Mussel Mortality Research Articles

Genomic abnormalities affecting mussels (Mytilus edulis-galloprovincialis) in France are related to ongoing neoplastic processes, evidenced by dual flow cytometry and cell monolayer analyses

In the context of the abnormal mass mortality of mussels in France since 2014, Flow CytoMetry (FCM) was used in 2015 and 2016 to study the DNA content and cell cycle characteristics of hemic circulating cells collected from 2000 mussels. The mussels were sampled from 12 wild and cultivated blue mussels stocks distributed along the French Atlantic coast from the south Brittany to Pertuis Charentais areas. During these surveys, various genetic abnormalities were frequently detected, and ploidy characteristics revealed contrasting profiles that corresponded to respective contrasting sanitary status, i.e. healthy mussels with high cytogenetic quality (HCQ) versus diseased mussels with low cytogenetic quality (LCQ). In the present work, FCM and hemocytology cell monolayer techniques were combined in order to determine the putative causes of the observed genetic abnormalities that were significantly associated with mortality levels. FCM and cell monolayer approaches permitted the definition of new threshold values delimiting HCQ mussels from LCQ ones. FCM histograms of mussels from the HCQ group showed one single or a largely dominant population of diploid (2n) nuclei and a large majority of normal hemocytes. Hemolymph cell-monolayer analyses showed predominantly acidophil granulocytes characterized by nuclei of normal size and a large cytoplasm with numerous granulations. In contrast, FCM histograms for the LCQ group showed, in addition to the normal diploid (2n) nuclei, populations of nuclei that displayed aneuploidy patterns in a broad ploidy range, including diploid-triploid (2-3n), tetraploid-pentaploid (4-5n) and heptaploid-octaploid levels (7-8n). The corresponding hemolymph cell-monolayer showed cellular features characteristic of disseminated neoplasia disease with frequent abnormal anaplastic cells that exhibited noticeable numbers of mitotic figures with both normal and aberrant chromosomes segregation patterns. These neoplastic cells were a rounded shape with a reduced, granulation-free cytoplasm and large (11-12 µm) to very large (up to 21 µm) round or ovoid nuclei that correspond to the 4-5n and 7-8n nuclei previously detected by FCM analyses. These characteristics suggest that the genetic abnormalities detected by means of FCM were related to an ongoing neoplastic process that is affecting blue mussels in France, at least since the onset in 2014 of the mortality that heavily impacted French blue mussels stocks.

Effects of erosion-accretion processes on a community dominated by Brachidontes rodriguezii (Mollusca: Mytilidae) on a rocky outcrop of the South Atlantic coast

Abstract Strong winds are powerful modifiers of coastal areas, altering sedimentary balance on sandy beaches and causing either loss (erosion) or gain (accretion) of sediment. Sand inundations can impact intertidal organisms by smothering or scouring and also affect community development and organization. The rocky outcrop where the mussel bed of Brachidontes rodriguezii develops is exposed to sand burial disturbance. To investigate the effect of this disturbance on the mussel population and its associated community, seasonal sampling was carried out on two adjacent areas within a rocky outcrop, one less exposed (A1) to sand disturbance than the other (A2). The seasonal variation in the area of the mussel bed was estimated using GPS. Biological samples were taken from A1 and A2 and additional samples were taken from buried and unburied sites in A2. In addition, a microcosm experiment was designed to assess the effect of burial duration on mussel behaviour and mortality. Local data on wind speed and direction were obtained and analyzed in relation to changes in the rocky outcrop areas. The erosive period was associated with strong, persistent winds whereas during the period of accretion no such wind events were recorded. The gain of sediment was associated with a higher reduction in the mussel bed area in A2. The mussel population in A1 showed a higher abundance and recruitment percentage, and organisms reached a larger size. Diversity was also higher in A1 but only during the erosive period. Mussel mortality was higher for buried than unburied samples while richness and dominance were higher in unburied samples. During the microcosm experiment, mussel mortality was higher in buried trials than in the controls and the inability of the species to emerge from the buried trial was also observed. This underlines the importance of sand dynamics for the mussel bed community.

Haplosporidium pinnae sp. nov., a haplosporidan parasite associated with mass mortalities of the fan mussel, Pinna nobilis, in the Western Mediterranean Sea.

This study provides morphological and molecular characterization of a new species, Haplosporidium pinnae), very likely responsible for mass mortality of fan mussels, Pinna nobilis, in the Western Mediterranean Sea. The parasite was found in dead or moribund P. nobilis but did not occur in healthy fan mussels from locations that were not affected by abnormal mortality. Histological examination of infected fan mussels showed uninucleate cells of a haplosporidan parasite throughout the connective tissue and hemolymph sinuses of the visceral mass and binucleate cells and, rarely, multinucleate plasmodia were also detected in the connective tissue. Additionally, stages of sporulation occurred in the epithelium of the host digestive gland tubules. Spores were slightly ellipsoidal with a hinged operculum in one pole. Typical haplosporosomes were not found with TEM but vesicles with two concentric membranes resembling haplosporosomes were abundant in the cytoplasm of the multinucleate plasmodia occurring in host digestive gland tubules. SEM analysis showed multiple structures on the spore surface; some spores had two or four long tape-like filaments attached to the spore wall. Phylogenetic analysis based on the SSU rDNA sequence placed this parasite within a large clade including species of the order Haplosporida, not in the Bonamia/Minchinia subclade or the subclade containing most Haplosporidium species, but within a subclade of Haplosporidium sp. from Penaeus vannamei. Our results suggested that H. pinnae and the parasite of P. vannamei may represent a distinct new genus within the order Haplosporida.

Mortality investigation of Mytilus edulis and Mytilus galloprovincialis in France: An experimental survey under laboratory conditions

In the context of mass mortality outbreaks affecting adult and juvenile mussels since 2014 in France, two investigations were conducted to study mussel mortality under laboratory conditions in 2015. The first investigated the horizontal transmission of a putative causal agent of the mortality among two stocks of wild Mytilus edulis and the potential genetic resistance of adults and their progenies. The second evaluated the resistance of pure and hybrid crosses of M. edulis and M. galloprovincialis at the spat stage to a mortality outbreak. For the first time in France, we described several mortality outbreaks affecting spat and adult mussels under laboratory conditions. Mortality was observed for seawater temperatures ranging from 10 to 23 °C, although the significant mortality outbreaks occurred between 12 and 17 °C in adults and at 22 °C in spat. The disease screening revealed that no notifiable pathogen agent, as defined by OIE, was detected in the analyzed moribund mussels. Although bacteria belonging to the Splendidus clade were detected at high prevalence, with the exception of a mortality outbreak occurring in August, their role could not be defined in this study. Survivors of a mortality event occurring in the field in 2014 (Yves stock) still exhibited around 30% of mortality in 2015 under laboratory conditions, which indicated that they were either not fully resistant or that susceptibility varies with mussel age/size. This finding also suggests that a part of the survivors (or all) were carriers of a putative causal agent of the mortality. We demonstrated the horizontal transmission of a putative causal agent from the Yves stock to another stock of wild adult mussels (stock Agnas) which experienced 46% of mortality. In contrast, the Agnas stock had low mortality (5%) in the separate condition. Horizontal transmission of a putative causal agent from the wild adults to their hatchery-produced progenies was also observed. The progenies of the Yves stock, which survived a mortality outbreak in 2014, had lower mortality (27%) than those of the unselected Agnas stock (68%). Similarly, low mortality (<20%) were reported at the spat stage for a second stock of M. edulis produced from survivors of a mortality outbreak as well as for M. galloprovincialis, whereas their interspecific hybrids had mortality around 30%. These results could suggest that selective breeding programs in M. edulis, or the cultivation of M. galloprovincialis rather than M. edulis, could both reduce the impact of mortality outbreaks on mussel aquaculture. Nevertheless, further investigations are required to address the genetic basis of the survival in the two main mussels species cultivated in France.

Impacts of sea star predation on mussel bed restoration

Predation by sea stars has the potential to cause elevated levels of mortality in reestablished populations of bivalves relative to levels of recruitment. Recent efforts to restore beds of the nearly extirpated green‐lipped mussel within the Hauraki Gulf, New Zealand, resulted in high abundances of sea stars occupying those beds and it is unknown whether predation poses a potential limitation to the success of restoration in this bivalve species. The contribution of predation by sea stars to the mortality of mussels across four experimental mussel beds over a 2‐year period was estimated using data from regular assessments of sea star abundance and an experimentally determined consumption rate of sea stars upon mussels. In addition, the potential size selection of mussels by sea stars was assessed to determine if large sea stars selected for recent settlers. Sea stars' abundance within the mussel beds grew to an average of 0.57 sea stars/m2 within 9 months, remaining at similar levels throughout the study. These predominantly large sea stars were estimated to have consumed 30.1% of the mussels over a 25‐month period, representing a contribution of 40.4% of the mussel mortality. Sea stars predominantly selected for larger mussels, and their predation likely contributes little to any lack in mussel recruitment. Sea star predation is clearly a limiting factor on the survival of transplanted adult mussels and the present study highlights the need to continually assess predation risk to determine if remediation is necessary for the persistence of the restored beds.

Toxicity of Potassium Chloride Compared to Sodium Chloride for Zebra Mussel Decontamination

The use of chemicals to decontaminate watercraft and/or equipment after exposure to zebra mussels Dreissena polymorpha is one method of decontamination that has been recommended by multiple government agencies in the United States. The ideal chemical to be used for decontamination would be inexpensive and easily obtained, would have no or limited effect on nontarget species, and would be relatively environmentally friendly. Two chemicals that have been tested are potassium chloride (KCl) and sodium chloride (NaCl). The toxicity of each chemical to both adult zebra mussels and veliger larvae was examined. Sodium chloride was less effective at causing mortality than KCl within the exposure periods tested. Adult mussels required a 4× longer exposure period to exhibit complete mortality when exposed to NaCl at 30,000mg/L (24h) compared to KCl (6h). At 10,000mg/L, NaCl took 8× longer (96h) than KCl (12h) to cause 100% mortality of adult mussels. Veligers that were exposed to KCl at 1,250mg/L required a 12-h exposure to attain complete mortality, while those exposed to NaCl at 10,000mg/L required an 18-h exposure to exhibit the same result. To determine whether KCl is more advantageous as a decontamination chemical, the cost and chemical availability must be researched.

Assessment of the effects of sulfated polysaccharides extracted from the red seaweed Irish moss Chondrus crispus on the immune-stimulant activity in mussels Mytilus spp.

Seaweeds contain a number of health enhancing and antimicrobial bioactive compounds including sulfated polysaccharides (SP). In the present study, SP extracted from a European red seaweed Irish moss Chondrus crispus was chemically analyzed, SP content extracted and the immune-response effect on wild Irish mussels Mytilus spp. investigated for the first time. A high percent yield of SP was extracted from C. crispus and the immune-stimulant activity of SP was assessed in a laboratory trial with mussels exposed to three different treatments of low (10 μg mL−1), medium (20 μg mL−1) and high (50 μg mL−1) SP dose concentrations and a control mussel group with no exposure to SP. An initial mussel sample was processed prior to the trial commencing and mussels were subsequently sampled on Days 1, 2, 3, 4, 7, and 10 post SP exposure. Both cell, humoral and immune related gene responses including haemocyte cell viability, haemocyte counts, lysozyme activity and expression of immune related genes (defensin, mytimycin and lysozyme mRNA) were assessed. No mussel mortalities were observed in either the treated or non-treated groups. Mussels exposed with SP showed an increase in haemocyte cell viability and the total number of haemocytes compared to control mussels. Lysozyme activity was also higher in treated mussels. Additionally, up-regulated expression of defensin, mytimycin and lysozyme mRNA was observed in SP treated mussels shortly after exposure (on Days 1, 2, and 3) to SP. These results indicate that a high quality yield of SP can be readily extracted from C. crispus and more importantly based on the animal model used in this study, SP extracted from C. crispus can rapidly induce health enhancing activities in Mytilus spp. at a cellular, humoral and molecular level and with a prolonged effect up to ten days post treatment.

The red macroalga Gracilaria verrucosa in co-culture with the Mediterranean mussels Mytilus galloprovincialis: productivity and nutrient removal performance

The feasibility of integrating seaweed cultivation with mussel culture in Bizerte lagoon (north Tunisia) was investigated during 1 year, in order to exploit mussel excretion nutrients as resource input and to reduce the risk of eutrophication. In parallel, to evaluate nutrients’ biofiltering efficiency and uptake rates of the agarophyte Gracilaria verrucosa, growth and nutrient removal from mussel culture water were investigated. In the laboratory, seaweed/mussel co-culture experiments were compared to mussel monoculture systems. The results showed that nitrogen and phosphorus concentrations in monoculture were significantly higher than those in co-culture treatments. Algal growth rate, thallus nutrient contents, and mussel mortality were different between all treatments. The mussel/seaweed biomass ratio of 1:0.28 (treatment 1) was convenient for efficient nutrient uptake and best seaweed growth. Field cultivation trials showed that G. verrucosa grew well in bivalve culturing farm in Bizerte lagoon at a maximum growth rate of 4.45% day−1 attained in spring season. The mean nitrogen content in dry thalli cultured in co-culture with mussel in Bizerte lagoon was 4.19 ± 0.81%. Results indicate that G. verrucosa can efficiently absorb the nutrients from mussel in Bizerte lagoon and can be associated with local mussel farms, mitigating eutrophication, and eventually, increasing economic incomes of farmers.

Toxicity of Potassium Chloride Compared to Sodium Chloride for Zebra Mussel Decontamination

Decontamination of watercraft and/or equipment following exposure to zebra mussels with the use of chemicals is one method of decontamination that has been recommended in the United States by multiple government agencies. The ideal chemical to be used for decontamination would be inexpensive, easily obtained, have no or limited effect on nontarget species, and relatively environmentally friendly. Two chemicals that have been tested are potassium chloride and sodium chloride. The toxicity of each chemical to both adult mussels and veliger larvae was examined. Sodium chloride was less effective at causing mortality than potassium chloride within the exposure periods tested. Adult mussels required an exposure period four times longer to experience complete mortality when exposed to sodium chloride (24h) at a concentration of 30,000mg/L compared to potassium chloride (6h). At a 10,000mg/L concentration, sodium chloride took eight times longer (96h) to cause 100% mortality of adult mussels than potassium chloride (12h). Veligers exposed to 1,250mg/L of potassium choride required a 12h exposure period to cause complete mortality while an exposure period of 18h was required for a 10,000mg/L concentration of sodium chloride to have the same result. To determine if potassium chloride is more advantageous as a decontamination chemical, the cost and chemical availability need to be researched. Received 30 May 2017 accepted 01 Oct 2017 revised 12 Sep 2017.

Can crabs kill like a keystone predator? A field-test of the effects of crab predation on mussel mortality on a northeast Pacific rocky shore.

Predation can strongly influence community structure and ecosystem function, so the loss of key predators can have dramatic ecological consequences, unless other predatory species in the system are capable of playing similar ecological roles. In light of the recent outbreak of sea star wasting disease (SSWD) and subsequent depletion of west coast sea star populations, including those of the keystone predator Pisaster ochraceus, we examined whether large mobile crabs could play a role as predators on mussels (Mytilus californianus) on a rocky shore in Northern California. Using a combination of sea star removal and predator exclusion cages we found that mussel mortality was 43–294 times greater in uncaged treatments versus caged treatments. Mortality on uncaged mussels at low tidal elevations was due to predation by large mobile crabs (Cancer productus and Romaleon antennarium); confirmed by the presence of mussel shell fragments and documented attacks on wax snail replicas. Laboratory feeding assays indicated that crabs, on a per unit biomass basis, can consume almost twenty-five times as many mussels per day than sea stars, which together with the results of our field experiment, suggest that large predatory crabs could play an important role in maintaining ecosystem function through their predation on mussels on rocky shores where P. ochraceus are rare, absent, or have been depleted by SSWD.

Variability in early post-settlement mortality in intertidal mussels and the role of size at settlement

ABSTRACTEarly post-settlement mortality is difficult to measure in mobile benthic taxa such as mussels. Field studies typically employ settlement collectors that often contain empty shells of dead individuals, which are usually disregarded. Here, empty shells of pediveligers, i.e. recent settlers that died before beginning to grow as juveniles, were used to assess temporal and spatial patterns of early mortality in mussels, whether size at settlement determined mortality, and whether mortality was density-dependent. This study took place at two intertidal sites in a large harbour in central New Zealand where monthly cohorts of mussels were collected over a 2-year period. Monthly mortality varied substantially, ranging from 0% to 42.6%, but not across the two sites that were 27 km apart. Although there was no density-dependent mortality evident within cohorts, the proportion of pediveligers which were dead on collection was highly positively correlated across sites. Live settlers were on average larger than dead settlers, and the size distribution of dead settlers was shifted toward smaller sizes compared to live settlers. At the extremes, of all settlers with shell length of 260 µm or less, 72% were dead on collection. By contrast, for settlers 310 µm or greater in length, 6% were dead. Together, these results (1) suggest that in this system size at settlement may be an important determinant of very early, peri-metamorphic mortality in mussels, with smaller settlers at higher risk, and (2) demonstrate the value in evaluating dead pediveligers for assessing natural early post-settlement mortality in mussels.

Environmental conditions increase growth rates and mortality of zebra mussels (Dreissena polymorpha) along the southern invasion front in North America

Environmental conditions found along an invasion front can mediate spread dynamics of an invasive species. Conditions that affect survival and individual growth rates of founder propagules and the first young-of-year generation can have a profound effect on establishment dynamics. Responses of younger, more sensitive individuals to these novel conditions, in part, determine establishment success. The southern invasion front of zebra mussels in North America expanded into Texas in 2009. To determine mechanisms that could affect establishment of zebra mussel populations at low latitudes in North America, an in situ study was conducted in Lake Texoma, on the Texas-Oklahoma border. Survival and growth were measured of young-of-year juveniles at multiple sites within the reservoir. Age-specific mortality was significantly positively correlated with temperature at all sites and no mortality occurred when temperatures were <26 °C. Shell-length growth rates were the highest ever reported for lentic environments. A decrease in shell-length growth rates was associated with an increase in soft tissue mass, possibly resulting from flexible energy allocation from shell development to gametogenesis after maturation. Overall, survivorship and growth were related to water temperatures and chlorophyll-a concentrations. Warm waters found at lower latitudes along the invasion front could facilitate establishment of populations by increasing growth rates and decreasing time to maturity. However, due to extreme climate events (e.g. drought and flooding) and a strong temperature-mortality relationship, mortality likely will also be high beyond the southern invasion front, resulting in highly dynamic boom and bust cycles.

Potential environmental drivers of a regional blue mussel mass mortality event (winter of 2014, Breton Sound, France)

In the context of global change, increasing mariculture production has raised particular concerns regarding its environmental impact and sustainability. Molluscs and particularly blue mussel account for a significant part of this total production. Although blue mussels are considered to be pretty resilient to environmental disturbances, we report in this study an unprecedented mussel mortality event that occurred during the winter of 2014 in the Breton Sound. 9000metrictonnes of mussels were lost and mortality rates up to 100% were recorded at some farming areas. Through a coupling approach, the present work aims to better understand the potential environmental drivers associated with those mortalities. Firstly, we analysed long-term in situ and satellite data from environmental monitoring networks (available since 1998) to characterize the variability of seawater masses of the sound during the winter of 2014. Secondly, we used modelling simulations to study the possible relationship between seawater hydrodynamics and observed spatio-temporal patterns of mussel mortalities. From January to April 2014 at the long-line culture site where mortalities started, seawater temperatures ranged from 8.3 to 13.3°C (10.2±0.8°C). Salinity and turbidity values showed successive and short drops (below 16; 29.3±2.3) and numerous peaks (above 70 NTU; 17.4±13.4 NTU) respectively. Winter conditions of 2014 were encountered along the entire French Atlantic coastline and linked to the sixth highest positive North Atlantic Oscillation (NAO+) index recorded since 1865. These particular environmental variations characterized the winter of 2014 but also others whereas no comparable mussel mortality rates were reported. Exact causes of the 2014 mortality event are still unknown but we showed these environmental variations could not alone be responsible. These have likely affected the sensitivity of the blue mussel populations that were already weakened by early spawning. Meanwhile, these may have facilitated the apparition of a pathogenic strain of Vibrio splendidus isolated on moribund mussels at that time. Our modelling simulations suggested that this pathogenic strain could spread through hydrodynamic patterns and drive the observed mussel mortalities. If this pathogenic strain recurs in future years, particularly with the added stress associated with climate change, mussel mass mortality events may exceed the resilience of this species.

Isolation of Vibrionaceae from wild blue mussel (Mytilus edulis) adults and their impact on blue mussel larviculture.

The blue mussel (Mytilus edulis) is known as a robust bivalve species, although its larviculture appears to be highly susceptible to diseases. In this study, we isolated 17 strains from induced mortality events in healthy wild-caught blue mussel adults and demonstrated that they caused between 17% and 98% mortality in blue mussel larvae in a newly developed, highly controlled immersion challenge test model. Eight of the isolates belong to the Splendidus clade of vibrios, while the other isolates belong to the genus Photobacterium. The genomes of the most virulent Vibrio isolate and the most virulent Photobacterium isolate were sequenced and contained several genes encoding factors that have previously been linked to virulence towards bivalves. In vitro tests confirmed that all 17 isolates were positive for these virulence factors. The sequenced genomes also contained a remarkably high number of multidrug resistance genes. We therefore assessed the sensitivity of all isolates to a broad range of antibiotics and found that there were indeed many strong positive correlations between the sensitivities of the isolates to different antibiotics. Our data provide an ecological insight into mass mortality in blue mussels as they indicate that wild mussels contain a reservoir of pathogenic bacteria.

Simulated mussel mortality thresholds as a function of mussel biomass and nutrient loading.

A freshwater “mussel mortality threshold” was explored as a function of porewater ammonium (NH4+) concentration, mussel biomass, and total nitrogen (N) utilizing a numerical model calibrated with data from mesocosms with and without mussels. A mortality threshold of 2 mg-N L−1 porewater NH4+ was selected based on a study that estimated 100% mortality of juvenile Lampsilis mussels exposed to 1.9 mg-N L−1 NH4+ in equilibrium with 0.18 mg-N L−1 NH3. At the highest simulated mussel biomass (560 g m−2) and the lowest simulated influent water “food” concentration (0.1 mg-N L−1), the porewater NH4+ concentration after a 2,160 h timespan without mussels was 0.5 mg-N L−1 compared to 2.25 mg-N L−1 with mussels. Continuing these simulations while varying mussel biomass and N content yielded a mortality threshold contour that was essentially linear which contradicted the non-linear and non-monotonic relationship suggested by Strayer (2014). Our model suggests that mussels spatially focus nutrients from the overlying water to the sediments as evidenced by elevated porewater NH4+ in mesocosms with mussels. However, our previous work and the model utilized here show elevated concentrations of nitrite and nitrate in overlying waters as an indirect consequence of mussel activity. Even when the simulated overlying water food availability was quite low, the mortality threshold was reached at a mussel biomass of about 480 g m−2. At a food concentration of 10 mg-N L−1, the mortality threshold was reached at a biomass of about 250 g m−2. Our model suggests the mortality threshold for juvenile Lampsilis species could be exceeded at low mussel biomass if exposed for even a short time to the highly elevated total N loadings endemic to the agricultural Midwest.

Physiological effects of biocide on marine bivalve blue mussels in context prevent macrofouling

Mussels are stubborn organisms attached to solid substrata by means of byssus threads. The abundance of marine mussel Mytilus edulis in marine facilities like power stations was reason to select among fouling animals. Mortality patterns as well as physiological behavior (oxygen consumption, foot activity, and byssus thread production) of two different size groups (14- and 25-mm shell length) of M. edulis were studied at different hydrogen peroxide concentrations (1–4 mg l−1). Studied mussels showed progressive reduction in physiological activities as the hydrogen peroxide concentration increased. Mussel mortality was tested in 30 days exposure, and 14 mm mussels reached the highest percentage of 90% while 25 mm mussels reached 81%. Produced data was echoed by Chick-Watson model extracted equation. This study points that, while it could affect the mussel mortality moderately in its low concentrations, hydrogen peroxide has a strong influence on mussels’ physiological activities related to colonization. Therefore, hydrogen peroxide can be an alternative for preventing mussel colonization on facilities of marine environment.

Assessing the hydrogen peroxide effect along with sodium hypochlorite against marine blue mussels aimed at antifouling usage

Chlorination has been the most common antifouling method, but alternatives are under searching. In this article, we report how the hydrogen peroxide could enhance the effect of chlorination to prevent fouling by inhibiting larvae settlement and abatement of mussel colonization or by extinct of them; through marine mussel Mytilus edulis. The addition of hydrogen peroxide shows synergic effect on the veliger larvae (up to 19 folds) and effectively reduces required time of mussel mortality by 8-22%. For resolution of micro- and macro-fouling caused by the marine mussel, as well as diminishing of time and conventional chlorine dose could be important factor in favour of environment and economics.

Effects of carbon dioxide on juveniles of the freshwater mussel (Lampsilis siliquoidea [Unionidae]).

Carbon dioxide (CO2 ) has shown promise as a tool to control movements of invasive Asian carp, but its effects on native freshwater biota have not been well studied. The authors evaluated lethal and sublethal responses of juvenile fatmucket (Lampsilis siliquoidea) mussels to CO2 at levels (43-269 mg/L, mean concentration) that bracket concentrations effective for deterring carp movement. The 28-d lethal concentration to 50% of the mussels was 87.0 mg/L (95% confidence interval [CI] 78.4-95.9) and at 16-d postexposure, 76.0 mg/L (95% CI 62.9-90.3). A proportional hazards regression model predicted that juveniles could not survive CO2 concentrations >160 mg/L for more than 2 wk or >100 mg/L CO2 for more than 30 d. Mean shell growth was significantly lower for mussels that survived CO2 treatments. Growth during the postexposure period did not differ among treatments, indicating recovery of the mussels. Also, CO2 caused shell pitting and erosion. Behavioral effects of CO2 included movement of mussels to the substrate surface and narcotization at the highest concentrations. Mussels in the 110 mg/L mean CO2 treatment had the most movements in the first 3 d of exposure. If CO2 is infused continuously as a fish deterrent, concentrations <76 mg/L are recommended to prevent juvenile mussel mortality and shell damage. Mussels may survive and recover from brief exposure to higher concentrations. Environ Toxicol Chem 2017;36:671-681. Published 2016 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Enhanced surveillance of shellfish mortality to improve early detection and investigation of outbreaks of exotic or emerging infectious diseases: An example of a mass mortality outbreak of mussels, France 2014

This paper explores the relevance and feasibility of enhanced surveillance of mussel-related mortality based on regular telephone interviews of a key informant in a farming community. Based on qualitative analyses of data collected through semi-structured interviews, this method of participatory disease surveillance enabled the retrieval of high quality data during an outbreak of mussel mortality which occurred in Pertuis Charentais, France, in 2014.The findings illustrated that such an enhanced surveillance approach compared with the institutional shellfish health surveillance system could improve the early detection of outbreaks of mussel mortality by one week. This approach enabled a detailed description of the outbreak, showing higher incidence proportion in the Northern water bodies. It also captured relevant data for hypothesis generation for further outbreak investigations, integrating a global view of the health and disturbance of the coastal marine ecosystem. However, to be effective and sustainable, this flexible approach requires a pre-existing knowledge of the structure of the information network of the farmers’ community. Such a community-based enhanced surveillance could increase the reactivity of the entire system to enable the earliest possible and most appropriate interventions to protect shellfish populations against exotic or emerging infectious diseases. This would also help to improve the vigilance of mussel farmers and foster their commitment, which is an essential element for sustainable shellfish health surveillance.

Multilocus sequence analysis of Vibrio splendidus related-strains isolated from blue mussel Mytilus sp. during mortality events

One of the most widely European farmed mollusc, the mussel Mytilus sp., has been subjected to massive mortalities located in Charente-Maritime (France) in spring 2014. The national surveillance network for mollusc health has reported a systematic detection of V. splendidus in all dying batches. V. splendidus is the type species of a clade composed of almost 20 known strains with variable pathogenicity on bivalves. In our study, we first developed a Multi Locus Sequence Analysis (MLSA), specific to V. splendidus group, based on fragments of 5 housekeeping genes: atpA, ftsZ, mreB, rpoD and topA. This tool was validated on reference strains and compared with individual gene analyses. It allowed a useful and reliable classification of V. splendidus closely-related strains. Thanks to MLSA, we then tried to classify genetically 23 strains isolated from healthy or dying mussels. 21 were classified within the Splendidus clade: in splendidus cluster (38%), in tasmaniensis cluster (24%), in artabrorum cluster (24%) and on distinct branches (14%). All of them were tested by injection to healthy adult mussels to identify possible pathogenic strains. Experimental trials revealed the presence of a strain called M3H, allied with the splendidus cluster and able to induce mortality in mussels with rates up to 80%. The M3H virulence was demonstrated by the recovery of the injected strain in dying animals, resulting from repeated experimental infections. Further work should be now conducted to explore the pathogenicity of the M3H strain towards different mussel batches and under various conditions. Statement of relevanceOur MLSA is useful to identify related V. splendidus strains