The introduction of Pacific oysters to the sedimentary south-eastern North Sea coast and their establishment on intertidal native blue mussel beds has caused the development of mixed reefs of mussels and oysters with extensive tidepools. Tidepools have been intensively studied at rocky shores where they show community structures, which usually differ from that of the surrounding emerging substrates. Tidepools at sedimentary coasts, however, have received less attention. We compared the community structure and species interactions inside and outside tidepools in oyster reefs by determining densities of snails, barnacles and amphipods. Snail densities were similar in and outside tidepools. Barnacle coverage on bivalve shells, however, was lower inside tidepools, which may be caused by higher predation pressure and increased snail grazing under permanently submerged conditions, as was revealed by field and laboratory experiments. Additionally, we studied the occurrence of copepod and trematode parasites in blue mussels inside and outside tidepools. Prevalence and intensity of parasitic copepods was higher in mussels inside tidepools. Trematode parasites, by contrast, showed a lower intensity in mussels inside tidepools. This can be explained by high amphipod densities found inside tidepools because trematode larvae represent a food source of amphipods. Our study suggests that the community structure of oyster reefs within tidepools is not a submerged equivalent to that of intertidal reefs. As their counterparts at rocky shores, they show their own species distribution patterns with particular species interactions and only provide refuge for specific species such as parasitic copepods.

Currently, there is little comparative data on ‘efficiency’ of different engineering species, i.e. species richness, density and biomass of the associated organisms that have been supported by engineering species. The use of fouling communities makes it possible to compare the efficiency of different engineering species under the same conditions, which is necessary to obtain correct estimates and difficult to do when studying natural bottom communities. In this study, we have analysed the fouling communities in four different mussel culture farms in the White Sea to test the following hypotheses. (1) Different engineering species (mussel Mytilus edulis, solitary ascidian Styela rustica, sponge Halichondria panicea) have different assemblages of the associated vagile fauna. (2) Mytilus edulis is the most efficient engineering species, i.e. species richness, species diversity, density and biomass of the associated vagile fauna is higher in the mussel communities than in those dominated by Styela rustica or Halichondria panicea. The first hypothesis was confirmed, while the second was rejected. In all the culture farms studied, all parameters of the mussel-associated vagile fauna were not higher and in most cases were even lower than those of the fauna associated with ascidians or sponges. The reason for this seems to be the very dense packing of mussels in patches. Therefore, Mytilus edulis is not the most efficient engineering species among fouling organisms, at least in the conditions of the subarctic White Sea. The data obtained are particularly important in view of the ever-increasing volume of anthropogenic substrate and fouling communities in coastal marine ecosystems.

Accelerator mass spectrometry (AMS) radiocarbon (14C) dating of Cerastoderma edule (Linnaeus 1767) and Mytilus edulis (Linnaeus 1758) shells sampled in AD 1889 near the island of Wangerooge gave a new local correction factor ΔR of −85 ± 17 14C years for the Wadden Sea area. The value is considerably higher than the available scattered data from the North Sea, which were obtained from pre-bomb growth rings of living Arctica islandica (Linnaeus 1767). This can be explained by the incorporation of 14C-depleted terrestrial carbon into the shell material which compensates the intensified exchange of CO2 between atmosphere and shallow coastal water, e.g. by tidal currents. Additionally, two examples of application of the new ΔR value in coastal research give deeper insights into the dynamics of bivalve shell preservation in the Wadden Sea and the need for further research to clarify the Holocene reintroduction of Mya arenaria (Linnaeus 1758) into European waters.

Cardiac activity of two White Sea Bivalvia species – Mytilus edulis and Modiolus modiolus – was monitored in situ for one full calendar year every 4 days. During the year, we also assessed the temperature and salinity of the ambient seawater (at intervals of 1 min), measured phytoplankton concentration (every 4 days) and checked the reproductive status of the molluscs (every 2 weeks). Our field study showed a significant linear correlation between the molluscs’ heart rates and the temperature of the ambient seawater. However, during specific periods of the year, we observed that phytoplankton composition or reproductive status became the dominant influence over cardiac activity. Phytoplankton concentrations were generally found to be low throughout the entire year, but two peak periods of drastically elevated phytoplankton concentration were found (April and May), and during April the peak heart rates of the blue mussels significantly increased. Spawning time took place in the middle of June, and at this time the cardiac activity of the molluscs did not change in spite of a 4°C temperature increase in the ambient seawater. Monitoring of the heart rates of the real intertidal blue mussels (animals located at the middle part of intertidal) revealed periodic fluctuations in cardiac activity that correlated strongly with tidal fluctuations. Cardiac activity in M. modiolus was significantly lower than in M. edulis from 9 May to 25 November. On the basis of our data, we concluded that the molluscs’ cardiac activity can serve not only as an indicator of the animals’ physiological conditions, but also as an indicator of changes in ambient factors.

Marteilia refringens causes marteiliosis in oysters, mussels and other bivalve molluscs. This parasite previously comprised two species, M. refringens and Marteilia maurini, which were synonymized in 2007 and subsequently referred to as M. refringens ‘O-type’ and ‘M-type’. O-type has caused mass mortalities of the flat oyster Ostrea edulis. We used high throughput sequencing and histology to intensively screen flat oysters and mussels (Mytilus edulis) from the UK, Sweden and Norway for infection by both types and to generate multi-gene datasets to clarify their genetic distinctiveness. Mussels from the UK, Norway and Sweden were more frequently polymerase chain reaction (PCR)-positive for M-type (75/849) than oysters (11/542). We did not detect O-type in any northern European samples, and no histology-confirmed Marteilia-infected oysters were found in the UK, Norway and Sweden, even where co-habiting mussels were infected by the M-type. The two genetic lineages within ‘M. refringens’ are robustly distinguishable at species level. We therefore formally define them as separate species: M. refringens (previously O-type) and Marteilia pararefringens sp. nov. (M-type). We designed and tested new Marteilia-specific PCR primers amplifying from the 3’ end of the 18S rRNA gene through to the 5.8S gene, which specifically amplified the target region from both tissue and environmental samples.

The Renicolidae are digenean parasites of piscivorous and molluscivorous birds. Although they exhibit few morphological autapomorphies and are highly variable, the numerous suggested re-classifications within the family have never been supported by any molecular analyses. We address the possible synonymization of species within the Renicola pinguis complex suggested previously by Odening. We provide and analyse sequences of two nuclear (ITS2, 28S rDNA) and two mitochondrial (CO1, ND1) DNA loci of central European species of the Renicolidae, namely Renicola lari, Renicola pinguis and Renicola sternae sp. n., and we also provide first sequences of Renicola sloanei. The combined molecular and comparative morphological analysis confirms the previously questioned validity of the three Renicola spp. of highly similar morphology, which display strict niche separation in terms of host specificity and selectivity. We identify two previously unreported clades within the genus Renicola; however, only one of them is supported by the analysis of adult worms. We also provide comparative measurements of the three examined closely related central European renicolids, and describe the newly proposed tern-specialized species Renicola sternae sp. n., which was previously repeatedly misidentified as Renicola paraquinta. Based on the extensive dataset collected in 1962–2015, we update the host spectrum of Renicolidae parasitizing central European birds (Renicola bretensis, R. lari, Renicola mediovitellata, R. pinguis, Renicola secunda and R. sternae sp. n.) and discuss their host-specific prevalence and intensity of infections.

The annual gametogenic cycle in the blue mussel, Mytilus edulis L. was investigated from May 2010 to May 2011 in two locations in north-western Iceland. Food availability (chlorophyll-a) was high in early spring at both sites, with a summer maximum in July in Steingrimsfjördur but an autumn maximum in September in Patreksfjördur. Gonad development started in November at both sites, with ripe gametes still visible in the follicles, and continued throughout the year, except for a very short time prior to spawning in Steingrimsfjördur. Gametes developed mostly between November and May. Spawning was protracted, lasting from July to early winter at both sites. The main spawning events occurred from August (11.7°C) to October (9.4°C) in Patreksfjördur, but from July (9.8°C) to October (8.6°C) in Steingrimsfjördur

The trematode Parorchis acanthus is widely distributed and exhibits a broad host spectrum, with larval stages occurring in marine gastropods and adult flukes parasitizing on various seabird species. Unlike the majority of digeneans, its cercariae do not invade a second intermediate host but encyst on a substrate in the open. In a series of laboratory experiments, we investigated factors influencing cercarial emergence and settlement of P. acanthus. Emergence of cercariae from the gastropod intermediate host Nucella lapillus increased with increasing temperature, whereas cercarial encystment success decreased. Numbers of emerged cercariae were highest in the presence of light and water. However, although in much lower numbers, cercariae were also released from N. lapillus and successfully encysted under relatively dry conditions. Cercariae were found to settle predominantly on filtering blue mussels Mytilus edulis, suggesting that cercarial concentration on the valves is largely facilitated by the bivalve's inhalation current. After being inhaled, cercariae actively emerged from the mussels using their suckers and subsequently encysted on the shells, preferably along the rim of the valves. Barnacle epibionts Semibalanus balanoides were observed to impair cercarial settlement on mussels, by disturbing or preying on cercariae. Whilst settlement success of cercariae on M. edulis increased with increasing mussel density, intensity of encysted metacercariae decreased. Furthermore, cercariae settled more efficiently on small than on large mussels. Our findings suggest that the transmission of P. acanthus cercariae is regulated by a range of abiotic and biotic factors, with filtering activity of mussels playing a key role by enhancing accumulation of cercariae on a substrate suitable for transmission to the bird final host.

Sexual maturation and spawning was followed in one and two year old rope cultured mussels (Mytilus edulis) from April to December. Development of gonad and storage tissue was followed using descriptive categories from histology, and development of total soft tissue was followed using meat yield and condition index.

Both age groups were mature both during spring and autumn and had similar patterns of spawning and maturation. April and May were characterized by scattered spawning activity and accumulation of storage reserves at the same time, resulting in relative constant condition indices during this period. This was followed by ripening of the gonads and an increase in condition index that culminated in a spawning in late June. Parts of the population then entered a resting phase, while a part of the population underwent new maturation towards an autumn spawning in September. In December all the mussels had started the winter maturation.

Condition index and meat yield were higher throughout the season in the one year old mussels. This was probably due to the sum of several factors, including differences in specific feeding rates and biomass density, rather than spawning.

The present study is the first to compare the reproductive patterns over time of one and two year old mussels with reliable age determination, and provide information that there are no obvious differences in neither timing of gonad development nor spawning patterns between the age-classes.

The blue mussel, Mytilus edulis, and the Mediterranean mussel, Mytilus galloprovincialis, occur widely over much of northern Europe, and wherever they are sympatric they hybridize. The hybrid zone is large, ranging from western France to the north of Scotland, and is spatially complex, containing a mixture of pure, hybrid and introgressed individuals. Results from an Irish study in 1981, using partially diagnostic allozyme markers, indicated that mussels on the Irish Sea coast were solely M. edulis, but on Atlantic wave-exposed shores, and to a much lesser extent on wave-protected shores, mussels comprised an interbreeding mixture of M. edulis and M. galloprovincialis. In this study mussels were analysed from 20 locations on Irish coasts, using the Me15/16 nuclear DNA marker. The results showed a high frequency of M. galloprovincialis (0.378 ± 0.198) and hybrid (0.429 ± 0.175) genotypes, and correspondingly low frequencies of the M. edulis genotype (0.194 ± 0.107) at both exposed and sheltered locations on Atlantic coasts, indicating no apparent advantage for the M. edulis genotype at wave-protected sites. Mytilus galloprovincialis was virtually absent from the Irish Sea. Mussels in this area may be a self-recruiting population of M. edulis due to thermal front development at the northern and southern entrances to the Irish Sea in late spring, thereby preventing an influx of spring-spawned Mytilus larvae. The apparent change in the genetic composition of mussels on Atlantic coasts since the early 1980s could be related to climate change, or to aquaculture practice in Ireland whereby mussels from exposed shores are used to seed ropes in wave-protected bays and estuaries.

The occurrence of new phytoplankton species in a coastal area may be explained by the import of shellfish containing whole live algal cells in their digestive tracts. Indeed, shellfish containing toxic algal cells can induce both primary contaminations in safe areas (initially free from toxic microalgae), and secondary contaminations of other shellfish growing in the same area via the faeces of the imported animals. To mitigate this problem, shellfish need to be placed in a separate holding tank and their intestinal content purged. For a deeper understanding of the risks associated with transferring contaminated shellfish, oysters (Crassostrea gigas) and mussels (Mytilus edulis) were purposely fed either Alexandrium minutum or A. catenella (Dinophyceae) or Pseudo-nitzschia calliantha (Bacillariophyceae) toxic algae for 2 h. They were then transferred into individual tanks where they were continuously fed with a non-toxic alga, Tetraselmis suecica. Biodeposit production, faeces composition, and filtration rates were monitored for the shellfish over a 6-h period. The effect of temperature differences and different initial toxic algae concentrations were compared. This study revealed a relationship between temperature and cell lysis in the oyster digestive tract. It also indicated that toxic algae concentration did not seem to influence gut passage time in oysters, while a significant effect was observed in mussels, and confirmed the existence of a difference between oyster and mussel feeding patterns.

The petroleum spilt by the tanker “Erika” contained environmentally high concentrations of nickel (45 mg kg−1) and vanadium (83 mg kg−1). Our aim was to show that nickel and vanadium concentrations in marine organisms could be used as tracers of their exposure to oil deposits along the coast. Two biomarkers were determined, condition index (CI) and metallothionein levels.Samples were collected monthly from January to May 2000 from five sites along the coast of Vendée and Loire Atlantique: (1) Lérat, (2) La Govelle, (3) Saint Gildas, (4) La Bernerie and (5) La Fosse. Among benthic invertebrates, mussels Mytilus edulis (filter-feeders), periwinkles Littorina littorea (grazing-feeders) and dogwhelks Nucella lapillus (carnivora, bivalve predators) were selected. In addition, mussels were collected from a control site, Fier d'Ars (Ré Island). The species chosen as bioindicators have responded to the presence of oil in their environment by accumulating nickel and vanadium. The bioaccumulation of vanadium occurred early one month after oil spill whereas nickel bioaccumulation was deferred, probably as a consequence of a lower stability of vanadylporphyrins compared to nickelporphyrins which are known in particular for their role in stabilizing emulsions (film at the water/oil interface). Interspecific differences may be explained by different food habits: periwinkles grazed contaminated algae; mussels as filter-feeders retained particles and colloids from the water column; dogwhelks fed on mussels. Spatio-temporal changes of nickel and vanadium concentrations may result from (i) the arrival of new oil slicks, (ii) the action of cleaning of the coasts contributing to the re-suspension of petroleum. In all of the three species, few changes of the CI were observed from site to site. CI variations were linked to sexual ripening in mussels. Mussels originating from the control site showed MT concentrations significantly lower than those in specimens from impacted sites. The highest MT concentrations were observed in January and February, and then a consistent decrease was registered in March and May. MT concentrations in periwinkles increased very significantly in March and May. An increase in MT concentrations was also shown at this period in dogwhelks. Depending on the species, positive correlations were shown between MT and nickel and/or vanadium concentrations.

A 3-year survey was made of several biological markers in mussels (Mytilus edulis) exposed in situ to the oil that came ashore after the wreck of the “Erika” tanker on the Brittany (France) coast in December 1999. The mussel response was assessed using a set of 7 biomarkers, most of them related to the metabolism of organic contaminants. After a series of validation tests, data was evaluated for only 5 biomarkers: acetylcholinesterase (AChE), glutathione S-transferase (GST), catalase (CAT), malondialdehyde (MDA) and deoxyribonucleic acid (DNA) adducts. No significant reductions in GST or CAT levels were observed, levels of DNA adducts and MDA were high during the 6 months immediately following the accident and levels of AChE were significantly lower during the first year of the survey suggesting a general stress. A simple multivariate graphic method, the integrated biomarker response index, was used to combine 4 of the 5 validated biomarkers and quantify the degree of impact on mussels at different sites. The results show that mussel populations were affected by the oil spill only during the first year after the event.

Anti-Bacillus megaterium activity was measured in unfractionated plasma withdrawn from three common US East Coast bivalve molluscs: an oyster Crassostrea virginica and the mussels Geukensia demissa and Mytilus edulis. The activities of the plasma samples from these bivalves were also measured against a C. virginica pathogen Perkinsus marinus. Strong anti-B. megaterium activity was measured in plasma from C. virginica and M. edulis, but was not detected in G. demissa. Bactericidal activity was found in hemocyte extracts from all bivalves in this study, suggesting a cellular origin of cytotoxic humoral factors. Peptides (< 10 kDa) were separated from the plasma samples by ultrafiltration; weak antibacterial peptide activity was quantified in C. virginica peptides, but not in peptides from the mussels. In the case of P. marinus, plasma from M. edulis or G. demissa was boldly cidal as compared to plasma from C. virginica. This difference in activity probably reflects the low pathogenicity of this oyster parasite for the mussel species tested. In summary, the bactericidal activity of plasma proteins from these bivalves showed considerable interspecies variation and did not necessarily correlate directly with antiprotistan activity. When present, antibacterial and antiprotistan activities seemed to be associated with plasma proteins rather than < 10-kDa plasma peptides, with the possible exception of C. virginica anti-B. megaterium activity and the occasionally expressed anti-P. marinus activity of M. edulis peptides. The precise identity of the plasma protein(s) responsible for the antimicrobial activities measured have yet to be determined, but it is likely that agents other than, or in addition to, lysozyme play significant roles in the process.

Haemocytes of Mytilus edulis, allowed to attach to the plastic surface of a tissue culture plate in the presence of haemolymph, were observed by time-lapse video recording. When bacteria were added at concentrations of 10 or 50 bacteria per haemocyte, certain bacterial strains caused rounding of the cells within 2–3 h. Haemolymph was necessary for the rounding to occur; if bacteria were added in sterile seawater there was no significant difference in the number of rounded cells between control and bacteria-treated cultures for up to 4 h. The haemolymph factor required for this activity was active at 1/64 dilution in seawater, was sensitive to trypsin treatment, and activity was halved on heating at 56 or 100 °C for 30 min. For the most toxic bacteria tested, Vibrio alginolyticus NCMB 1339 and Vibrio anguillarum A7, haemocyte cell rounding appeared to be induced by a very small number of bacterial cells. Bacteria-free culture supernatant of V. anguillarum 2981 induced rounding of haemocytes in a dose-dependent manner, with 50 % of cells being rounded at a dilution of approximately 1/500 of the culture supernatant. In a survey of 226 bacterial isolates, those isolated from incidents of disease in a bivalve hatchery were significantly more toxic towards haemocytes than bacteria isolated from hatcheries without disease or from turbot hatcheries.

Most recent authors have called the Chilean blue mussel (formerly Mytilus chilensis) Mytilus edulis. Mussels from four nominal species (Mytilus edulis, M. trossulus, M. galloprovincialis and M. chilensis) were collected from the eastern coast of Newfoundland, Canada, New Zealand and the southern coast of Chile. Canonical discriminant analysis of selected shell morphometrical characters showed that although there is some overlap in canonical variates, the three nominal species, M. edulis, M. trossulus and M. chilensis can be morphologically divided into three distinct groups. The two nuclear-DNA markers (ITS and Glu-5) and the mtDNA marker studied indicate that the nuclear and mitochondrial genomes of M. edulis and M. trossulus are different. M. edulis, M. galloprovincialis and M. chilensis share similar restriction fragment patterns for the mtDNA and for the ITS nuclear-DNA marker, while the Glu-5 polymerase chain reaction (PCR) assay showed that the M. edulis and M. chilensis genotypes disagree, producing species-specific banding patterns that can be used as a diagnostic marker between the two nominal species. The molecular and morphometric data reported here give more evidence to support the view of other authors that the Chilean blue mussel should be included as M. edulis subspecies: Mytilus edulis chilensis.

Results are presented from laboratory-based experiments in which we investigated short-term responses of Mytilus edulis L. to experimental changes in the amount and composition of suspended seston. Working with large quantities of cultured algae, we have studied feeding behaviour over ranges of food availability and quality that extend well beyond earlier limits. Findings confirm the ability of mussels to selectively reject inorganic particles as pseudofaeces prior to ingestion, thereby enriching the organic content of ingested matter by 30% more than the organic content of natural filtered seston. Our findings also establish acclimation both of selective and absorptive processes, indicating that the extent to which growth of M. edulis can be stimulated in the short-term will depend upon prior nutritional history. Present maximal growth of 14.8% dry soft tissue d−1 in a standard M. edulis of 1 g dry soft tissue was much higher than has previously been documented for any adult mussel. Maximal growth was achieved when natural seston that had been enriched to more than about 60% organic content with a mixture of algal monocultures was available at concentrations above about 11.5 mg total particulates 1−1. Neither ingestion rate nor net energy balance were improved with further increases in food availability, associated with regulatory reductions in the rate of water filtration (clearance rate) that maintained organic ingestion rate independent of increases in both the amount and organic content of available seston. These findings suggest that digestive processes had become saturated when organic ingestion reached about 6.5 mg organics g−1 dry soft tissue h−1 in a standard M. edulis of 1 g dry soft tissue, representing as much as 20.6% of all soft tissue organic mass mussel−1 d−1. Such saturation of organic ingestion is consistent with previous conclusions based on comparative allometries showing that limitations to growth in M. edulis and other bivalves are associated with the rate of food processing.

De nombreux travaux portant sur l'absorption directe et l'utilisation métabolique des substances organiques dissoutes et en particulier les acides aminés libres chez les larves de bivalves ont été entrepris ces dernières années. En ce qui concerne le glucose, constituant majeur des sucres dans le milieu marin, les résultats obtenus jusqu'à présent ont porté essentiellement sur les mécanismes d'absorption des larves d'invertébrés marins. Dans ce travail on étudie le rôle trophique du glucose dissous dans la nutrition des véligères de Mytilus edulis. En présence d'algues Phaeodactylum tricornutum, le glucose à des concentrations de 5.6 et 56 nmol/dm3 augmente le taux de filtration de 26 % et le taux d'ingestion de 10 %. Au contraire, aux fortes concentrations de 2,8 μmol/dm3 on assiste à une réduction du taux de filtration de 18 % et du taux d'ingestion de 10 %. De plus, l'utilisation de deux traccurs (algues marquées au 14C et glucose marqué au 3H) a permis de constater que la diminution de l'ingestion de cellules, observée en présence de 2,8 μmol/dm3 est accompagnée d'une augmentation d'absorption de glucose. A 2,8 μmol/dm3, sa contribution énergétique est estimée à 11,6 % du coût énergétique total correspondant à 34.5 % de l'énergie de la respiration. Cela met en évidence le rôle métabolique du glucose dissous lorsque les larves n'ont pas suffisament de cellules algales vivantes à leur disposition.