Adult Mussels Research Articles

Rare earth elements and warming: Implications for adult mussel health and sperm quality

The present study aimed to investigate the effects of europium (Eu) exposure (10 μg/L), warming (a 4 °C increase), and their combination on Mytilus galloprovincialis. Biochemical and histopathological changes in adult mussels were evaluated after a 28-day exposure period. Additionally, biochemical and physiological alterations in sperm were measured following a 30-min exposure period. The overall responses to each treatment were assessed using the Integrated Biological Response index version 2 (IBRv2). In adult mussels, warming elevated metabolism and activated glutathione S-transferases (GSTs), leading to redox imbalance and cellular damage. Europium exposure alone slightly enhanced metabolism and GSTs activity, resulting in cellular damage and histopathological injuries in digestive tubules. The combined exposure to Eu and warming was the most detrimental treatment for adults, as indicated by the highest IBRv2 value. This treatment slightly increased metabolism and uniquely elevated the activity of antioxidant enzymes, as well as GSTs and carboxylesterases. Despite these responses, they were inadequate to prevent redox imbalance, cellular damage, and histopathological injuries in digestive tubules and gills. Regarding sperm, warming reduced reactive oxygen species (ROS) production but raised lipid peroxidation levels. Sperm exposed to this treatment also increased their oxygen consumption and exhibited reduced velocity. The IBRv2 indicated that Eu was the most harmful treatment for sperm, significantly increasing ROS production and notably decreasing sperm velocity. When combined with warming, Eu elevated superoxide anion (O2-) production, lowered sperm velocity, and increased oxygen consumption. This study underscores the importance of investigating the effects of rare earth elements and their interaction with climate change-related factors.

Predicting key ectotherm population mortality in response to dynamic marine heatwaves: A Bayesian‐enhanced thermal tolerance landscape approach

Abstract As climate change intensifies heatwaves, quantifying associated mortality within ectothermic populations is crucial for effective conservation. Thermal tolerance landscape (TTL) models are useful predictive tools that assume exponentially decreasing survival durations in individuals with increasing temperatures. This assumption has been validated through regression analyses on data from constant temperature experiments, primarily focusing on adult‐stage individuals. However, this approach does not allow for direct model validation with data from dynamic, real‐world heatwave events and overlooks early recruitment stage vulnerabilities. This study aimed to address these gaps using the blue mussel Mytilus, a foundation species forming extensive reefs along temperate coasts, as a model organism. We monitored survival rates of mussels (juveniles and adults) under constant heatwave (CHW) conditions in a laboratory experiment and under dynamic heatwave (DHW) scenarios simulated in an outdoor mesocosm experiment. Post‐heatwaves, we also assessed recruitment rates within the mesocosms. TTL models were parametrised by employing Approximate Bayesian Computation with Sequential Monte Carlo (ABC‐SMC) on each dataset separately. The parameter distributions were similar across both experiments, and the ABC‐SMC model predictions closely matched the observed survival declines, validating these models. In comparison, we found a lower predictive performance when using a Bayesian regression approach. Additionally, our best‐fit model predicted that warming across the non‐fatal DHW regimes would increase sublethal effects on mussels. The observed impact on the recruitment stage was more pronounced, with the recruitment rate following an exponential decay as sublethal effects increased. Our model projected minor (<4%) sublethal effects in adult mussels during the century's five warmest summer temperature regimes, corresponding to 0%–32% declines in recruitment rates. Our research extends the TTL model validation, demonstrates the resilience of subtidal Baltic Mytilus to future extreme heatwaves and offers an approach to predict heatwave‐induced population mortalities, applicable to other species and sensitive systems. Read the free Plain Language Summary for this article on the Journal blog.

Praseodymium and warming interactions in mussels: Comparison between observed and predicted results

Being a crucial element for technological development, praseodymium (Pr) has been increasingly used, leading to a rise in its concentration in aquatic systems. However, its potential threats to organisms remain poorly understood. Besides contamination, organisms are also threatened by climate change-related factors, including warming. It is important to evaluate how climate change-related factors may influence the effects of contaminants. To address this, histopathological and biochemical analyses were performed in adult mussels of Mytilus galloprovincialis, following a 28-day exposure to Pr (10 μg/L) and warming (4 °C increase) separately, and in combination. Additionally, biochemical and physiological alterations were analysed in the sperm of mussels after 30-min exposure to the same treatments. Furthermore, it was used the Independent Action model to predict the interaction between Pr and warming. The results showed, in the case of adults exposed to Pr, an increase in superoxide dismutase (SOD) and glutathione S-transferases (GSTs) activities. However, it was insufficient, leading to histopathological injuries, redox imbalance, and cellular damage. In the case of sperm, Pr induced an increase of mitochondrial activity and respiration rate, in response to the increase in systemic metabolic rate and oxygen demand. Warming increased the metabolism, and induced redox imbalance and cellular damage in adults. In sperm, a rise in temperature induced lipid peroxidation and a decrease in velocity. Warming induced some alterations in how adult mussels responded to Pr, activating catalase instead of SOD, and in addition to GSTs, also activated carboxylesterases. However, it was not enough to avoid redox imbalance and cellular damage. In the case of sperm, the combination induced a decrease in H2O2 production, and higher oxygen demand, which prevented the decrease in motility and velocity. This study highlights the limitations of using models and emphasizes the importance of studying the impacts of emerging contaminants, such as rare earth elements, and their combination with climate change-related factors. Under environmental conditions, chronic exposure to the combined effect of different stressors might generate impacts at higher biological levels. This may affect organisms' respiratory and filtration capacity, nutrient absorption, defence capacity against infections or diseases, and sperm viability, ultimately resulting in reduced growth and reproduction, with consequences at the population level.

Acute Toxicity of the Lampricide 4-Nitro-3-(trifluoromethyl)phenol to the Mussel (Obovaria subrotunda), Its Host (Percina maculata), and a Surrogate Mussel Species (Obovaria olivaria).

The risk of lampricide applications (such as 4-nitro-3-[trifluoromethyl]phenol [TFM]) to nontarget fauna continues to be a concern within the Great Lakes Fishery Commission Sea Lamprey Control Program, especially among imperiled aquatic species-such as native freshwater mussels. The Grand River (Ohio, USA) is routinely treated for larval sea lampreys (Petromyzon marinus), and this river contains populations of the federally threatened mussel Obovaria subrotunda. Given this spatial overlap, information on the sensitivity of O. subrotunda to TFM is needed. Our objectives were to assess the toxicity of TFM to (1) adult Obovaria olivaria (a surrogate for O. subrotunda), (2) glochidial larvae of O. olivaria and O. subrotunda, (3) juveniles of O. olivaria and O. subrotunda, and (4) adult Percina maculata (host for O. subrotunda glochidia). In acute toxicity tests, TFM was not toxic to glochidia and adult mussels at exposure concentrations that exceed typical treatment rates. Although significant dose-response relationships were observed in hosts and juveniles, survival was ≥95% (Percina maculata), ≥93% (O. olivaria), and ≥74% (O. subrotunda) at typical treatment rates. However, the steep slope of these dose-response relationships indicates that an approximately 20% difference in the treatment level can result in nearly an order of magnitude difference in survival. Collectively, these data indicate that routine sea lamprey control operations are unlikely to acutely affect these species or their host. However, given that many mussel species are long-lived (30-100 years), the risks posed by lampricide treatments in the Great Lakes would be further informed by research on the potential long-term effects of lampricides on imperiled species. Environ Toxicol Chem 2024;43:1423-1430. Published 2024. This article is a U.S. Government work and is in the public domain in the USA.

Responses of native freshwater mussels to remediation to remove polychlorinated biphenyl‐contaminated sediments in the upper Hudson River

Abstract The Hudson River, New York, was contaminated with polychlorinated biphenyls (PCBs) from two manufacturing plants over a period of approximately 30 years, and PCBs are still present in sediment and biota today. The river provides habitat for a variety of plants and animals, including native freshwater mussels. A remediation programme, consisting of dredging followed by the placement of backfilled sediment and/or a subaqueous cap, was initiated in 2009 to remove PCB‐contaminated sediments, and managers were concerned about how remediation could affect the mussels. Quantitative surveys were conducted across nine reaches (pools) to estimate species composition, density, population size, population structure, and ecosystem services of mussel assemblages, pre‐ and post‐remediation. Surveys were stratified into remediated areas (targeted for dredging) and non‐remediated areas (not targeted for dredging). Pre‐remediation, the river contained a low diversity, and high, but variable, density of mussels that were strongly dominated by Elliptio complanata. The presence of few fresh dead mussels indicates low natural mortality. Frequent recruitment by many species, varied length classes, and high biomass also support robust assemblages that perform important ecosystem services, such as biofiltration. Remedial activity removed most of the mussels and the associated services that they perform: their density was reduced by 83% and their filtration capacity was reduced by 93%, relative to non‐remediated areas. Areas that were remediated were almost devoid of adult mussels, but the presence of small mussels indicates that natural recolonization is occurring. However, it is unknown whether these assemblages will persist. As mussels are generally long lived and slow growing, natural recovery is anticipated to be slow, in the order of decades.

Habitat suitability of Unionidae host fish in the Rhine Delta

Unionid populations are declining worldwide as they are threatened by anthropogenic habitat alterations, the introduction of invasive alien species and the effects of climate change. Several studies have focused on the habitat preferences of adult mussels but none to date have reported on the importance of the habitat preferences of host fish species. The aim of this study was to determine the habitat preferences of unionid host fish species in the Netherlands, to examine potential differences between native and alien host fish species, and to evaluate the effect of alien host fish species on unionid dispersal. Species sensitivity distributions (SSDs) were constructed for the range of occurrences and laboratory tolerance of host fish species in the Netherlands for water temperature, substrate type, flow velocity, and water depth. A case study was selected to assess the suitability to substrate type, flow velocity and water depth of a novel river habitat along longitudinal training dams in the river Waal. Unionid host fish species in the Netherlands preferred shallow littoral zones (0.1 m) with low flow velocity (0.05 m/s), an average water temperature of the Rhine delta (15°C), and most substrate types (ranging from silt to cobbles). Boulder substrate was the most limiting factor of the abiotic factors assessed for both native and alien host fish species. Management options for unionid populations should include host fish species in their assessments while focusing on creating and maintaining areas with limited boulders and implementing alien host fish species removal measures.

Investigating the effect of bacterial coinfections on juvenile and adult green‐lipped mussels (Perna canaliculus)

AbstractThe New Zealand's Greenshell™ mussel (Perna canaliculus) aquaculture industry is being affected by summer mortality events associated with increasing seawater temperatures and pathogens. In this study, challenge experiments were conducted to investigate, for the first time, the effects of pathogen coinfection on the survivability and haemolymph immune responses of juvenile and adult mussels. Animals were injected with marine broth (control), Vibrio mediterranei, Photobacterium swingsii, or a mixture of V. mediterranei and P. swingsii. Then, mussel survival was monitored for 72 h, and haemolymph was sampled for bacterial quantification and metabolomics analyses at 24‐ and 48‐h post challenge. Coinfected adults and juveniles showed 100% mortality. Bacterial colony counts in haemolymph decreased as infection time continued, especially in juveniles. The haemolymph metabolome of mussels exposed to single bacterial species and coinfection showed response changes largely within energy metabolism. Mussels infected with V. mediterranei exhibited increased metabolites linked to the glutathione pathway, branched‐chain amino acids, and others over time, supporting structural functions. Conversely, mussels infected with P. swingsii showed no metabolic differences over time. The coinfection group exhibited large decreases in important metabolites, such as fatty acids as an alternative energy source and amino acids to support immune functions and protein synthesis.

Examination of the effects of highly diluted bioactive compounds on gametogenesis in relation to energy budget and oocyte quality in mussel (Modiolus capax) broodstock

A critical bottleneck for bivalve hatcheries is the availability of mature broodstock with high-quality gametes to ensure the production of healthy spat. The use of highly diluted bioactive compounds (HDBC) has emerged as a novel and prophylactic strategy to improve gonad development, reproduction bioenergetics, and oocyte quality of marine bivalve broodstock. This study evaluates the effect of HDBC formulas to enhance the laboratory-controlled breeding capacity of Modiolus capax adult mussel, selected as a model organism because of its aquaculture potential as an alternative seafood resource. The experimental design included three replicates of three HDBC treatments at 31Centesimal (1 × 10−31) dynamizations using distilled water as the final excipient (TR1: SiT, CaS, HeS; TR2: PhA, FeP, ZnP; and TR3: ViP, ViA, ViT), and two control treatments: C+ hydro-alcoholic solution at 1% (Usual HDBC vehicle) and C- (distilled water) during a 30-day period. As a result, TR1 enhanced energy reserves (lipids and carbohydrates) in all tissues; TR2 promoted an increase in lipid and carbohydrate content in the gonad and their transfer into developing oocytes; TR3 significantly improved gonad development and reproductive capacity of the mussels with the highest proliferation of mature oocytes, enhancing food-nutrient assimilation and energetic reserve transfer from the somatic tissues to the ovary. Additionally, all HDBC formulas recorded a lower (P < 0.05) number of atretic oocytes compared to the untreated animals. This evidence reflects a simultaneous improvement of gametogenesis and energy budget of M. capax broodstock, ensuring sexual maturation and higher-quality oocytes when HDBC are used.

The effect of simulated marine heatwaves on green-lipped mussels, Perna canaliculus: A near-natural experimental approach

Marine heatwaves (MHW) are projected for the foreseeable future, affecting aquaculture species, such as the New Zealand green-lipped mussel (Perna canaliculus). Thermal stress alters mussel physiology highlighting the adaptive capacity that allows survival in the face of heatwaves. Within this study, adult mussels were subjected to three different seawater temperature regimes: 1) low (sustained 18 °C), 2) medium MHW (18–24 °C, using a +1 °C per week ramp) and 3) high MHW (18–24 °C, using a +2 °C per week ramp). Sampling was performed over 11 weeks to establish the effects of temperature on P. canaliculus survival, condition, specific immune response parameters, and the haemolymph metabolome. A transient 25.5–26.5 °C exposure resulted in 61 % mortality, with surviving animals showing a metabolic adjustment within aerobic energy production, enabling the activation of molecular defence mechanisms. Utilisation of immune functions were seen within the cytology results where temperature stress affected the percentage of superoxide-positive haemocytes and haemocyte counts. From the metabolomics results an increase in antioxidant metabolites were seen in the high MHW survivors, possibly to counteract molecular damage. In the high MHW exposure group, mussels utilised anaerobic metabolism in conjunction with aerobic metabolism to produce energy, to uphold biological functions and survival. The effect of exposure time was mainly seen on very long-, and long chain fatty acids, with increases observed at weeks seven and eight. These changes were likely due to the membrane storage functions of fatty acids, with decreases at week eleven attributed to energy metabolism functions. This study supports the use of integrated analytical tools to investigate the response of marine organisms to heatwaves. Indeed, specific metabolic pathways and cellular markers are now highlighted for future investigations aimed at targeted measures. This research contributes to a larger program aimed to identify resilient mussel traits and support aquaculture management.

Antidepressants and their metabolites primarily affect lysosomal functions in the marine mussel, Mytilus galloprovincialis

Antidepressants widely occur as emerging contaminants in marine coastal waters, with concentrations reported in the low ng/L range. Although at relatively lower levels with respect to other pharmaceuticals, antidepressants – fluoxetine (FLX) in particular - have attracted attention because of their striking effects exerted at low doses on marine invertebrates. In this study, the effects of four antidepressants including FLX, sertraline (SER), and citalopram, as members of the selective serotonin reuptake inhibitor (SSRI) class, and venlafaxine (VEN) as a member of the serotonin and norepinephrine reuptake inhibitor (SNRI) class, were evaluated in the mussel Mytilus galloprovincialis. In addition, the effects of two main metabolites of FLX and VEN, i.e., norfluoxetine (NFL) and O-desmethylvenlafaxine (ODV) respectively, were compared to those of the parent compounds. Eight concentrations of each drug (0.5–500 ng/L range) were tested on the early life stage endpoints of gamete fertilization and larval development at 48 h post fertilization (hpf). Egg fertilization was reduced by all compounds, except for VEN. Larval development at 48 hpf was affected by all SSRIs, but not by SNRIs. The above effects were significant but never exceeded 20 % of control values. Adult mussels were exposed in vivo for 7 days to environmental concentrations of the drugs (0.5, 5, and 10 ng/L) and a battery of eight biomarkers was assessed. Antidepressants primarily targeted lysosomal functions, decreasing haemocyte lysosome membrane stability (up to 70 % reduction) and increasing of the lysosome/cytosol ratio (up to 220 %), neutral lipid (up to 230 %), and lipofuscin (up to 440 %) accumulation in digestive gland. Only SER and NFL significantly affected catalase and glutathione-S-transferase activities in gills and digestive gland. NFL and ODV, were effective and sometimes more active than the parent compounds. All compounds impaired mussel health status, as indicated by the low to high stress levels assigned using the Mussel Expert System.

Potential to produce brown mussel integrated to a net-cage fish farm in a Mediterranean bay

In this study, we investigated the potential exploitation of the brown mussel Perna perna (Linnaeus, 1758) in an aquaculture farm (Monastir Bay, Mediterranean Sea, Tunisia). The quality of seawater as well as performance indicators such as Condition Index, length, weight, growth and frequency distribution of the mussel were determined over an annual cycle; from July 2017 to August 2018. Interestingly, P. perna has an extended sexual cycle during the year with two main spawning periods, the first in spring and the second in autumn, when suspended matter and Chlorophyll a were at their maximum concentrations in seawater. Spat mussels and young mussels showed significant growth rates from 1 July 2017 to 31 October 2017. Adult mussels exhibited negative allometric growth and a modal size of 41 to 50 mm. Results showed that several potentially toxic microalgae species developed at low densities in this marine zone. By using Solid Phase Adsorption Toxins Tracker (SPATT); lipophilic toxins including Okadaic acid and yessotoxins were detected at low levels in seawater and may be involved in the positive LSTs (lipophilic shellfish toxins) mouse bioassays in P. perna during the autumn. No other toxins such as paralytic shellfish toxins or amnesic shellfish toxins nor pathogenic bacteria or viruses were detected in P. perna. Altogether, our results suggest that finfish farms in Monastir Bay could be suitable sites for farming P. perna.

Short‐term effects on Unionid mussel density and distribution before and after low‐head dam removal in northern New York

AbstractUnionid mussel populations have declined in many environments, particularly those that were altered by human activities such as dam construction and removal. The Fort Covington Dam blocked the Salmon River in northern New York upriver of its confluence with a smaller tributary, the Little Salmon River. This dam was removed in 2009. My study compared the mean ranked density of mussels in both rivers for the pre‐removal period (2005–2008) to the post‐removal period (2009–2012) with special attention to Lampsilis cariosa and Margaritifera margaritifera. Systematic sampling was used at six riffles and double sampling at four glides divided between the Salmon and Little Salmon rivers from 2005 through 2012. The Little Salmon River served as a control. Mean ranked adult mussel density was not significantly different between the two rivers in the pre‐removal period but was significantly greater in the Little Salmon River after dam removal. Living mussels of 13 species were collected dominated by Elliptio complanata. Dam removal did not affect sediment sorting, porosity, water chemistry, or mussel species distribution. Rapid dewatering of the reservoir led to stranding and death of mussels in the reservoir and in the adjacent ponds. Increased water velocity, exacerbated by rain, mobilized sediment that buried a potentially large mussel bed downstream of the dam where Lampsilis cardium and L. cariosa were abundant, which showed little recovery by 2013.

Bottlenecks and barriers: Patterns of abundance in early mussel life stages reveal a potential obstacle to reef recovery

Abstract Conservation and restoration projects have emerged globally to address extensive declines in mussel reefs and the ecosystem services they provide. The success of these efforts relies on the re‐establishment of self‐sustaining populations, which requires mussels to effectively undergo every stage in their complex development cycle from larvae to adult mussels. In particular, the settlement of early life stages presents a potential bottleneck for recruitment in species like the green‐lipped mussel (Perna canaliculus) that rely on juvenile settlement onto macroalgae before they transition to a reef. However, it is largely unknown whether mussels can undergo settlement in areas after overharvesting where only remnant populations remain and natural recovery is vital. In this study, wild and transplanted macroalgae were sampled in an area with historically near‐extirpated mussel reefs (Kenepuru Sound, New Zealand) to examine the patterns of abundance of plantigrades, an early mussel life stage, in a degraded environment. The results suggest that plantigrades can settle to and survive on natural substrates following the removal of mussel reefs, but not into ecologically relevant areas. Specifically, almost no plantigrades were recorded on substrates near the sea bed, the area where almost all settlement to macroalgae would naturally occur. Instead, plantigrades were primarily recorded on macroalgae on docks suspended above the sea bed. A transplantation experiment verified this trend, demonstrating that substrates transferred to surface waters recorded a 36‐fold increase in plantigrade abundance compared with substrates near the sea bed. Turbidity was significantly higher near the sea bed than near the water surface, suggesting that high turbidity following the loss of wild mussels may be hindering natural plantigrade settlement or survival. This study identifies a potential bottleneck to natural mussel recovery and demonstrates the importance of a life cycle‐informed approach to restoration that prioritizes the removal of bottlenecks at multiple life stages.

Integrated Assessment of CO2-Induced Acidification Lethal and Sub-Lethal Effects on Tropical Mussels Perna perna

Leakages of CO2 capture and storage systems from the seabed are able to cause significant adverse biological effects in marine species. Adult mussels were exposed to different CO2 enrichment scenarios (pH from 8.3 to 6.0) for 96 h, and endpoints (lysosomal membrane deterioration, lipid peroxidation and primary damages in DNA) were assessed. Mortality and reduced health status can occur after short exposure of the tropical mussel Perna perna to pH levels lower than 7.5. Results pointed out cytogenotoxic effects in the hemolymph and gills after 48 and 96 h of exposure, respectively. These findings should be considered when environmental monitoring approaches are performed in tropical marine areas employing CCS strategies.

Provision of early mussel life stages via macroalgae enhances recruitment and uncovers a novel restoration technique

Mussel reefs have been decimated globally as a result of overharvesting, climate change, invasive species, and disease leading to the proliferation of conservation and restoration initiatives. Achieving and maintaining high recruitment rates is vital to the success of these efforts. Without adequate recruitment degraded areas cannot recover and reefs restored through mussel transplantation will dwindle and eventually disappear. Efforts to enhance recruitment for restoration projects typically prioritize the provision of conspecifics to attract juveniles, relying on the concept that transplanting adult mussels into a degraded environment will improve recruitment. However, the mussel aquaculture industry often pursues a different path to facilitate recruitment to their mussel farms, specifically the provision of wild-caught or hatchery-reared settlement-stage mussels (plantigrades) with the understanding that these plantigrades will then recruit onto substrates in the mussel farm. This technique has clear potential for mussel restoration practitioners seeking to enhance recruitment to a degraded area, however, it is largely untrialled in this context. In this study, a fully-factorial small-scale experiment was conducted to test the provision of adult mussels and plantigrades as techniques to enhance juvenile mussel (Perna canaliculus and Mytilus galloprovincialis) recruitment and growth in Kenepuru Sound, New Zealand, an area with a history of wild mussel overharvesting. After two-months, the provision of plantigrades via settlement-dense macroalgae resulted in a 10-fold increase in recruitment compared to the provision of adult mussels alone, as well as an increase in average juvenile recruit size. Notably, the provision of adult mussels did not enhance overall juvenile recruitment rates, however it did alter recruitment patterns as juveniles preferentially recruited directly onto conspecific adult mussels rather than rocks when provided with both options of substrate in close proximity. These results emphasize the value of healthy macroalgae populations to mussel reef functioning and shed light on a potential bottleneck to recruitment as both macroalgae populations and mussel recruitment rates have declined locally. Ultimately this study highlights the possibility of plantigrade-provision through macroalgae as an efficient recruitment enhancement technique for mussel restoration and emphasizes the importance of both cross-species and life cycle informed restoration.

First isolation of Francisella halioticida strains from blue mussel (Mytilus edulis) in Normandy, France

Mass mortality events affecting the blue mussels Mytilus edulis have been observed in France since 2014. The DNA of the bacterium Francisella halioticida, reported as pathogen of giant abalone (Haliotis gigantea) and Yesso scallop (Mizuhopecten yessoensis) has been detected recently in mussels from areas suffering mortalities. Isolation of this bacterium was attempted from individuals collected during mortality events. Identification was performed by 16S rRNA gene sequencing, real-time specific PCR and MALDI-ToF using spectra produced from the strain 8472-13A isolated from diseased Yesso scallop in Canada. Five isolates were identified as F. halioticida by real-time specific PCR and 16S rRNA sequencing. MALDI-ToF allowed the direct identification of four isolates (FR22a,b,c,d) which had 100% identity on the 16S rRNA gene with the known strains. On the other hand, one isolate (FR21) was not recognized by MALDI-ToF and had 99.9% identity on the 16S rRNA gene. The FR22 isolates showed difficult growth and required media optimization, which was not the case with the FR21 isolate. For these reasons, it was hypothesized that two type strains are present on French coasts, named FR21 and FR22. The FR21 isolate was selected for phenotypic analysis (growth curve, biochemical characteristics, electron microscopy), phylogenetic analysis and an experimental challenge. This isolate showed distinct differences compared to published F. halioticida strains, both at phenotypic and genotypic levels. Experimental infections of adult mussels led to 36% mortalities in 23 days following intramuscular injection with 3 × 107 CFU while a lower dose (3 × 103 CFU) did not lead to significant mortalities. In the context of this study, the strain FR21 was not virulent towards adult mussels.

Salinity and pH effects on survival, growth, and reproduction of quagga mussels.

In recent decades, invasive quagga mussels have expanded to the Western United States from the Great Lakes region of North America. Most studies that evaluate the invasion potential of quagga mussels in western water bodies have utilized physiological and life history information from zebra mussels, a related taxon. Few studies have assessed the potential for invasion using specific information from quagga mussel life history or experiments that test for their survival in the fresh and saline waters of the western United States. We investigated quagga mussel survival, growth, and reproduction using semi-natural experiments under temperature and light controlled conditions across a gradient of water salinity (fresh to brackish) and pH (8.4-11). Water from Lake Mead was used as a positive control in our experiment, and water from Pyramid Lake and the Truckee River was used as brackish and freshwater treatments, respectively. The mussels used in the experiments were collected from Lake Mead. After 12 h in brackish water (4 ppt, pH 9.3), we observed 100% mortality of adult mussels. The swelling and disintegration of body tissues and high mortality rates indicated that high potassium, sodium, and chloride concentrations were the likely causes of death in brackish water treatments. In contrast, mussels were able to survive, grow, and reach sexual maturity in freshwater (0.1 ppt) with a low calcium concentration (17 mg L-1) after 57 days. Mussels died after 2 days at pH 11 and after 12 days at pH 10; during the 14-day monitoring period, no mortality was detected at pH 9.0, 9.3, or 9.5 and mussels did not exhibit any visual indications of stress. Understanding quagga mussel physiological and environmental tolerances appears to be essential for assessing their invasion potential in aquatic habitats.

Modeling integrated biomarker response (IBR) index for the mussel Mytilus galloprovincialis (Lamark 1819) exposed to heavy metal mixture using the CCF design

Marine pollutants such as heavy metals (HMs) are considered among the most copious oxidative stress (OS) inducers in marine organisms which leads to reactive oxygen species (ROS) formation. Complementary to our previous bioassays studies, the present research focuses on Catalase (CAT), Glutathione S-transferase (GST) and Malondialdehyde (MDA) as oxidative stress biomarkers and the integrated biomarker response (IBR) indexes (IBR1 and IBR2) as an ecotoxicological assessment tool in Mytilus galloprovincialis using central composite face centered (CCF) design. The oxidative stress biomarkers were measured in adult mussels (45-55 mm) on 3 days-exposed under different sub-lethal concentrations of cadmium (Cd), zinc (Zn), and copper (Cu). Using multiple regressions, ANOVA analysis revealed that experimental data fitted to second-order (quadratic) polynomial equations. The results showed that types, concentrations and metals combinations has a direct effect in CAT and GST activities, MDA level and IBR indexes. Additionally, metal-metal interactions were found synergistic (supra-additive), antagonistic (infra-additive) or zero interaction in the toxicological effect. As necessary, the optimization of the experimental results was done in order to determine the optimal conditions for the oxidative stress responses and IBR indexes. It was demonstrated that the CCF design combined with the multi-biomarker approach and IBR index can be used as an appropriate tool in ecotoxicological modulation and prediction of oxidative stress and antioxidant status by heavy metals in the mussels Mytilus galloprovincialis.

Spatiotemporal bioavailability of PCDD/Fs and dl-PCBs in wild mussels from the Portuguese Atlantic coast

This study aimed to assess the spatiotemporal bioavailability of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and dioxin-like polychlorinated biphenyls (dl-PCBs) in wild adult mussels, Mytilus galloprovincialis, collected along the Portuguese Atlantic coast between 2009 and 2020. The work is part of a national environmental monitoring program. The purpose was to evaluate the dioxins’ temporal trends, the human and ecological risks, and the correlation between mussels’ location and the main pollutant sources in Portugal. The levels and congener patterns of the most toxicity-relevant 17 PCDD/Fs and 12 dl-PCBs were determined, with the dl-PCBs dominant. The sum of Σ17PCDD/Fs and Σ12dl-PCBs values ranged from 2.0 to 4.0 ng WHO-TEQ kg−1, (wet weight basis), below the limits established by the European Commission for contamination in fish and fishery products (6.5 ng per kg−1). The study included five years – 2009, 2010, 2016, 2018 and 2020 –, allowing to verify the impact of European Directive 2013/39/UE against the pollution of water in Portugal; it was observed that dioxin levels in mussels diminished over the time. Statistical analysis allowed verification of different spatial trends of dl-PCB profiles along the Portuguese Atlantic coast. The mono-ortho dl-PCB pentachlorinated congener IUPAC #118 prevailed in 2009 and 2018 in all sampling sites, and it was predominant in 2010, 2016 and 2020, followed by the congeners IUPAC #105, #156 and #167. The IUPAC #167, #169 and #123 were the most abundant hexachlorinated congeners, and the IUPAC #77 the most abundant tetrachlorinated congener. This work emphasises the importance of monitoring dioxins and mapping the congeners in Atlantic coastal ecosystems, to contribute to their elimination.

The effects of physical disturbance and sediment refuge on the growth of young native freshwater mussels Elliptio complanata (Eastern Elliptio)

Native freshwater mussels form a critical component of benthic foodwebs, but are endangered worldwide, making their study an important conservation issue. Many unionids live in shallow environments where they are potentially vulnerable to natural disturbances, but the impact of physical forces on their growth and the role of sediments as a refuge is poorly understood. Here, we validate the use of two types of shell internal lines (nacreous, prismatic) as indicators of physical disturbance and shell coloration as an indicator of sedimentary habitat. We use these indicators to test (1) whether the sediments provide an effective refuge for juvenile and young adult mussels from natural disturbances and (2) whether disturbance events affect their growth. Elliptio complanata (Eastern Elliptio) emerge from the sediments when they are 20–50 mm in size and 2.5–7 years old. Juvenile and young adults lay down more disturbance lines at more exposed nearshore sites, but also in small lake basins with dense mussel populations. Disturbance lines are produced during both endo- and epibenthic growth periods, but in contrast to adults, they are not associated with growth anomalies. Sediments accumulating in shallow nearshore areas of lakes provide an imperfect but effective refuge for native mussels that warrant protection.