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The present study is devoted to a comparison of the structure and quantitative ratio of heterogeneous spermatozoa of native wild mussels Mytilus trossulus Gould, 1850, collected in four areas of the Peter the Great Bay of the Sea of Japan (the northwestern part of the Pacific Ocean). The mussels were identified as M. trossulus by shell appearance, and the species was confirmed by sequencing the mitochondrial cytochrome c oxidase subunit I gene (COI). Heteromorphic spermatozoa were found; namely, a total of eight morphs (SPERM1–SPERM8) in M. trossulus. Surprisingly, some of the detected sperm morphs overlap morphologically with the sperms of other mytilids such as M. edulis, Crenomytilus (M.) grayanus and M. coruscus. Possible reasons for this phenomenon are discussed. In each geographic area, the 'quantitative proportions of heterogeneous spermatozoa' (QPHS) were unique. It has been suggested that the QPHS score can be considered in the context of its applicability as a biological marker for finding optimal mussel rearing sites. [ABSTRACT FROM AUTHOR]

A comparative assessment of the contents of Fe, Zn, Cu, Cd, Mn, Pb, and Ni in the soft tissues of bivalve mollusks Mytilus trossulus, Mytilus galloprovincialis, and their hybrid forms from Minonosok Bay of Peter the Great Bay (Sea of Japan) has been made. No significant differences in the accumulation of Fe and Cd in the tissues of all studied groups of mollusks were found. It has been shown that the hybrid forms of these species had more intensive growth, and against this background they accumulated significantly lower concentrations of such metals as Cu, Mn, Pb, and Ni in their soft tissues compared to the parental species. A significant negative correlation has been found between the accumulation of these metals in the tissues of mollusks and the length and weight of their shells and whole soft tissues M. trossulus, which had a significantly lower weight of valves and soft tissues, differed from M. galloprovincialis in the accumulation of significantly higher concentrations of Zn, for which no relationship has been found between its content and all the studied size and weight characteristics. The conducted testing did not reveal any significant dependence of the accumulation of all studied metals, with the exception of Pb, in the tissues of mollusks on their condition index. The results we obtained indicate the need to take the above features of the trace metal composition of the soft tissues of the studied species into account when using them in monitoring environmental pollution with heavy metals. [ABSTRACT FROM AUTHOR]

Subarctic populations of “cryptic” blue mussel species Mytilus edulis (ME) and M. trossulus (MT) are less studied than Arctic and boreal populations. Ecological features of ME and MT in sympatry are poorly known everywhere. We studied the habitat segregation of ME and MT and the interannual dynamics of their mixed settlements at the Murman coast of the Barents Sea, the northeastern boundary of the Atlantic littoral mussel communities. Previous data on mussels from this area are 50-100 years old. The 3-km-long Tyuva Inlet (Kola Bay) was used as the study site. Mussels were found in the littoral and the sublittoral down to a depth of 4 m. Their characteristic habitats were sandbanks, littoral rocks, sublittoral kelp forests and “the habitat of the mussel bed” in the freshened top of the inlet. The main spatial gradients explaining the variability of demographics of the settlements (abundance, age structure, size) were associated with the depth and the distance from the inlet top. ME and MT were partially segregated by depth: ME dominated in the sublittoral and MT, in the littoral. In addition, ME dominated throughout the mussel bed. The ratio of species in the mixed settlements varied over time: between 2004 and 2010 the proportions of MT decreased everywhere, by 22% on average. The habitat distribution of mussels apparently changed with time: we found that mussels were abundant in kelp forests, where they had rarely been observed in the 20th century. We suggest that the spatial and temporal dynamics of subarctic mussels can be partly explained by the competition between ME and MT and their differing sensitivity to environmental factors.

The pollution of coastal water areas by heavy metals is constantly growing; therefore, the study of the mechanisms of impact of these toxicants on the organisms of hydrobionts is a topical direction of toxicology. Particularly pertinent are questions about the state of the reparation system in the aquatic organisms, which make it possible to assess the resistance, survival of hydrobionts, and the probability of remote consequences under the impact of heavy metals. Therefore, in this work, we investigated genome integrity and DNA repair ability in the gill cells of Mytilus trossulus, under conditions of copper (Cu2+) accumulation, and in the process of tissue depuration from this metal. Although the biochemical detoxification system was functioning, it is noted that destructive processes developed, including the accumulation of lipid peroxidation products (MDA) and DNA damage. It was also found that in all of the experimental groups of Mytilus trossulus, in the process of depuration from Cu2+ for 24 h, the levels of DNA damage and MDA content were markedly reduced, and further reduction was less intense. [ABSTRACT FROM AUTHOR]

Mussels occupy a key middle trophic position in nearshore food webs linking primary producers to predators. Climate‐related environmental changes may synergistically combine with changes in predator abundance to affect intertidal ecosystems. We examined the influence of two major events on mussel (Mytilus trossulus) abundance in the northern Gulf of Alaska: the recent Pacific marine heatwave (PMH, 2014–2016) and an outbreak of sea star wasting (SSW). We investigated how mussel abundance changed since the onset of SSW and whether the density of predatory sea stars or PMH‐related temperature metrics explain variation in mussel abundance. Sea stars and mussels were surveyed since 2005 approximately annually in four regions of the northern Gulf of Alaska: Katmai (KATM), Kachemak Bay (KBAY), Kenai Fjords (KEFJ) and western Prince William Sound (WPWS). Mussel percent cover in the mid‐intertidal increased 1–3 years after declines in sea stars at all regions and in the low‐intertidal at KATM, KBAY, and KEFJ, but not at WPWS. After the onset of SSW, large (≥20 mm length) mussel density and mussel bed width increased at KATM but not the other regions. Total mussel densities, including recruits, did not differ before and after the onset of SSW. The total number of sea stars significantly explained variation in mussel metrics, but the proportions of the three sea star species examined did not. We did not find strong evidence for direct effects of temperature on mussels. The effects of the PMH and the SSW outbreak appear to have combined, with increased temperatures indirectly benefiting mussels in concert with relaxed top‐down pressure from sea stars, allowing for increased mussel abundance. Changing mussel abundance may affect intertidal local productivity and the abundance or performance of other nearshore consumers of mussels. [ABSTRACT FROM AUTHOR]

Bivalves frequently withstand shell damage that must be quickly repaired to ensure survival. While the processes that underlie larval shell development have been extensively studied within the context of ocean acidification (OA), it remains unclear whether shell repair is impacted by elevated pCO2. To better understand the stereotypical shell repair process, we monitored mussels (Mytilus edulis) with sublethal shell damage that breached the mantle cavity within both field and laboratory conditions to characterize the deposition rate, composition, and integrity of repaired shell. Results were then compared with a laboratory experiment wherein mussels (Mytilus trossulus) repaired shell damage in one of seven pCO2 treatments (400–2500 µatm). Shell repair proceeded through distinct stages; an organic membrane first covered the damaged area (days 1–15), followed by the deposition of calcite crystals (days 22–43) and aragonite tablets (days 51–69). OA did not impact the ability of mussels to close drill holes, nor the microstructure, composition, or integrity of end-point repaired shell after 10 weeks, as measured by µCT and SEM imaging, energy-dispersive X-ray (EDX) analysis, and mechanical testing. However, significant interactions between pCO2, the length of exposure to treatment conditions, the strength and inorganic content of shell, and the physiological condition of mussels within OA treatments were observed. These results suggest that while OA does not prevent adult mussels from repairing or mineralizing shell, both OA and shell damage may elicit stress responses that impose energetic constraints on mussel physiology. [ABSTRACT FROM AUTHOR]

In the commercial Pacific mussel species, Mytilus trossulus, from the Sea of Japan, features of the morphological structure of the byssal apparatus, byssal threads, and pedal groove are studied. Steps in the process of byssal threads formation and characters of the morphological structure of the byssal groove related to this process are described in M. trossulus. The byssal apparatus is shown to consist of a root, a stem, and byssal threads, the latter in cross section being ellipsoid in shape. A byssal thread consists of a corrugated proximal part located immediately behind the cuff and is one-third of its length, and a relatively smooth and flexible distal part taking up two-thirds of the thread length and ending with an attachment disk at the distal end. On the surface of the attachment disk, three reinforcing cords are situated. The morphological features observed in these structures are discussed in terms of the spatial distribution of mytilids in marine coastal zones, a successful habitat of M. trossulus being rocky shores with active wave activities. [ABSTRACT FROM AUTHOR]

The crystallographic texture of modern, subfossil and fossils (Upper Pleistocene) shells of the bivalves Mytilus galloprovincialis, modern and subfossil Mytilus trossulus, as well as modern and fossil (Upper Pleistocene) Ostrea edulis are studied using neutron diffraction. It is revealed that shells of mussel species of different ages are characterized by a high ordering of calcite crystals—a sharp texture. Aragonite crystals are poorly distributed, depending on the shape of the valves. In a warm, dry climate, shells of M. galloprovincialis undergo stratification of the shell matter, which violates the crystallographic texture. Under land conditions, the ordering of calcite crystals in M. galloprovincialis shells decreases. In the subfossil M. trossulus and fossil M. galloprovincialis and O. edulis, the crystallographic texture intensity of the calcite and aragonite changes over hundreds and thousands of years. [ABSTRACT FROM AUTHOR]

The potential productivity of oysters and mussels was estimated for Voevoda Bay (Russky Island, Primorskii krai) using the FARM model. The main sources of primary production in the study area are seagrass (Zostera marina) and phytoplankton (diatoms). The area of Zostera growth was delineated based on the bottom survey of the bay. The parameters of organic matter production of Zostera and phytoplankton for each computational grid cell were modeled using the ECO BLOOM II Algae module, which is part of the DELWAQ model of the Delft3D software package. Spatial redistribution of organic matter, chlorophyll a and phytoplankton were simulated using the results of hydrodynamic modelling of the DELFT3D Flow. The values of biological (primary production) and hydrochemical (temperature, salinity, oxygen content) parameters, obtained for each computational grid cell were used as input to the FARM. The empirical exceedance probability curves of modelled productivity for pasture and cage cultivation of the giant oyster (Crassostrea gigas) and the Pacific mussel (Mytilus trossulus) were calculated for each cell. The spatial distribution for the potential productivity values of the representative exceedance probability (50, 75, and 95%) for both types of cultivation was mapped. [ABSTRACT FROM AUTHOR]

Baltic blue mussels can colonise and dominate habitats with far lower salinity (

The pollution of coastal water areas by heavy metals is constantly growing; therefore, the study of the mechanisms of impact of these toxicants on the organisms of hydrobionts is a topical direction of toxicology. Particularly pertinent are questions about the state of the reparation system in the aquatic organisms, which make it possible to assess the resistance, survival of hydrobionts, and the probability of remote consequences under the impact of heavy metals. Therefore, in this work, we investigated genome integrity and DNA repair ability in the gill cells of Mytilus trossulus, under conditions of copper (Cu2+) accumulation, and in the process of tissue depuration from this metal. Although the biochemical detoxification system was functioning, it is noted that destructive processes developed, including the accumulation of lipid peroxidation products (MDA) and DNA damage. It was also found that in all of the experimental groups of Mytilus trossulus, in the process of depuration from Cu2+ for 24 h, the levels of DNA damage and MDA content were markedly reduced, and further reduction was less intense.

The biomechanics of specialized mechanical structures produced by organisms provides crucial fitness advantages. The energetic cost associated with producing these structural materials and the resulting energetic trade‐off with growth, however, is rarely quantified. We integrate resource allocation to structural material production with an energetic framework by combining an experimental manipulation with an energetic model.Mytilid bivalves produce byssus, a network of collagen‐like threads that tethers individuals to hard substrate. We hypothesized that a manipulation that induces the production of more byssal threads would result in increased energetic cost and decreased growth of the species Mytilus trossulus.In month‐long field experiments in spring and autumn, we severed byssal threads across a range of frequencies (never, weekly, daily), and measured shell and tissue growth. We then quantified the costs associated with the production of byssal threads using a Scope for Growth model.We found that byssal thread removal increased byssal thread production and decreased growth. The cost calculated per byssal thread was similar in the spring and autumn (~1 J/thread), but energy budget calculations differed by season, and depended on thread quantity and seasonal differences in assumptions of metabolic costs.This work demonstrates that the cost of producing a structural material has a substantial effect on mussel energetic state. The energetic cost of producing byssal threads was 2%–8% percent of the energy budget in control groups that had low byssal thread production, and increased six to 11‐fold (up to 47%) in mussels induced to produce threads daily.We propose that characterizing the trade‐off between the cost of biomaterial production and growth has implications for understanding the role of trade‐offs in adaptive evolution, and improved natural resource management and conservation practices. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

The possibility of using a battery of biomarkers, that is, the lysosomal membrane stability (LMS), the genetic damage index (GDI), the activities of catalase (CAT) and glutathione-S-transferase (GSТ), the level of malondialdehyde (MDA), and the condition index (CI), was tested for the assessment of pollution in the marine environment. These characters were used to calculate an index reflecting the integrated biomarker response (IBR). The obtained index confirmed the known degree of marine pollution, which increases in the series Vostok Bay < Kozmina Bay < Golden Horn Bay. [ABSTRACT FROM AUTHOR]

Understanding and predicting responses of ectothermic animals to temperature are essential for decision-making and management. The thermal performance curve (TPC), which quantifies the thermal sensitivity of traits such as metabolism, growth and feeding rates in laboratory conditions, is often used to predict responses of wild populations. However, central assumptions of this approach are that TPCs are relatively static between populations and that curves measured under stable temperature conditions can predict performance under variable conditions. We test these assumptions using two latitudinally matched populations of the ecosystem engineer Mytilus trossulus that differ in their experienced temperature variability regime. We acclimated each population in a range of constant or fluctuating temperatures for six weeks and measured a series of both short term (feeding rate, byssal thread production) and long-term (growth, survival) metrics to test the hypothesis that performance in fluctuating temperatures can be predicted from constant temperatures. We find that this was not true for any metric, and that there were important interactions with the population of origin. Our results emphasize that responses to fluctuating conditions are still poorly understood and suggest caution must be taken in the use of TPCs generated under constant temperature conditions for the prediction of wild population responses. [ABSTRACT FROM AUTHOR]

Two lineages of bivalve transmissible neoplasia (BTN), BTN1 and BTN2, are known in blue mussels Mytilus. Both lineages derive from the Pacific mussel M. trossulus and are identified primarily by their unique genotypes of the nuclear gene EF1α. BTN1 is found in populations of M. trossulus from the Northeast Pacific, while BTN2 has been detected in populations of other Mytilus species worldwide but not in M. trossulus itself. Here we examined M. trossulus from the Sea of Japan (Northwest Pacific) for the presence of BTN. Using hemocytology and flow cytometry of the hemolymph, we confirmed the presence of disseminated neoplasia in our specimens. Cancerous mussels possessed the BTN2 EF1α genotype and two mitochondrial haplotypes with different recombinant control regions, similar to that of common BTN2 lineages. This is the first report of BTN2 in its original host species M. trossulus. A comparison of all available BTN and M. trossulus COI sequences suggests a common and recent origin of BTN2 diversity in populations of M. trossulus outside the Northeast Pacific, possibly in the Northwest Pacific. [ABSTRACT FROM AUTHOR]

Bivalves frequently withstand shell damage that must be quickly repaired to ensure survival. While the processes that underlie larval shell development have been extensively studied within the context of ocean acidification (OA), it remains unclear whether shell repair is impacted by elevated pCO2. To better understand the stereotypical shell repair process, we monitored mussels (Mytilus edulis) with sublethal shell damage that breached the mantle cavity within both field and laboratory conditions to characterize the deposition rate, composition, and integrity of repaired shell. Results were then compared with a laboratory experiment wherein mussels (Mytilus trossulus) repaired shell damage in one of seven pCO2 treatments (400–2500 µatm). Shell repair proceeded through distinct stages; an organic membrane first covered the damaged area (days 1–15), followed by the deposition of calcite crystals (days 22–43) and aragonite tablets (days 51–69). OA did not impact the ability of mussels to close drill holes, nor the microstructure, composition, or integrity of end-point repaired shell after 10 weeks, as measured by µCT and SEM imaging, energy-dispersive X-ray (EDX) analysis, and mechanical testing. However, significant interactions between pCO2, the length of exposure to treatment conditions, the strength and inorganic content of shell, and the physiological condition of mussels within OA treatments were observed. These results suggest that while OA does not prevent adult mussels from repairing or mineralizing shell, both OA and shell damage may elicit stress responses that impose energetic constraints on mussel physiology.

Microplastic pollution of the aquatic environment is one of the most serious environmental problems today. The potential environmental risks of such particles have become growing concerns in recent years, as direct or indirect exposure to these particles leads to adverse effects on marine organisms. In this study, we investigated the potential risk of polystyrene (PS) microspheres on the genome integrity of cells of different tissues (gills and digestive gland) of the filter-feeder mollusk Mytilus trossulus, using a comet assay. With the help of the comet assay, we estimated the level of genome destruction in the cells of two different mussel tissues after short-term exposure to polystyrene. It was discovered that, despite their chemical inertness, PS microspheres that are 0.9 µm in diameter, at a concentration of 106 particles/L, exhibit genotoxic properties, which are expressed as a two-fold increase in the level of cell DNA damage of the mussel’s digestive gland. It is noted that, after exposure to PS, about half of the mussel’s digestive gland cells experienced damage in 25–35% of their DNA. In addition, the proportion of cells with significant DNA damage (50%) was about 5%. Given the unique role of the genome, DNA damage in these cells may be the earliest stage in the development of biochemical events that lead to toxic effects. These findings provide a basis for studying specific biomarkers of microplastic contamination.

Mussel beds are common in many intertidal and subtidal habitats, including sub-Arctic and Arctic regions. Despite their ecological importance, little is known about the demographic processes governing the development of mussel beds and particularly about the synchronization of these processes at different spatial scales. The development of a relatively compact, narrow littoral mussel bed of Mytilus trossulus, extending several hundred m along the shore of Koni Peninsula (Tauyskaya Bay, northern Sea of Okhotsk), was studied for four years during the period 2014–2017. This model bed was located along an exposed coast with a seasonal sea ice cover. It was used to test the hypothesis that small-scale synchronization exists, i.e., the changes in demographic structure of the population that occur simultaneously within a single mussel bed follow a similar pattern. This hypothesis was rejected. The size structure of the mussel population at the same tidal level changed from being uniform (2014) to being varied in 2015–2017. The course of development of the mussel population was different at the opposite ends of the bed. The cause of these differences may be unequal levels of recruitment of juveniles in the form of a gradient from one end of the bed to the other over the length of the bed. The gradient was associated with transition from one type of shore dynamic processes to another (accumulation vs. abrasion). Small-scale desynchronization may represent one of the reasons explaining the heterogeneity of mussel populations. The possibility of desynchronization of demographic processes should be taken into consideration when studying the spatial organization and dynamics of mussel beds. [ABSTRACT FROM AUTHOR]

Invasive aquatic species can pose serious ecological and economic threats to coastal habitats. Although the mechanisms by which invasive species are introduced are generally well understood, and frequently caused by discharging ballast water, less is known about the physiological characterists that allow an invasive species to proliferate so successfully.

Coastal regions worldwide face increasing management concerns due to natural and anthropogenic forces that have the potential to significantly degrade nearshore marine resources. The goal of our study was to develop and test a monitoring strategy for nearshore marine ecosystems in remote areas that are not readily accessible for sampling. Mussel species have been used extensively to assess ecosystem vulnerability to multiple, interacting stressors. We sampled bay mussels (Mytilus trossulus) in 2015 and 2016 from six intertidal sites in Lake Clark and Katmai National Parks and Preserves, in south-central Alaska. Reference ranges for physiological assays and gene transcription were determined for use in future assessment efforts. Both techniques identified differences among sites, suggesting influences of both large-scale and local environmental factors and underscoring the value of this combined approach to ecosystem health monitoring.

Coastal regions worldwide face increasing management concerns due to natural and anthropogenic forces that have the potential to significantly degrade nearshore marine resources. The goal of our study was to develop and test a monitoring strategy for nearshore marine ecosystems in remote areas that are not readily accessible for sampling. Mussel species have been used extensively to assess ecosystem vulnerability to multiple, interacting stressors. We sampled bay mussels (Mytilus trossulus) in 2015 and 2016 from six intertidal sites in Lake Clark and Katmai National Parks and Preserves, in south-central Alaska. Reference ranges for physiological assays and gene transcription were determined for use in future assessment efforts. Both techniques identified differences among sites, suggesting influences of both large-scale and local environmental factors and underscoring the value of this combined approach to ecosystem health monitoring. [ABSTRACT FROM AUTHOR]

Abstract Interest in the presence of pharmaceutically active compounds in the aquatic environment has been growing for over 20 years, yet very few studies deal with the metabolism of pharmaceuticals in marine organisms. In this study, the bioaccumulation under short-term conditions and metabolism of diclofenac were investigated. Mytilus trossulus was used as a representative of the Baltic benthic fauna. The mussels were exposed to diclofenac at a concentration of 133.33 μg/L for five days, following a five-day depuration phase. The highest concentration of diclofenac (7.79 μg/g dw) in tissues was determined on day 3. Subsequently, the concentration of diclofenac in tissues decreased rapidly to 0.86 μg/g dw on day 5. After five days of depuration, the concentration of diclofenac was 0.21 μg/g dw. Hydroxylated diclofenac metabolites were found both in tissues of mussels and water. This study shows that M. trossulus has the potential to accumulate diclofenac and metabolize it to 4-OH and 5-OH diclofenac. Highlights • Diclofenac is absorbed and accumulated in soft tissues by M. trossulus • M. trossulus metabolize diclofenac to 4-OH diclofenac and 5-OH diclofenac • Absorption and accumulation of diclofenac by M. trossulus depends on exposure time • Diclofenac undergoes partial degradation in artificial seawater [ABSTRACT FROM AUTHOR]

Changes in climate-related factors such as ice coverage, water temperature, and ocean currents have been proposed to facilitate an increased interchange of species in the High Arctic between the Pacific and Atlantic oceans. In Greenland, the colonization of the mussel species Mytilus edulis has been suggested to have occurred recently and exclusively from Northwest Atlantic populations. The source population for its sibling species Mytilus trossulus is however unknown, and therefore we aimed to explore its genetic origin. Using 54 SNP markers, M. trossulus was identified from three Greenland blue mussel populations collected in 2012–2014 and the relative similarities to Northwest Atlantic and North Pacific M. trossulus populations were assessed. Populations were found to fall into two clades. The North Pacific is the most likely source for the northern Greenland M. trossulus probably as a result of occasional postglacial long-distance dispersal through the Bering Strait. Our findings in M. trossulus are in agreements with the predictions that climate change will, in addition to driving a northward expansion of temperate-boreal species into the Arctic Ocean, increase the rate of trans-Arctic interchange between the Atlantic and the Pacific oceans. [ABSTRACT FROM AUTHOR]

Abstract The gene of mtl from the mussel Mytilus trossulus was cloned into pET-40b(+) expression vector. After expression in E. coli using designed MX-medium an instable soluble form of MTL was obtained. The developed isolation method of the recombinant protein in "semi-denatured" conditions allowed obtaining an active soluble form of the homogenous lectin from the mussel M. trossulus (r-MTL). Both of the lectins had similar antigenic and spatial structures. Highlights • The recombinant analog of Mytilus trossulus lectin, a member of new lectin family was obtained in soluble and active form. • A method of isolation of the recombinant protein in "semi-denatured" conditions was developed. • It has been shown that native MTL and recombinant MTL have similar spatial structures and biological activity. [ABSTRACT FROM AUTHOR]

Anthropogenic warming of the ocean and atmosphere, concurrent with ocean acidification and deoxygenation, has made it even more pressing to quantify the link between environmental stressors and marine organism population dynamics. In marine environments, low food availability, low feeding rates, and/or increased metabolic costs can cause energetic limitation. Energetic limitation affects some functional traits, such as growth rates of body tissue and reproductive output. Other functional traits that are linked with short-term survival are often prioritized in conditions of energy limitation, despite their energetic cost. Mussels are ecosystem engineers in rocky shore ecosystems, and they produce byssal threads to attach to hard substrate and aquaculture line. Previous studies of mytilid mussel bioenergetics suggest tissue and shell growth are energetically-constrained, while production of byssal threads presents a fitness trade-off and could potentially be a fixed or 'constitutive' response regardless of energetic state. In this study, we conduct a field test with two congener mussel species, Mytilus trossulus and Mytilus galloprovincialis to determine whether an index of energetic availability, scope for growth (SFG), correlates with growth and byssal thread production, and the extent to which other potential stressors (hypoxia, low pH, low salinity and high temperature) modulate this response. We find a positive correlation between SFG and growth (both tissue and shell) but not the number of byssal threads produced. We also find low pH or low DO, two co-varying physiological stressors, negatively affect tissue growth of both species, but only marginally affect byssal thread production. We also observed mortality in the late summer/early autumn that coincides with the period of greater hypoxia and low pH. Overall, this work suggests that some functional traits, such as shell and tissue growth, are energetically-constrained while other functional traits, such as mussel byssal thread production, may be best described as a fitness trade-off. [Display omitted] • Mussel growth and mechanical attachment (byssal thread production) evaluated in response to environmental conditions at a mussel farm. • Energetics framework was used to predict feeding rate and metabolic cost as functions of temperature. • Energetics was a significant predictor of mussel growth. • Duration of co-occurring hypoxia / low pH, prevalent at depth, was also a predictor of mussel growth. • Suggests byssal thread production is constitutive and not a 'flexible' trait across a gradient of energy limitation. [ABSTRACT FROM AUTHOR]

A GalNAc/Gal-specific lectins named CGL and MTL were isolated and characterized from the edible mussels Crenomytilus grayanus and Mytilus trossulus. Amino acid sequence analysis of these lectins showed that they, together with another lectin MytiLec-1, formed a novel lectin family, adopting β-trefoil fold. In this mini review we discuss the structure, oligomerization, and carbohydrate-binding properties of a novel lectin family. We describe also the antibacterial, antifungal, and antiproliferative activities of these lectins and report about dependence of activities on molecular properties. Summarizing, CGL, MTL, and MytiLec-1 could be involved in the immunity in mollusks and may become a basis for the elaboration of new diagnostic tools or treatments for a variety of cancers.

The ingestion of microlitter by blue mussels (450) was studied at a wastewater recipient area in the Baltic Sea. The mussel soft tissues were digested using enzymatic detergents and the detected litter particles characterized with FT-IR imaging spectroscopy. Microlitter concentration in seawater and WWTP effluent were also measured. Microlitter was found in 66% of the mussels. Mussels from the WWTP recipient had higher microlitter content compared to those collected at the reference site. Plastics made up 8% of all the analysed microlitter particles. The dominating litter types were fibres (~90% of all microlitter), 42% of which were cotton, 17% linen, 17% viscose and 4% polyester. The risk of airborne contamination during laboratory work was lowered when mussels were digested with their shells on instead of dissecting them first. The approach was found applicable and gentle to both non-synthetic and synthetic materials including fragile fibres. [ABSTRACT FROM AUTHOR]

The role of seawater NOM in reducing metal toxicity for marine organisms is not well understood. We investigated the effects of five different marine NOMs (two autochthonous, one allochthonous, two of mixed origin, at 8 mg C/L), three metals (6 μg Cu/L; 20 μg Pb/L; 25 μg Zn/L), and combinations between them, to early life stages of Mytilus trossulus (a North Pacific native) in 48-h tests. Endpoints were whole body Ca 2+ +Mg 2+ -ATPase activity, carbonic anhydrase (CA) activity and lipid peroxidation. Comparisons were made with previously reported tests (identical conditions) on the invasive M. galloprovincialis . Unexposed M. trossulus had lower Ca 2+ +Mg 2+ -ATPase but similar baseline CA activity and lipid peroxidation to unexposed M. galloprovincialis . NOMs alone induced increased enzyme activities, and increased lipid peroxidation, but the latter did not occur with NOMs of mixed origin in M. trossulus . There was no clear difference in the sensitivity to various NOMs between species. In M. trossulus , all three metals by themselves caused increases in lipid peroxidation, as did many metal-NOM combinations. The origin of the NOMs influenced the nature of the responses to NOM-metal combinations in both species, but no clear relationship to NOM chemistry was apparent. Overall, M. trossulus was more sensitive to metals and NOM-metal combinations, with a greater number of significant responses (27 versus 22 treatment endpoints, out of a total of 72) and a greater proportion of negative effects (81% versus 50%) than in M. galloprovincialis. Therefore, marine NOMs by themselves, as well as metals by themselves and NOM-metal combinations, can induce both positive and negative physiological responses. Lipid peroxidation appears to be a particularly common negative response. In future studies, NOM quality and mussel species should be considered since native M. trossulus and invasive M. galloprovincialis exhibited markedly different responses after exposure to the same environmental conditions. [ABSTRACT FROM AUTHOR]

This paper describes changes in the content of free steroid hormones e.g. testosterone (T), estradiol-17β (E2), estrone (E1) and estriol (E3) of Mytilus trossulus from the southern Baltic Sea as a function of season, stage of gametogenesis, sex, tissue (gonadal and somatic) and depth. The highest levels of T, E2, E1 and E3 were found in mussels sampled in spring and summer while the lowest levels were found in winter. This pattern was stable and was seen in both sexes and tissues in mussels from both mussel beds. The spring and summer peaks in steroid levels (SL) coincided with advanced levels of gametogenesis (the highest gonadal index, GI) of our model species. But, the lowest GI (autumn) and the lowest steroids content (winter) did not overlap. Instead, water temperature increase was followed by increase of SL and vice versa. This suggests that steroids may not be actively involved in the early stages of gamete development and does not preclude them from potentially being involved as endogenous modulators in the final stages of reproduction (e.g. spawning). Hence, observed fluctuations in SL in our model species are unlikely to be caused by reproductive cycle but are rather of unknown nature, likely linked with environmental conditions. Sex-related differences in steroid content included estrogen domination in females and androgen domination in males. A trend towards higher level of steroids in gills than in gonads was found, supporting the hypothesis about an exogenous origin of steroids in bivalves. However, based on the present results, we cannot exclude the possibility that these steroids have both an endogenous and exogenous origin. [ABSTRACT FROM AUTHOR]

Sea stars Asterias rubens are important natural enemies of the blue mussel Mytilus in the North Atlantic. We asked whether these predators distinguish between the cryptic species M. edulis and M. trossulus that occur sympatrically in the White Sea. In mixed experimental stocks, the odds of being eaten by sea stars were about four times greater for M. trossulus. We also showed that A. rubens preferred smaller mussels to larger ones, irrespective of their species affinity. Our findings support earlier indirect observations showing that sea stars recognize M. trossulus as a more preferable prey than M. edulis. Dramatic differences in the vulnerability to sea star predation may explain the segregation of habitats between the two mussel species in contact zones; M. trossulus usually tends to occupy habitats where the sea star predators are scarce. [ABSTRACT FROM AUTHOR]

Marine mussels (Mytilus trossulus) attach to a wide variety of surfaces underwater using a protein adhesive that is cured by the surrounding seawater environment. In this study, the influence of environmental post-processing on adhesion strength was investigated by aging adhesive plaques in a range of seawater pH conditions. Plaques took 8-12 days to achieve full strength at pH 8, nearly doubling in adhesion strength (+94%) and increasing the work required to dislodge (+59%). Holding plaques in low pH conditions prevented strengthening, causing the material to tear more frequently under tension. The timescale of strengthening is consistent with the conversion of DOPA to DOPA-quinone, a pH dependent process that promotes cross-linking between adhesive proteins. The precise arrangement of DOPA containing proteins away from the adhesive-substratum interface emphasizes the role that structural organization can have on function, an insight that could lead to the design of better synthetic adhesives and metal-coordinating hydrogels. [ABSTRACT FROM AUTHOR]

Abstract: A key component to understanding the evolutionary response to a changing climate is linking underlying genetic variation to phenotypic variation in stress response. Here, we use a genome‐wide association approach (GWAS) to understand the genetic architecture of calcification rates under simulated climate stress. We take advantage of the genomic gradient across the blue mussel hybrid zone (Mytilus edulis and Mytilus trossulus) in the Gulf of Maine (GOM) to link genetic variation with variance in calcification rates in response to simulated climate change. Falling calcium carbonate saturation states are predicted to negatively impact many marine organisms that build calcium carbonate shells – like blue mussels. We sampled wild mussels and measured net calcification phenotypes after exposing mussels to a ‘climate change’ common garden, where we raised temperature by 3°C, decreased pH by 0.2 units and limited food supply by filtering out planktonic particles >5 μm, compared to ambient GOM conditions in the summer. This climate change exposure greatly increased phenotypic variation in net calcification rates compared to ambient conditions. We then used regression models to link the phenotypic variation with over 170 000 single nucleotide polymorphism loci (SNPs) generated by genotype by sequencing to identify genomic locations associated with calcification phenotype, and estimate heritability and architecture of the trait. We identified at least one of potentially 2–10 genomic regions responsible for 30% of the phenotypic variation in calcification rates that are potential targets of natural selection by climate change. Our simulations suggest a power of 13.7% with our study's average effective sample size of 118 individuals and rare alleles, but a power of >90% when effective sample size is 900. [ABSTRACT FROM AUTHOR]

The 1989 Exxon Valdez oil spill damaged a wide range of natural resources, including intertidal communities, and post-spill studies demonstrated acute and chronic exposure and injury to an array of species. Standard toxicological methods to evaluate petroleum contaminants have assessed tissue burdens, with fewer assays providing indicators of health or physiology, particularly when contaminant levels are low and chronic. Marine mussels are a ubiquitous and crucial component of the nearshore environment, and new genomic technologies exist to quantify molecular responses of individual mussels to stimuli, including exposure to polycyclic aromatic hydrocarbons (PAHs). We used gene-based assays of exposure and physiological function to assess chronic oil contamination using the Pacific blue mussel, Mytilus trossulus . We developed a diagnostic gene transcription panel to investigate exposure to PAHs and other contaminants and its effects on mussel physiology and health. During 2012–2015, we analyzed mussels from five field sites in western Prince William Sound, Alaska, with varying oil histories from the 1989 Exxon Valdez oil spill, and from three boat harbors in the area. Gene transcription patterns of mussels from harbors were consistent with elevated exposure to PAHs or other contaminants, whereas transcription patterns of mussels sampled from shorelines in areas affected by the oil spill indicated no PAH exposure. [ABSTRACT FROM AUTHOR]

This study described the occurrence of abnormalities in bivalve larvae from the Puck Bay. Analyses of plankton samples collected in 2012–2013 showed that larval Mytilus trossulus , Mya arenaria , and Cerastoderma glaucum exhibited abnormalities that could indicate adverse environmental impacts. The deformities were mainly in shells, but missing soft tissue fragments and protruding vela were also noted. In addition to larval studies, we analyzed benthic postlarvae of Mytilus trossulus . Interestingly, grooves and notches at different locations of the prodissoconch, dissoconch, and shell margin were observed. Some of these deformations were reminiscent of the indentations found on the shell edge of larvae. Comparing the proportion of abnormal postlarvae to larvae with shell abnormalities suggested that the survival of larvae with shell abnormalities was low. Overall, our results suggested that the ratio of abnormal bivalve larvae could be used as an indicator of the biological effects of hazardous substances in the pelagic environment. [ABSTRACT FROM AUTHOR]

Protein–protein interactions play a central role in the gamete attraction, binding, and fusion stages of gamete interactions and fertilization for broadcast spawning species, such as marine mussels in theMytilus edulisspecies complex. Although assortative gamete interaction has been implicated in the level of reproductive isolation among the three species in this complex, the molecular basis of these interactions has not been elucidated. Using mass spectrometry peptide sequencing, cDNA sequencing, and bioinformatics approaches, we have investigated species-level variation in the proteins expressed on the surface of mussel eggs. We herein describe an extracellular protein, MESP-1, from the surface of the eggs ofM. edulisandM. trossulusthat has a unique domain structure when compared to protein structures that have heretofore been identified. Given variation in the size of MESP-1 predicted from cDNA sequences versus those estimated from SDS-PAGE gels, we conclude this protein is subject to significant species-specific post-translation modifications. Further, bioinformatic analysis of the novel structure of MESP-1 suggests that this protein may be an integral membrane protein involved in sperm–egg fusion, and/or released to the vitelline envelope. [ABSTRACT FROM AUTHOR]

The blue mussels Mytilus galloprovincialis and M. trossulus are competing species with biogeographical ranges set in part by environmental exposure to heat and hyposalinity. The underlying cellular mechanisms influencing interspecific differences in stress tolerance are unknown, but are believed to be under regulation by sirtuins, nicotinamide adenine dinucleotide (NAD+)-dependent deacylases that play a critical role in the cellular stress response. A comparison of the proteomic responses of M. galloprovincialis and M. trossulus to an acute heat shock in the presence and absence of the sirtuin inhibitor suramin (SIRT1, 2 and 5) showed that sirtuins affected molecular chaperones, oxidative stress proteins, metabolic enzymes, cytoskeletal and signaling proteins more in the heatsensitive M. trossulus than in the heat-tolerant M. galloprovincialis. Interactions between sirtuin inhibition and changes in the abundance of proteins of β-oxidation and oxidative stress in M. trossulus suggest a greater role of sirtuins in shifting metabolism to reduce the production of reactive oxygen species near thermal limits. Furthermore, RNA-binding proteins initiating and inhibiting translation were affected by suramin in M. galloprovincialis and M. trossulus, respectively. Western blot analysis showed that the levels of mitochondrial sirtuin 5 (SIRT5) were generally three times higher and increased with acute heat stress in response to sirtuin inhibition in M. trossulus but not in M. galloprovincialis, suggesting a possible feedback response in the former species and a greater reliance on SIRT5 for its stress response. Our findings suggest that SIRT5 plays an important role in setting interspecific differences in stress tolerance in Mytilus by affecting the stress proteome. [ABSTRACT FROM AUTHOR]

In a temporal comparison over 18 years, we documented changes in the position and structure of the North European blue mussel hybrid zone in the Öresund strait, between Mytilus edulis of the marine Kattegat and Mytilus trossulus of the brackish Baltic Sea. In 1987 the midpoint of the 140-km wide multilocus allozyme cline in shallow-water populations was estimated to be located half-way along the strait. In 2005, it was shifted 25 km towards the Baltic end of the Öresund, and was located near the fixed link (bridge) that was built across the strait meanwhile in the 1990s. The cline also appeared to have become narrower and the extent of hybridity among individuals decreased. Factors that theoretically can control the position and shape of a clinal hybrid zone involve environmental gradients between habitats that differentially favor the two hybridizing taxa, or barriers to geographical dispersal of the organism. We consider two alternative hypotheses to explain the movement of the mussel hybrid zone. (1) Environmental change related to climate warming: the more stenothermal M. trossulus was pushed out from the Öresund towards the cool Baltic by elevated temperatures. (2) Change of dispersal dynamics: the construction of the fixed link locally affected mussel dispersion which attracted the zone. We raise the question whether similar changes have taken place also in the other euryhaline taxa where genetic clines between Baltic vs. Kattegat populations occur. [ABSTRACT FROM AUTHOR]

Doubly uniparental inheritance of mitochondria (DUI) is best known in the blue mussel Mytilus. Under this model, two types of mitochondrial DNA exist: female type (F), transmitted from females to offspring of both genders, and male type (M), transmitted exclusively from males to sons. The mitogenomes are usually highly divergent, but an occasional replacement of a typical M genome by a particular F genome has been postulated to explain reduction of this divergence. Disruption of the DUI model has been reported in hybridization areas. Here, we present a new case of DUI disruption in a hybrid M. trossulus/M. edulis population from the North Sea (Norway). No M haplotypes derived from M. trossulus were identified in this population. Typical M haplotypes derived from M. edulis (ME) were rare. Two F-type haplogroups were found: one derived from M. edulis (FE) and the second derived from M. trossulus (FT). Many haplotypes from the FT group were recombinants, with the male CR sequence coming from the M. trossulus genome (FT1 haplogroup) in contrast to M. edulis CR as in the Baltic. FT1 haplotypes were abundant in the studied population, including homoplasmic females. However, males significantly more often carried these haplotypes; therefore, male heteroplasmy involved the original FE and recombinant FT, indicating that the FT genome undergoes masculinization. Structural similarity of FT1 CR with previously reported, masculinized Baltic haplotypes, which were derived from FE/ME recombination, provides further evidence that CR M-F recombination is a prerequisite for masculinization, also in the context of native M. trossulus mtDNA. [ABSTRACT FROM AUTHOR]

Ecological mussel farming in the Baltic Sea has gained attention due to ability of mussels to bind high concentrations of nitrogen and phosphorus in their tissues. Removal of mussels could serve as abatement of eutrophication. The Latvian coast of the Baltic Sea is one of the most exposed coastlines of the Baltic due to the highest wind and wave energy. Experimental units for mussel recruitment were placed in three locations at 15, 20 and 25 m depth assess the potential for mussel farming. The spawning maximum was observed in the middle of May, followed by recruitment in June. Recruitment of Mytilus was observed on all experimental units with higher densities at 6 to 10 m depth. Observations suggest that mussels can use artificial substrate for recruitment even near high energy shores. However, if mussel farming is to take place, submerged offshore farming techniques should be considered. [ABSTRACT FROM AUTHOR]

Species distribution models often assume homogeneous physiological performance within a species distribution range. This assumption potentially underestimates the distribution as it neglects physiological plasticity and adaptation among species and populations. Better knowledge on the physiological variation is, therefore, needed to better predict the effects of global warming on species distribution. Mussels in the genus Mytilus are known to display latitudinal variation in whole animal aerobic metabolism. Here we test the hypothesis that latitudinal variation in whole animal metabolic rate of two congeners of Mytilus ( Mytilus edulis collected 56°N, and Mytilus trossulus collected 77°N) is related to differences in mitochondrial respiration. We further investigated the changes in mitochondrial respiration following long-term cold-water acclimation of M. edulis. We assessed mitochondrial respiration after five months of acclimation to 1 and 15 °C. At similar experimental temperatures, mitochondrial respiration in animals acclimated to 1 °C was higher compared to those acclimated to 15 °C. After five months of acclimation, 1 °C-acclimated M. edulis had similar mitochondrial respiration as 1 °C-acclimated M. trossulus despite their different geographical origin. Our data indicate that mitochondrial capacity does not support latitudinal observed differences in whole animal metabolism between M. edulis and M. trossulus. However, we reveal that mitochondrial respiration in M. edulis can increase by 283% after cold acclimation. Combined, our results show that seasonal variation in mitochondrial respiration is of the same magnitude as large-scale (>1000 km) latitudinal variation. The high respiratory plasticity in Mytilus spp. improves fitness in changing temperature environments and supports their large biogeographic distribution. [ABSTRACT FROM AUTHOR]

In the present work we compared the type and frequency of gonadal abnormalities among Mytilus trossulus populations from the Gulf of Gdańsk, Baltic Sea. Observed histopathologies were grouped as regressive changes (RC, gonadal atresia (GA) and regression (GR)), progressive changes (PC, gonadal tumors) and intersex. Sex-based and spatial differences in frequency of RC were found, with the highest frequency of RC and PC found in mussels from polluted station B followed by mussels from station A located near a purification plant outlet. Bivalves from the reference area had the lowest frequency of RC. In order to confirm biomarker applicability of RC, an exposure experiment with model xenoestrogen 17α-ethinylestradiol (EE2) was performed. The exposure of M. trossulus to 50 and 500 ng dL − 1 of EE2 resulted in an increased frequency of gonadal regression and atresia, including melanized hemocytes infiltration in seminiferous tubules. We thus suggest that these changes can serve as biomarkers of endocrine disrupting compounds in biomonitoring studies. [ABSTRACT FROM AUTHOR]

While secondary contact between Mytilus edulis and Mytilus trossulus in North America results in mosaic hybrid zone formation, both species form a hybrid swarm in the Baltic. Despite pervasive gene flow, Baltic Mytilus species maintain substantial genetic and phenotypic differentiation. Exploring mechanisms underlying the contrasting genetic composition in Baltic Mytilus species will allow insights into processes such as speciation or adaptation to extremely low salinity. Previous studies in the Baltic indicated that only weak interspecific reproductive barriers exist and discussed the putative role of adaptation to environmental conditions. Using a combination of hydrodynamic modelling and multilocus genotyping, we investigate how oceanographic conditions influence passive larval dispersal and hybrid swarm formation in the Baltic. By combining our analyses with previous knowledge, we show a genetic transition of Baltic Mytilus species along longitude 12°-13°E, that is a virtual line between Malmö (Sweden) and Stralsund (Germany). Although larval transport only occurs over short distances (10-30 km), limited larval dispersal could not explain the position of this genetic transition zone. Instead, the genetic transition zone is located at the area of maximum salinity change (15-10 psu). Thus, we argue that selection results in weak reproductive barriers and local adaptation. This scenario could maintain genetic and phenotypic differences between Baltic Mytilus species despite pervasive introgressive hybridization. [ABSTRACT FROM AUTHOR]

Copper oxide nanoparticles (CuO-NPs) are among the most widely used metal oxide nanoparticles, which increases the chance of their being released into the marine environment. As the applications of these particles have increased in recent years, their potential impact on the health of marine biota has also increased. However, the toxicological effects of these NPs in the marine environment are poorly known. In the present study, the DNA damaging potential of CuO-NPs in the marine eastern mussel Mytilus trossulus was evaluated and compared to that of dissolved copper exposures. Genotoxicity was assessed by the single cell gel electrophoresis (comet) assay in mussel gill and digestive gland cells. The results showed that copper in both forms (CuO-NPs and dissolved copper) was accumulated to different extents in mussel tissues. The mussel exposed to the dissolved copper attained higher concentrations of copper in the gills than in the digestive gland. In contrast to these results, it was found that CuO-NPs could induce much higher copper accumulation in the digestive gland than in the gills. A clear and statistically significant increase in DNA damage was found in both tissues of the Cu-exposed group compared to the control mussels. Our results indicated that the CuO-NP exposure produced remarkable effects and increased DNA damage significantly in mussel gill cells only. It should be noted that the digestive gland cells were prone to accumulation following CuO-NPs when compared to the gill cells, while the gill cells were more sensitive to the genotoxic effects of CuO-NPs. These results also suggested the need for a complete risk assessment of engineered particles before its arrival in the consumer market. [ABSTRACT FROM AUTHOR]

Mussels have the ability to control biomineral production and chemical composition, producing shells with a range of functions. In addition to biological control, the environment also seems to influence the process of biomineralization; thus, shells can be used as archives of ambient water parameters during the calcium carbonate deposition. Past and present environmental conditions are recorded in the shells in the form of various proxies including Mg/Ca or Sr/Ca ratios. For such proxies to be accurate and robust, the influence of biological effects including the size of studied organism must be examined and eliminated or minimized, so that the environmental signal can be efficiently extracted. This study considers mineralogy and elemental composition of shells representing four size classes of Mytilus trossulus from the Baltic Sea. Obtained results suggest that mineralogy and chemical composition change throughout the shell development due to most likely a combination of environmental and biological factors. The content of aragonite increases with increasing shell size, while the bulk concentrations of Na, Cd, Cu, U, V, Zn and Pb were found to decrease with increasing height of the shells. Therefore, using mussels for environmental monitoring requires analysis of individuals in the same size range. [ABSTRACT FROM AUTHOR]

The accumulation of CuO nanoparticles causes destructive changes in the DNA molecule in the gill and digestive gland cells of the Pacific mussel Mytilus trossulus. The gill cells of the mollusk were found to be more sensitive to the genotoxic effect of CuO nanoparticles than the digestive-gland cells. [ABSTRACT FROM AUTHOR]