Marine stepping-stones: Connectivity of Mytilus edulis populations between offshore energy installations.

Recent papers have suggested that epifaunal organisms use artificial structures as stepping-stones to spread to areas that are too distant to reach in a single generation. With thousands of artificial structures present in the North Sea, we test the hypothesis that these structures are connected by water currents and act as an interconnected reef. Population genetic structure of the blue mussel, Mytilus edulis, was expected to follow a pattern predicted by a particle tracking model (PTM). Correlation between population genetic differentiation, based on microsatellite markers, and particle exchange was tested. Specimens of M. edulis were found at each location, although the PTM indicated that locations >85 km offshore were isolated from coastal subpopulations. The fixation coefficient FST correlated with the number of arrivals in the PTM. However, the number of effective migrants per generation as inferred from coalescent simulations did not show a strong correlation with the arriving particles. Isolation by distance analysis showed no increase in isolation with increasing distance and we did not find clear structure among the populations. The marine stepping-stone effect is obviously important for the distribution of M. edulis in the North Sea and it may influence ecologically comparable species in a similar way. In the absence of artificial shallow hard substrates, M. edulis would be unlikely to survive in offshore North Sea waters.

Ralstonia eutropha, containing high poly-ß-hydroxybutyrate levels, regulates the immune response in mussel larvae challenged with Vibrio coralliilyticus.

Marine invertebrates rely mainly on innate immune mechanisms that include both humoral and cellular responses. Antimicrobial peptides (AMPs), lysozyme and phenoloxidase activity, are important components of the innate immune defense system in marine invertebrates. They provide an immediate and rapid response to invading microorganisms. The impact of amorphous poly-ß-hydroxybutyrate (PHB-A) (1 mg PHB-A L-1) on gene expression of the AMPs mytimycin, mytilinB, defensin and the hydrolytic enzyme lysozyme in infected blue mussel larvae was investigated during "in vivo" challenge tests with Vibrio coralliilyticus (105 CFU mL-1). RNAs were isolated from mussel larvae tissue, and AMPs were quantified by q-PCR using the 18srRNA gene as a housekeeping gene. Our data demonstrated that AMPs genes had a tendency to be upregulated in challenged mussel larvae, and the strongest expression was observed from 24 h post-exposure onwards. The presence of both PHB-A and the pathogen stimulated the APMs gene expression, however no significant differences were noticed between treatments or between exposure time to the pathogen V. coralliilyticus. Looking at the phenoloxidase activity in the infected mussels, it was observed that the addition of PHB-A significantly increased the activity.

Large scale patterns in mussel beds: stripes or spots?

An aerial view of an intertidal mussel bed often reveals large scale striped patterns aligned perpendicular to the direction of the tide; dense bands of mussels alternate periodically with near bare sediment. Experimental work led to the formulation of a set of coupled partial differential equations modelling a mussel-algae interaction, which proved pivotal in explaining the phenomenon. The key class of model solutions to consider are one-dimensional periodic travelling waves (wavetrains) that encapsulate the abundance of peak and trough mussel densities observed in practice. These solutions may, or may not, be stable to small perturbations, and previous work has focused on determining the ecologically relevant (stable) wavetrain solutions in terms of model parameters. The aim of this paper is to extend this analysis to two space dimensions by considering the full stripe pattern solution in order to study the effect of transverse two-dimensional perturbations-a more true to life problem. Using numerical continuation techniques, we find that some striped patterns that were previously deemed stable via the consideration of the associated wavetrain solution, are in fact unstable to transverse two-dimensional perturbations; and numerical simulation of the model shows that they break up to form regular spotted patterns. In particular, we show that break up of stripes into spots is a consequence of low tidal flow rates. Our consideration of random algal movement via a dispersal term allows us to show that a higher algal dispersal rate facilitates the formation of stripes at lower flow rates, but also encourages their break up into spots. We identify a novel hysteresis effect in mussel beds that is a consequence of transverse perturbations.

Effect of ultra-sonication and its use with sodium hypochlorite as antifouling method against Mytilus edulis larvae and mussel.

Biofouling is a stubborn problem in cooling systems where using raw water from lakes, rivers, and sea. The effect of ultrasound and its sequential application with sodium hypochlorite (chlorination) upon marine bivalve Mytilus edulis (blue mussel), a massive fouling organism, has been studied and discussed here. The results obtained from the work carried out have shown that 42 kHz ultrasound is better than 28 kHz in accordance with veliger larvae mortality. The 42 kHz ultrasound has enhanced the mortality rate of veliger larvae than only free-residual chlorination up to 99%. On the other side, the 14-mm size mussel was less resistance than 25-mm size mussel to 42 kHz ultrasonication, among the studied two sizes (14 and 25 mm) of the blue mussel. Lethal time (100%) have decreased by 1-12% used for the sequential action of 42 kHz ultrasonic followed by free-residual chlorination compare with only free-residual chlorination treatment. The obtained results are put forward that the application of ultra-sonication before chlorination can reduce the mussel extinct time up to 12%. Obviously, this result will provide a possible use of ultra-sonication with famous chlorination antifouling treatment and eventually can decrease the chlorine exposure time and dose. It could discharge low chlorine by-products that may provide an environment friendly way.

Toxic dinoflagellates and Vibrio spp. act independently in bivalve larvae.

Harmful algal blooms (HABs) and marine pathogens - like Vibrio spp. - are increasingly common due to climate change. These stressors affect the growth, viability and development of bivalve larvae. Little is known, however, about the potential for interactions between these two concurrent stressors. While some mixed exposures have been performed with adult bivalves, no such work has been done with larvae which are generally more sensitive. This study examines whether dinoflagellates and bacteria may interactively affect the viability and immunological resilience of blue mussel Mytilus edulis larvae. Embryos were exposed to environmentally relevant concentrations (100, 500, 2500 & 12,500 cells ml(-1)) of a dinoflagellate (Alexandrium minutum, Alexandrium ostenfeldii, Karenia mikimotoi, Protoceratium reticulatum, Prorocentrum cordatum, P. lima or P. micans), a known pathogen (Vibrio coralliilyticus/neptunius-like isolate or Vibrio splendidus; 10(5) CFU ml(-1)), or both. After five days of exposure, significant (p < 0.05) adverse effects on larval viability and larval development were found for all dinoflagellates (except P. cordatum) and V. splendidus. Yet, despite the individual effect of each stressor, no significant interactions were found between the pathogens and harmful algae. The larval viability and the phenoloxidase innate immune system responded independently to each stressor. This independence may be related to a differential timing of the effects of HABs and pathogens.

Common European harmful algal blooms affect the viability and innate immune responses of Mytilus edulis larvae.

Like marine diseases, harmful algal blooms (HABs) are globally increasing in frequency, severity and geographical scale. As a result, bivalves will have to face the combined threat of toxic algae and marine pathogens more frequently in the (near) future. These stressors combined may further affect the recruitment of ecologically and economically important bivalve species as HABs can affect the growth, viability and development of their larvae. To date, little is known on the specific effects of HABs on the innate immune system of bivalve larvae. This study therefore investigates whether two common harmful algae can influence the larval viability, development and immunological resilience of the blue mussel Mytilus edulis. Embryos of this model organism were exposed (48 h) to five densities of Pseudo-nitzschia multiseries or Prorocentrum lima cells. In addition, the effect of six concentrations of their respective toxins: domoic acid (DA) and okadaic acid (OA) were assessed. OA was found to significantly reduce larval protein phosphatase activity (p < 0.001) and larval viability (p < 0.01) at concentrations as low as 37.8 µg l(-1). P. multiseries (1400 cells ml(-1)), P. lima (150 cells ml(-1)) and DA (dosed five times higher than typical environmental conditions i.e. 623.2 µg l(-1)) increased the phenoloxidase (PO) innate immune activity of the mussel larvae. These results suggest that the innate immune response of even the earliest life stages of bivalves is susceptible to the presence of HABs.

Effects of chemical contaminants on growth, age-structure, and reproduction of Mytilus edulis complex from Puget sound, Washington.

Bivalves are used as sentinel species to detect chemical contaminants in the marine environment, but biological effects on indigenous populations that result from chemical exposure are largely unknown. We assessed age-weight, length-weight relationships, age structure, and reproductive status (i.e. fecundity, egg size) of the blue mussel Mytilus edulis complex from six sites in central Puget Sound, Washington, and one site in the relatively pristine area of northern Puget Sound. Results of this study suggest that mussels from urban areas of Puget Sound exhibit a lower growth rate, altered population age-structure, and potential reproductive impairment as a result of exposure to chemical contaminants. These findings support the use of mussels as sentinel species to assess the biological effects of contaminants on invertebrate populations.

Effect of biofilm age on settlement of Mytilus edulis.

Biofilm ageing is commonly assumed to improve mussel settlement on artificial substrata, but the structure and taxonomic composition of biofilms remains unclear. In the present study, multi-species biofilms were characterized at different ages (1, 2, and 3 weeks) and their influence on settlement of the blue mussel, Mytilus edulis, was tested in the field. As biofilms can constitute a consistent food resource for larvae, the lipid quality, defined as the proportion of related essential fatty acids, may be a selection criterion for settlement. Overall mussel settlement increased on biofilms older than 1 week, and the enhanced settlement corresponded to the abundance and composition of the biofilm community, rather than to essential fatty acid levels. However, during a pulse of phytoplankton, the positive influence of biofilm was not detected, suggesting that pelagic cues overwhelmed those associated with biofilms. The influence of biofilms on mussel settlement could be more crucial when planktonic resources are limited.

Effects of ocean acidification on early life stages of shrimp (Pandalus borealis) and mussel (Mytilus edulis).

Ocean acidification (OA) resulting from anthropogenic emissions of carbon dioxide (CO(2)) has already lowered and is predicted to further lower surface ocean pH. There is a particular need to study effects of OA on organisms living in cold-water environments due to the higher solubility of CO(2) at lower temperatures. Mussel larvae (Mytilus edulis) and shrimp larvae (Pandalus borealis) were kept under an ocean acidification scenario predicted for the year 2100 (pH 7.6) and compared against identical batches of organisms held under the current oceanic pH of 8.1, which acted as a control. The temperature was held at a constant 10°C in the mussel experiment and at 5°C in the shrimp experiment. There was no marked effect on fertilization success, development time, or abnormality to the D-shell stage, or on feeding of mussel larvae in the low-pH (pH 7.6) treatment. Mytilus edulis larvae were still able to develop a shell in seawater undersaturated with respect to aragonite (a mineral form of CaCO(3)), but the size of low-pH larvae was significantly smaller than in the control. After 2 mo of exposure the mussels were 28% smaller in the pH 7.6 treatment than in the control. The experiment with Pandalus borealis larvae ran from 1 through 35 days post hatch. Survival of shrimp larvae was not reduced after 5 wk of exposure to pH 7.6, but a significant delay in zoeal progression (development time) was observed.

Heavy metals monitoring in the southernmost mussel farm of the world (Beagle Channel, Argentina).

Water quality surrounding the mussel farm of Mytilus edulis chilensis at Brown Bay (Beagle Channel) was evaluated. The levels of five heavy metals in sediment and in gill and digestive gland of mussels were examined to consider potential risks to human health. Cd showed the highest enrichment factor in relation to its level in Earth crust (3.85-21.58), which could be related to an upwelling phenomenon. A seasonal trend was found regarding metal bioaccumulation, being higher in winter than in summer. The bioaccumulation pattern in gill was Zn>Fe>Cu>Cd, meanwhile in digestive gland was Fe>Zn>Cu>Cd. Despite Pb was measured in sediment (15.59-23.91 microg/g dw), it was not available for being incorporated by mussels. In all cases it was below the detection limit (2.37 microg/g dw). With regard to human consumption of mussels from Brown Bay, none of the elements analyzed should cause concern for consumers. Values measured in tissue mussels were below the limit of 10 microg/g dw for Cd and Pb established by SENASA for molluscs. Considering that studied mussels are for human consumption and the relatively high levels of metals in sediment may vary their availability if physical parameters changes, periodical monitoring must be carried out to avoid human risks and to produce food in a responsible manner that complies with the food safety standards.

The ocean is not deep enough: pressure tolerances during early ontogeny of the blue mussel Mytilus edulis.

Early ontogenetic adaptations reflect the evolutionary history of a species. To understand the evolution of the deep-sea fauna and its adaptation to high pressure, it is important to know the effects of pressure on their shallow-water relatives. In this study we analyse the temperature and pressure tolerances of early life-history stages of the shallow-water species Mytilus edulis. This species expresses a close phylogenetic relationship with hydrothermal-vent mussels of the subfamily Bathymodiolinae. Tolerances to pressure and temperature are defined in terms of fertilization success and embryo developmental rates in laboratory-based experiments. In M. edulis, successful fertilization under pressure is possible up to 500 atm (50.66 MPa), at 10, 15 and 20 degrees C. A slower embryonic development is observed with decreasing temperature and with increasing pressure; principally, pressure narrows the physiological tolerance window in different ontogenetic stages of M. edulis, and slows down metabolism. This study provides important clues on possible evolutionary pathways of hydrothermal vent and cold-seep bivalve species and their shallow-water relatives. Evolution and speciation patterns of species derive mostly from their ability to adapt to variable environmental conditions, within environmental constraints, which promote morphological and genetic variability, often differently for each life-history stage. The present results support the view that a direct colonization of deep-water hydrothermal vent environments by a cold eurythermal shallow-water ancestor is indeed a possible scenario for the Mytilinae, challenging previous hypothesis of a wood/bone to seep/vent colonization pathway.

Transgenerational effects of short-term exposure to acidification and hypoxia on early developmental traits of the mussel Mytilus edulis.

Transgenerational effects of multiple stressors on marine organisms are emerging environmental themes. We thus experimentally tested for transgenerational effects of seawater acidification and hypoxia on the early development traits of the mussel Mytilus edulis. Fertilization rate, embryo deformity rate, and larval shell length were negatively impacted by acidification, while hypoxia had little effect except for increasing deformity rates under control pH conditions. Offspring from low pH/O2 parents were less negatively affected by low pH/O2 conditions than offspring from control parents; however, low pH/O2 conditions still negatively affected developmental traits in offspring from acclimated parents compared to control seawater conditions. Our results demonstrate that experimental seawater acidification and hypoxia can adversely affect early developmental traits of M. edulis and that parental exposure can only partially alleviate these impacts. If experimental observations hold true in nature, it is unlikely that parental exposure will confer larval tolerance to ocean acidification for M. edulis.

The blue mussel Mytilus edulis is vulnerable to the toxic dinoflagellate Karlodinium armiger-Adult filtration is inhibited and several life stages killed.

Blooms of the toxic dinoflagellates Karlodinium armiger and K. veneficum are frequently observed in Alfacs Bay, Spain, causing mass mortality to wild and farmed mussels. An isolate of K. armiger from Alfacs Bay was grown in the laboratory and exposed to adults, embryos and trochophore larvae of the blue mussel, Mytilus edulis. Adult mussels rejected to filter K. armiger at cell concentrations >1.5·103 cells ml-1. Exposure of adult mussels (23-33 mm shell length) to a range of K. armiger cell concentrations led to mussel mortality with LC50 values of 9.4·103 and 6.1·103 cells ml-1 after 24 and 48 h exposure to ~3.6·104 K. armiger cells ml-1, respectively. Karlodinium armiger also affected mussel embryos and trochophore larvae and feeding by K. armiger on both embryos and larvae was observed under the microscope. Embryos exposed to low K. armiger cell concentrations suffered no measurable mortality. However, at higher K. armiger cell concentrations the mortality of the embryos increased significantly with cell concentration and reached 97% at 1.8·103 K. armiger cells ml-1 after 29 h of exposure. Natural K. armiger blooms may not only have serious direct effects on benthic communities, but may also affect the recruitment of mussels in affected areas.

Blue mussel shell shape plasticity and natural environments: a quantitative approach.

Shape variability represents an important direct response of organisms to selective environments. Here, we use a combination of geometric morphometrics and generalised additive mixed models (GAMMs) to identify spatial patterns of natural shell shape variation in the North Atlantic and Arctic blue mussels, Mytilus edulis and M. trossulus, with environmental gradients of temperature, salinity and food availability across 3980 km of coastlines. New statistical methods and multiple study systems at various geographical scales allowed the uncoupling of the developmental and genetic contributions to shell shape and made it possible to identify general relationships between blue mussel shape variation and environment that are independent of age and species influences. We find salinity had the strongest effect on the latitudinal patterns of Mytilus shape, producing shells that were more elongated, narrower and with more parallel dorsoventral margins at lower salinities. Temperature and food supply, however, were the main drivers of mussel shape heterogeneity. Our findings revealed similar shell shape responses in Mytilus to less favourable environmental conditions across the different geographical scales analysed. Our results show how shell shape plasticity represents a powerful indicator to understand the alterations of blue mussel communities in rapidly changing environments.

Effects of temperature on scope for growth and accumulation of Cd, Co, Cu and Pb by the marine bivalve Mytilus edulis.

In many aquatic organisms including Mytilus edulis, the role of temperature on bioaccumulation of metals is still not clearly understood. In this study, uptake and accumulation of Cu, Co, Cd and Pb in mussels were investigated at different temperatures (6-26 degrees C). Results from exposure of isolated gills showed a positive relationship between temperature and metal uptake. But in whole organism experiments, only the accumulations of non-essential metals (Cd, Pb) showed a similar trend while the two essential metals Co and Cu were independent and inversely related to temperature, respectively. With exception of Cu, elimination process appeared to be independent of temperature. The study also showed that neither changes in scope for growth (SFG) of mussels nor chemical speciation could fully account for the observed temperature-effects. Overall, these results suggest that fundamentally (i.e. at epithelial membranes), temperature-effects on uptake are largely due to changes in solution chemistry and physical kinetics, which favours higher uptake at high temperature. But at whole organism level, complex physiological responses appears to mask the relationship, particularly for biologically essential metals like copper.

Life stage sensitivity of the marine mussel Mytilus edulis to ammonia.

Ammonia is an important contaminant to consider in all toxicity tests. It is especially important to consider the impacts of ammonia in test methods that use sensitive water column organisms exposed to sediments or sediment extracts, such as porewater and elutriate toxicity tests. Embryo-larval development toxicity tests, such as the 48-h method using Mytilus mussel species, are particularly sensitive to ammonia. To better understand the effect thresholds across different life stages of these mussels, 6 short-term (48-h) development toxicity tests and 3 21-d toxicity tests with different-sized juvenile mussels were conducted. Two of the juvenile mussel tests involved 21-d continuous chronic exposure to ammonia, whereas the third involved an acute 2-d ammonia exposure, followed by a 19-d recovery period. The embryo-larval development test method (50% effect concentration [EC50] = 0.14-0.18 mg/L un-ionized ammonia) was 2.5 times more sensitive than the juvenile mussel 21-d survival endpoint (50% lethal concentration = 0.39 mg/L un-ionized ammonia) and 2 times more sensitive than the most sensitive sublethal juvenile mussel endpoint (EC50 = 0.26 mg/L un-ionized ammonia). Further, it was found that the juveniles recovered from a 48-h exposure to un-ionized ammonia of up to 1.1 mg/L. The data generated suggest that the embryo development endpoint was sufficiently sensitive to un-ionized ammonia to protect the chronically exposed (21 d) juvenile mussels. Environ Toxicol Chem 2017;36:89-95. Published 2016 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Mixture toxicity in the marine environment: Model development and evidence for synergism at environmental concentrations.

Little is known about the effect of metal mixtures on marine organisms, especially after exposure to environmentally realistic concentrations. This information is, however, required to evaluate the need to include mixtures in future environmental risk assessment procedures. We assessed the effect of copper (Cu)-Nickel (Ni) binary mixtures on Mytilus edulis larval development using a full factorial design that included environmentally relevant metal concentrations and ratios. The reproducibility of the results was assessed by repeating this experiment 5 times. The observed mixture effects were compared with the effects predicted with the concentration addition model. Deviations from the concentration addition model were estimated using a Markov chain Monte-Carlo algorithm. This enabled the accurate estimation of the deviations and their uncertainty. The results demonstrated reproducibly that the type of interaction-synergism or antagonism-mainly depended on the Ni concentration. Antagonism was observed at high Ni concentrations, whereas synergism occurred at Ni concentrations as low as 4.9 µg Ni/L. This low (and realistic) Ni concentration was 1% of the median effective concentration (EC50) of Ni or 57% of the Ni predicted-no-effect concentration (PNEC) in the European Union environmental risk assessment. It is concluded that results from mixture studies should not be extrapolated to concentrations or ratios other than those investigated and that significant mixture interactions can occur at environmentally realistic concentrations. This should be accounted for in (marine) environmental risk assessment of metals. Environ Toxicol Chem 2017;36:3471-3479. © 2017 SETAC.

Mussel larvae modify calcifying fluid carbonate chemistry to promote calcification.

Understanding mollusk calcification sensitivity to ocean acidification (OA) requires a better knowledge of calcification mechanisms. Especially in rapidly calcifying larval stages, mechanisms of shell formation are largely unexplored-yet these are the most vulnerable life stages. Here we find rapid generation of crystalline shell material in mussel larvae. We find no evidence for intracellular CaCO3 formation, indicating that mineral formation could be constrained to the calcifying space beneath the shell. Using microelectrodes we show that larvae can increase pH and [CO32-] beneath the growing shell, leading to a ~1.5-fold elevation in calcium carbonate saturation state (Ωarag). Larvae exposed to OA exhibit a drop in pH, [CO32-] and Ωarag at the site of calcification, which correlates with decreased shell growth, and, eventually, shell dissolution. Our findings help explain why bivalve larvae can form shells under moderate acidification scenarios and provide a direct link between ocean carbonate chemistry and larval calcification rate.