaded site so far recorded is Rodrigo de Freitas Lagoon. A novel record is made to the Marapendi coastal lagoon, where M. leucophaeata mainly colonizes mangrove roots. A reef composed of druses above the unconsolidated substratum is recorded for the first time for this species. The fauna associated to agglomerates of M. leucophaeata was composed of eight taxa: polychaetes Alitta succinea and Polydora sp., amphipods Melita mangrovi and Elasmopus sp., barnacles Amphibalanus eburneus and A. improvisus, the crab Eurypanopeus cf. dissimilis and the gastropod Heleobia spp. Based on COI sequences, the haplotype diversity of M. leucophaeata invasion in Marapendi Lagoon is high, like that previously recorded in Rodrigo de Freitas Lagoon. The expansion of M. leucophaeata demands a continuous investigation, including the knowledge of its impacts on the biota.

New Alien Species Mytilopsis Leucophaeata and Corbicula Fluminalis (Mollusca, Bivalvia) Recorded in Georgia and Notes on Other Non-Indigenous Molluscs Invaded the South Caucasus

Abstract First records of invasive bivalve freshwater mollusc species Mytilopsis leucophaeata (Conrad, 1831) and Corbicula fluminalis (O. F. Müller, 1774) in Georgia are reported. No native or alien extant dreissenid species have ever been recorded form this region so far. A finding of C. fluminalis in Georgia is also a new record for the country though this species inhabits the rivers of adjacent Azerbaijan. Apart from two mentioned bivalve molluscs three non-indigenous gastropod species are registered from Georgia: freshwater Ferrisia californica (Rowell, 1863) and Physella acuta (Draparnaud, 1805) and land snail Eobania vermiculata (O. F. Müller, 1774).

Invasion of the dark false mussel in shrimp farms in Venezuela: species identification and genetic analysis

Invasion of the dark false mussel in shrimp farms in Venezuela: species identification and genetic analysis

Growth, Survival, and Mortality of Juvenile and Adult Alien Conrad's False MusselMytilopsis leucophaeata(Conrad, 1831) (Mollusca, Bivalvia, Dreissenidae) in a Brackish Canal

The false mussel, Mytilopsis leucophaeata originating from the Atlantic coast and Gulf of Mexico in North America invaded brackish water systems in Europe. Seasonal sessile population structure is determined by spat fall, growth, and mortality. Juvenile and adult M. leucophaeata were kept in cages in a brackish water canal to study their mortality and to estimate annual and seasonal shell growth rate in relation to shell size and water temperature. Mortality increased with increasing temperature with the strongest effect on the 4–6 mm and 8–10 mm size classes. The average mortality of all size classes of M. leucophaeata in cage experiments was lowest in winter, increased from April to July, and peaked in July and August. Between a water temperature of 18 and 23°C, a strong growth was observed for mussels of size classes 2–14 mm, whereas mussels of size class 14–16 mm showed only a slight growth (<20 µm day-1) and size classes 16–18 mm and 18–22 mm showed no growth at all. When water temperature was between 9 and 18°C, there was no or slight growth, and at lower than 9°C, hardly any growth. Especially for the small mussels, the influence of the water temperature on shell growth is strong. Polynomial regression showed a mean summer growth rate of 94 µm day-1 for the 2–4 mm class, 37 µm day-1 for the 10–12 mm class, and no growth for the 18–22mmclass. Analysis of all available (literature) data yielded mean summer and annual growth rates of M. leucophaeata collected in brackish western European harbors and canals ranging from 30 to 133 µm day-1 and 8 to 49 µm day-1, respectively. Increase of water temperature by climate change or thermal discharges will increase growth rates and mortality of this mussel.

EDNA for detection of five highly invasive molluscs. A case study in urban rivers from the Iberian Peninsula.

Biological invasions are an important threat to biodiversity especially in aquatic ecosystems, and their frequency is generally higher near urban areas. Potentially invasive non-indigenous molluscs were deliberately introduced into European waters for food (Corbicula fluminea) and biocontrol (Melanoides tuberculata), and unintentionally introduced by ballast water (Mytilopsis leucophaeata, Corbicula fluminea), stock contamination (Sinanodonta woodiana), accidental escapes from aquaculture (Sinanodonta woodiana), aquarium trade releases (Melanoides tuberculata) and even attached to aquatic birds (Corbicula fluminea). Three rivers from the Iberian Peninsula were monitored near the three most populated inland cities to evaluate the presence of these invasive molluscs through PCR amplification using taxon-specific primers from eDNA. New primers were designed within 16S rRNA and cytochrome oxidase subunit I genes, tested in silico from BLAST methodology and experimentally in vitro before application in the field. C. fluminea was found in Ebro River (near Zaragoza); M. leucophaeata in Guadalquivir River (near Sevilla). M. tuberculata and S. woodiana were found from enclosed areas (lake and reservoir respectively) upstream, respectively, Zaragoza and Madrid. The new tools are ready to be used in other regions where these species are also invasive.

Settlement, Seasonal Size Distribution, and Growth of the Invasive BivalveMytilopsis leucophaeata(Conrad, 1831) (Dreissenidae) in Relation to Environmental Factors

ABSTRACT Conrad's false mussel (Mytilopsis leucophaeata) is an invasive alien bivalve species causing severe biofouling problems in cooling water systems of power and industrial plants. Settlement, seasonal shell size distribution, and growth of this bivalve species were analyzed in relation to relevant environmental factors, using monitoring data from a brackish canal over a period of 4 y. Salinity at the sampling site ranged from3.2 to 9.2,water temperature from 4.5°C to 23.9°C, and chlorophyll a content from 2 to 56 µg l-1. Once a month one short-term exposed panel (1mo exposed) and one long-term exposed panel (exposed from February 1989 to the month of sampling) were collected. Settled spat and attached mussels were collected monthly from these polyvinylchloride panels and from stones in the littoral zone. The short-term exposed panels were used to determine the period of spat fall. The long-term panels were used to study growth, shell length-frequency distribution, and densities of the mussel populat...

Dark False Mussel,Mytilopsis leucophaeata(Bivalvia: Dreissenidae), in the Lower West River, New Haven, New Haven County, Connecticut

In October 2015, the dark false mussel, Mytilopsis leucophaeata, was encountered in the Duck Pond of the West River at Edgewood Park in New Haven, New Haven County, Connecticut, USA. The natural endemic range of Mytilopsis leucophaeata is the Gulf of Mexico and the temperate Atlantic coast of North America from Tampico, Mexico, northward to the Chesapeake Bay. In the late 1930s, Mytilopsis leucophaeata became established in the Hudson River basin in New York. The only previous reports of Mytilopsis leucophaeata from New England are from the Charles River near Boston, Massachusetts, in 1981 and from the Housatonic River in Fairfield County, Connecticut, in the 1990s. Mytilopsis leucophaeata has been characterized as the brackish-water equivalent to the zebra mussel, Dreissena polymorpha, and has been associated with severe fouling problems of water-cooling systems in Europe where it has been introduced. It is hypothesized that Mytilopsis leucophaeata was introduced by ballast water of ships from New Haven Harbor and established in the lower West River subsequent to the installation of two-way tidal gates in the course of a tidal marsh and channel restoration project completed in 2012. Other invertebrates collected were the hydrozoan Cordylophora caspia; the polychaetes Hobsonia florida and Polydora cf. ciliata; the amphipods Gammarus fasciatus and Apocorophium simile; the ivory barnacle, Amphibalanus eburneus; and Say's mud crab, Dyspanopeus sayi. The blue crab, Callinectes sapidus, was commonly observed. The freshwater leech, Helobdella modesta, which was once abundant in the Duck Pond, was not collected. Given the invasive potential of Mytilopsis leucophaeata, in conjunction with the paucity of knowledge of many aspects of its natural history, especially in introduced settings, it is important to monitor this population.

Salinity as a barrier for ship hull-related dispersal and invasiveness of dreissenid and mytilid bivalves.

The benthic stages of Dreissenidae and Mytilidae may be dispersed over long distances while attached to ship hulls. Alternatively, larvae may be transported by water currents and in the ballast and bilge water of ships and vessels. To gain insight into dispersal potential and habitat suitability, survival of the benthic stages of two invasive dreissenid species (Dreissena polymorpha and Mytilopsis leucophaeata) and one mytilid species (Mytilus edulis) chosen based on their occurrence in fresh, brackish and sea water, respectively, were tested in relation to salinity. They were exposed to various salinities in mesocosms during three long-term experiments at outdoor temperatures. Mussel survival was studied without prior acclimation, reflecting conditions experienced when attached to ship hulls while travelling along a salinity gradient from fresh or brackish water to sea water, or vice versa. Initially, mussels react to salinity shock by temporarily closing their valves, suspending ventilation and feeding. However, this cannot be maintained for long periods and adaptation to higher salinity must eventually occur. Bivalve survival was monitored till the last specimen of a test cohort died. The results of the experiments allowed us to distinguish favorable (f.: high tolerance) and unfavorable (u.: no or low tolerance) salinity ranges in practical salinity units (PSU) for each species, viz. for D. polymorpha 0.2–6.0 PSU (f.), 7.0–30.0 PSU (u.), for M. leucophaeata 0.2–17.5 PSU (f.), 20.0–30.0 PSU (u.) and for M. edulis 10.5–36.0 PSU (f.), 0.2–9.0 and 40 PSU (u.). At the unfavorable salinities, all mussels died within 14 days of initial exposure with the exception of M. edulis (23–30 days). The maximum duration of survival of single specimens of D. polymorpha was 318 days at a salinity of 3.2 PSU, of M. leucophaeata 781 days at 15.0 PSU and of M. edulis 1052 days at 15.0 PSU. The number of days survived was compared with the duration of actual ship voyages to estimate the real world survival potentials of species dependent of salinity changes, travel distances and durations. The conclusion is that salinity shocks during the trip were survived within the favorable salinity range but that the species tolerate only for a few weeks the unfavorable salinity range. This functions as a barrier for dispersal. However, at faster and more frequent shipping in the future salinity can become no longer very important as a dispersal barrier.