Late Pleistocene and Holocene distribution of Mytilus edulis in the Barents Sea region and its palaeoclimatic implications

Aim For decades, subfossil shells of the bivalve Mytilus edulis Linnaeus, 1758 in Svalbard have been taken as evidence of higher surface temperatures during the early Holocene because the modern northern occurrence of this mollusc was, until recently, in the southern Barents Sea. Here, we elucidate and discuss the spatial and temporal Late Pleistocene and Holocene distribution of the species within the entire Barents Sea region. Location The Barents Sea region. Methods Radiocarbon dates of Mytilus shells from the Barents Sea region and information about the present distribution of the species were compiled, including two new radiocarbon dates from north‐eastern Spitsbergen. The dataset was divided into time slices, each covering 1000 years, and compared with Holocene temperature variations, ocean current systems and present‐day temperature patterns. Results Maps show the Late Pleistocene and Holocene spatial and temporal distribution of Mytilus edulis in the Barents Sea region. M. edulis was already present in northern Norway about 14,000 cal. yr bp . It appeared at western Spitsbergen about 11,000 cal. yr bp , and slowly spread to the rest of the archipelago. The maximum distribution in the region was reached 10,000–7000 cal. yr bp , coinciding with the Holocene climatic optimum. The species gradually disappeared in the late Holocene and became absent from the northern and eastern parts of the region 3000–1000 cal. yr bp . Today, M. edulis lives in the southern part and has begun to recolonize the northern parts. Main conclusions The time slices illustrate strong connections between the ocean current regimes, the climate and the distribution of M. edulis. The species settled in the southern part of the Barents Sea region several thousand years before it spread to the northern part during the Holocene climatic optimum. It may even have been completely absent from the region for a short time during the late Holocene cold period. The Holocene distribution of Mytilus implies that the underlying pattern of coastal sea surface temperatures in the region was very stable.     

Salinity related physiological and genetic differences between populations of Mytilus edulis

Aminopeptidase-I, the enzymatic product of the Lap locus, liberates N-terminal neutral and aromatic amino acids from oligopeptides. The enzyme is associated with the brush border of the intestine and the extensive lysosomal system in the digestive tubule cells; the enzyme functions in oligopeptide degradation and possibly amino acid transport. The Lap locus is genetically polymorphic and allele frequencies differ between populations according to environmental salinities.
Using cell-free lysosomes, we show salinity related differences in both lysosomal membrane latency and lysosomal and cytosolic free-amino acid concentrations. Differences in the response of the lysosomal aminopeptidase-I enzyme to differences or changes in salinity are discussed.
Antibodies against aminopeptidase-I enzyme were used to demonstrate that alleles of the Lap locus exhibit different specific activities per unit enzyme concentration. In oceanic populations, the concentrations of aminopeptidase-I enzyme of individual phenorypes are equal, suggesting that variation of specific activity among phenorypes is due to allele specific differences in catalytic efficiency. In estuarine populations, total enzyme activity is lower, which is partially due to a significantly lower concentration of aminopeptidase-I enzyme of one homozygote genotype.
The consequences of a change in environmental salinity can be measured on the biochemical, physiological, and population genetic levels. We discuss the possible mechanisms by which salinity variations are responsible for the genetic polymorphism of aminopeptidase-I.     

The ecophysiological response of mussels (Mytilus edulis) in mesocosms to a range of inorganic nutrient loads: simulations with the model EMMY

EMMY is an ecophysiological model of the growth and reproduction of a single mussel (Mytilus edulis L.). It contains feedback loops in the uptake and metabolism of food and in the partitioning of carbon and nitrogen to the internal state variables somatic tissue, storage, organic shell matrix and gametes. In this paper EMMY is used to simulate individual mussel growth in a series of mesocosm experiments with different inorganic nutrient loads (N and P). The experiments explore the impact of eutrophication reduction scenarios on mussel growth under defined and controlled conditions.In earlier studies EMMY was calibrated using expert knowledge on growth and reproduction during a period of 5 years. The resulting calibrated model was validated for system inputs and observations of three ecosystems with significantly different food and silt concentrations. EMMY reproduced the mussel growth sufficiently accurate in ecosystems with moderate or high food concentrations. In this study EMMY was adapted in order to cope with low food concentrations, then recalibrated (using the original calibration data and procedure) and applied without further calibration to 3 replicated mesocosm experiments. The EMMY simulations in this study show the ecophysiological response of mussels to different food (phytoplankton and detritus) concentrations. It is concluded that the mussels can adapt to significantly reduced food concentrations, due to inorganic nutrient load reduction, and still maintain growth.     

Genetic studies of laboratory reared mussels, Mytilus edulis: heterozygote deficiencies, heterozygosity and growth

Offspring derived from several single pair matings and a mass mating of Mytilus edulis were cultured up to the juvenile stage in the laboratory. Samples were collected from the cultures at an early post- settlement ('spat') stage and again at the juvenile stage and were scored at up to nine enzyme loci using cellulose acetate and starch gel electrophoresis. An overall significant deficiency of heterozygotes was evident at the juvenile stage but not at the spat stage. Selection against heterozygotes (underdominance) is proposed as the cause.
For each mating, shell lengths of juvenile mussels were measured and individuals were classed according to the number of loci at which they were heterozygous. No significant correlations were evident between heterozygosity class and either growth (shell length), or coefficient of variation of shell length. It is argued that these results provide support for the 'associative overdominance' rather than the 'overdominance' hypothesis as an explanation for heterozygosity/growth correlations in marine bivalves.
These data also show that although heterozygosity and growth co-occur in most data sets from natural populations, they may have distinctly differing causes.     

Quantification of mussel (Mytilus edulis) growth from power station cooling waters in response to chlorination procedures

The age and growth history of individual mussels collected from the cooling water culverts of a power station were determined from the growth bands present in acetate peels of polished and etched shell sections. During periods of exposure to the antifouling agent, sodium hypochlorite (0.2mgl^‐1), shell growth was severely reduced, resulting in marked changes in the structure and deposition of the shell. As a consequence of chlorination, the growth rate of the mussel population occurring within the culverts was substantially lower and the mean length‐at‐age significantly smaller than that of a naturally occurring population immediately outside the cooling water intake. The growth patterns present in the shells of mussels experimentally added to the cooling waters during chlorination were compared with, and found to be similar to, the patterns in the shells of mussels that had settled naturally in the culverts. The daily growth of the experimentally exposed mussels (1.1–5.2 μm d^‐1) is two orders of magnitude lower than the growth rate of mussels growing in untreated waters. The use of mussels for evaluating the efficiency and long‐term effects of low level chlorination is discussed.     

Phenoloxidase (E.C. 1.14.18.1) from the byssus gland of Mytilus edulis: Purification,partial characterization and application for screening products with potential antifouling activities

Although a total ban on the use of TBT coatings is not expected in the short term, there is a growing need for environmentally safe antifouling systems. To assist in the rapid screening of a large number of potential antifouling substances, a method that is simple, efficient and inexpensive is required. The production of byssus threads by the blue mussel, Mytilus edulis, has often been studied for testing the antifouling efficacy of various compounds. The present study reports a new antifouling assay based on the inhibition of purified M. edulis phenoloxidase activity. The method has the advantage of being specific, reliable, sensitive and rapid.     

A new approach for the assessment of stochastic variation: analysis of behavioural response in blue mussel (Mytilus edulis L.)

One of the most effective techniques for evaluating stress is the analysis of developmental stability, measured by stochastic variation based particularly on fluctuating asymmetry, i.e. a variance in random deviations from perfect bilateral symmetry. However, the application of morphological methods is only possible when an organism lives under testing conditions during a significant part of its ontogenesis. Contrary to morphological characters, behavior can change very fast. Consequently, methods based on behavioural characters may have advantages over more traditional approaches. In this study we describe the technique of assessing stochastic variation, using not morphological, but behavioural characters. To measure stochastic variation of behavioural response, we assessed the stability of the isolation reaction of blue musselMytilus edulis at regular changes of salinity. With increasing temperature from +12°C to +20°C stochastic variation of the isolation reaction increased, which is a common response to change of environmental conditions. In this way, we have developed a method of assessing stochastic variation of behavioural response in molluscs. This method may find a great range of applications, because its usage does not require keeping animals in tested conditions for a long time.     

Microbial biomass and activity in the vicinity of a mussel bed built up by the blue mussel Mytilus edulis

Our study focuses on the impact of the biosedimentary system mussel bed (Mytilus edulis) on the spatial variability of benthic microbial biomass and activity in relation to organic deposits. We sampled a transect of six stations from the muddy mussel bed towards a reference station in the sandflat in monthly intervals for 1 year. The sediment grain size fraction <63 μm and the total organic carbon (TOC) concentration decreased significantly towards the sandflat. Bacterial numbers and total microbial biomass (total adenylates) showed a high spatial variability and were not correlated to increasing distance from the mussel bed. However, a significant relationship with the TOC concentration was found. In contrast, the energetic status (adenylate energy charge) of the microbial community in the mussel bed was significantly lower than in the sandflat. A principal component analysis of the substrate-utilization pattern revealed clear differences between the microbial communities in the mussel bed and in the sandflat. Our results indicate that the sandflat may be dominated by a relatively specialized benthic microbial community with an increased efficiency in utilizing organic carbon sources. As a disadvantage, however, such r-strategists are only able to meet environmental changes within a comparatively narrow range. Benthic microbial communities in the vicinity of an M. edulis mussel bed, in contrast, are dominated by relative generalists with a greater physiological capacity to buffer discrete environmental changes. Such K-strategists show a lack of specialization which generally means a reduced efficiency in utilizing a particular resource. Received: 2 May 1999 / Received in revised form: 22 November 1999 / Accepted: 6 December 1999     

On the dynamics of the stocks of blue mussels (Mytilus edulis L.) in the Danish Wadden Sea

As biological basis for the monitoring programme for the commercially exploited stock(s) of mussels (Mytilus edulis L.) in the Danish Wadden Sea, samples of mussels have been collected regularly since 1986, both from sub-tidal and inter-tidal mussel beds. These samples are the basis for the estimation of total biomass. They also provide data on size frequency distributions, which have been analysed for cohort identification resulting in length at age data, which again have been used for estimating parameters (L and K) for the von Bertalanffy growth equation (VBGE) as well as mortality parameters. By applying these in the Beverton & Holt model, estimates of average biomass and annual production (P) of the mussels have been obtained together with possible fisheries yields from the beds. The growth and mortality parameters and the figures for annual production and P/B are compared with figures from other investigations. These analyses have been the basis for annual assessments of the mussel stocks, which again are used in the current management of mussel fishery in the Danish Wadden Sea.     

Short-term impact of blue mussel dredging (Mytilus edulis L.) on a benthic community

The short-term effect of mussel dredging in a brackish Danish sound was studied. A commercial dredging track was identified and an analysis of the species composition inside the track and at an adjacent control area showed that dredging changed the community structure by reducing the density of polychaetes. In order to investigate the extent and the duration of the dredging impact experimental dredging was conducted. The experimental dredging removed 50% of the mussels in two dredged areas. Immediately after dredging, a significantly lower number of species was measured inside the mussel beds in dredged areas compared to control and boundary areas. This effect lasted for at least 40 days. The analysis of the species composition showed that the dredged area had a significantly lower density, particularly of polychaetes compared to the boundary area. An increased number of species was recorded outside the mussel beds just after dredging, but this effect lasted for less than 7 days. After dredging, brown shrimps, C. crangon invaded the dredged areas. This species is an important predator of smaller invertebrates, and it is suspected that it was feeding on small vulnerable polychaetes exposed at the sediment surface after dredging. The dredging process was observed to form 2–5-cm deep furrows in the seabed, but the sediment texture and the organic content of the sediment was not affected. The biomass accumulation of individual blue mussels was significantly lower in the dredged area compared to the boundary area. This indicates that the disturbance of the mussel bed structure reduced growth and that the lowering of intraspecific food competition caused by a reduced density of mussels did not increase the accumulation of biomass in the mussels which remained in the dredged area.     

Surface-enhanced laser desorption/ionization-time of flight-mass spectrometry approach to biomarker discovery in blue mussels (Mytilus edulis) exposed to polyaromatic hydrocarbons and heavy metals under field conditions

Proteomics provide potential in the discovery of new sensitive biomarkers for environmental pollution. To evaluate this potential, we have utilized ProteinChip® technology to analyze the proteomic profile of blue mussels (Mytilus edulis) from polluted marine habitats surrounding the island of Karmøy, Norway. Two different types of contamination, heavy metals and polyaromatic hydrocarbons (PAHs), were compared to a clean reference site. Differentially expressed proteins/peptides were found, which showed a specific induction or a general suppression associated with the field site of origin. By combining sets of protein markers in a tree-building algorithm, we were able to correctly classify samples from these sites with an accuracy of 90%.     

Electrophoretic investigation of systematic relationships in the marine mussels Modiolus modiolus L., Mytilus edulis L., and Mytilus galloprovincialis Lmk. (Mytilidae; Mollusca)

Genetic variation was assayed electrophoretically at 13–16 loci in Modiolus modiolus, Mytilus edulis, and Mytilus galloprovincialis. High genetic distance ( D ) values were observed between Modiolus modiolus and Mytilus edulis (1.516 ± 0.523) and between Modiolus modiolus and Mytilus galloprovincialis (1.564 ± 0.539), whereas the distance between Mytilus edulis and M. galloprovincialis (0.167 ± 0.118) was rather low. The systematic status ot Mytilus edulis and M. galloprovincialis is discussed in relation to these lindings and the genetic distance values are used to estimate divergence times which in turn are compared with paleontological estimates. The observations of high average heterozygosity in Modiolus modiolus, and high correlations of locus heterozygosity between taxa are discussed briefly.     

Bioinvasion threatens the genetic integrity of native diversity and a natural hybrid zone: smooth‐shelled blue mussels (Mytilus spp.) in the Strait of Magellan

Smooth‐shelled blue mussels of the Mytilus edulis species complex are widely distributed bivalve molluscs whose introductions threaten native marine biodiversity (non‐indigenous species – NIS). The aim of the present study was to identify the species and hybrids of Mytilus present in the Magellan Region (southern Chile). Results indicate that three mussel species of the Mytilus edulis complex are found in the region – M. edulis, M. chilensis (or the Southern Hemisphere lineage of Mytilus galloprovincialis), and M. galloprovincialis of Northern Hemisphere origin. For the first time, alleles of the introduced M. trossulus are reported from the Southern Hemisphere. In the Strait of Magellan the native Pacific blue mussel, Mytilus chilensis and the native Atlantic blue mussel, Mytilus edulis, meet and mix at a natural hybrid zone (about 125 km in length). This is the first record of a natural Mytilus hybrid zone in the Southern Hemisphere and is also the first record of the co‐occurrence of genes from all four Mytilus species in any one region. These results contribute to the knowledge of the biodiversity and delimitation of mussel species in southern South America, and highlight how introduced species may threaten the genetic integrity of native species through hybridization and introgression.     

Documentation of sites of intertidal blue mussel (Mytilus edulis L.) beds of the Lower Saxonian Wadden Sea, southern North Sea (as of 2003) and the role of their structure for spatfall settlement

Field surveys (dating back to 1950) and aerial photograph series (dating back to 1966) were evaluated to determine sites of intertidal blue mussel (Mytilus edulis) beds at the Wadden Sea coast of Lower Saxony. Maps were prepared indicating sites of blue mussel beds during the last decades. A table gives additional information on the presence (or absence) of blue mussel beds at each site at the time of large-scale surveys. Altogether 187 sites of M. edulis beds were recorded in the investigation area. In spring 1996, there were still only 19 sites where mussel beds still occurred, although at 51 sites residual mussel-bed structures were present, e.g. shell bases of former beds or protruding patches (which had been occupied by M. edulis before the beds vanished) and open spaces. At that time, the majority of the sites contained neither mussel beds nor mussel-bed structures. The analysis of recent data confirmed that mussel larvae have preferred to settle in sites of present mussel beds and sites with bases of former mussel beds. There was no preferential selection of one of these categories (settled beds vs. shell bases). On the other hand, the presence of mussel beds or mussel bed structures is not obligatory for settlement, because sites without those structures were also re-settled by the spatfall in 1996, even though on a smaller scale.     

Impact of suspended mussels (Mytilus edulis L.) on plankton communities in a Magdalen Islands lagoon (Québec, Canada): A mesocosm approach

The Grande-Entrée Lagoon (Magdalen Islands, Canada) has supported mussel (Mytilus edulis) cultivation for the last 25 years. Algal biomass in this lagoon is relatively low while heterotrophic plankton biomass is high. Although often considered herbivorous, it is known that filter-feeding bivalves can consume various types of food, from bacteria to zooplankton. We hypothesize that along with phytoplankton, heterotrophs constitute an important food resource for the Grande-Entrée mussels. In situ mesocosm experiments were undertaken at different seasons using short socks filled with mussels from the same cohort taken from an aquaculture farm, in order to determine the impact of cultured mussels on local plankton communities and assess the role of heterotrophs. Filtration activity by the mussels and associated epibionts present in the socks was expressed as clearance rates (CR). The average CR over all taxa was lowest in June and highest in October. Diatoms, dinoflagellates and heterotrophic protists constituted the bulk of planktonic carbon removed by mussels. While smaller-sized taxa contributed little (< 5%) to mussel carbon intake, large-sized heterotrophs (namely ciliates) contributed 69 to 88%. Taxon-marker pigment analyses generally confirmed these observations for groups containing phototrophic pigments. The high heterotrophic biomass retained by mussels indicates they are a major food source for mussels in this environment and should be considered both in the evaluation of mussel feeding and in assessing the influence of cultured mussels on local plankton ecosystems.     

Growth development of a balsam fir (Abies balsamea (L.) Mill.) originating from layering

After a disturbance, balsam fir stands (Abies balsamea (L.) Mill.) regenerate primarily by seedlings, but layering is also known to occur and to contribute to the subsequent population base. We examined in detail the lower part of one balsam fir stem, stump and roots in order to: reconstruct the establishment of one mature balsam fir with evidence of layer-origin. The life history of this tree was then reconstructed by measuring tree-ring widths, dating all the sections, and by identifying the presence or absence of pith to differentiate between stem and root structures. We located a pith structure in this tree 51 cm below ground level. This lowest section with pith was characterized by a diameter of only 3 mm and contained 40 concentric tree-rings, suggesting that it originated from a branch. Radial and height growth measured were small until the beginning of 1930s. This period was abruptly followed by an increase in growth in both height and diameter as well as a massive production of adventitious roots, probably produced by partial harvesting of the parent tree/stand.     

Assessment of a glutathione S-transferase and related proteins in the gill and digestive gland of Mytilus edulis (L.), as potential organic pollution biomarkers

The response of the glutathione S-transferase (GST, EC 2.5.1.18) and related proteins of Mytilus edulis to environmental pollution load was assessed. Mussels were reciprocally transplanted between an industrial estuary (Douglas), a rural estuary (Youghal) and a m arine site (Bantry). In addition, m ussels were sam pled along a pollution gradient in an estuary receiving leather tannery effluent (Colligan). These latter m ussels were previously shown to be subject to oxidative stress resulting from the discharges. GST specific activity of cytosolic extracts from the gill and digestive gland tissues was determ ined for all anim als. Specific activity was shown to vary significantly in anim als from different sites, with highest specific activity always observed in sam ples (local and transplanted) taken from the industrial site. By com parison, the m ussels exposed to tannery discharges displayed no significant alteration in GST specific activity. Total intracellular glutathione (GSH) was also determ ined for sam ples taken from the Douglas and Youghal estuaries but no correlation with pollution load was observed. Using FPLC analysis, we observed no specific effect on the relative levels of the GST and the individual GST related proteins in gill or digestive gland sam ples from local or reciprocally transplanted anim als from Douglas or Youghal. The increase in GST specific activity observed in samples from the industrial estuary are indicative of a possible, specific inductive agent at this site. The results from the tannery site, by com parison, indicate that general oxidative stress does not result in elevated G ST specific activity in M. edulis.     

A first-generation genetic linkage map of the European flat oyster Ostrea edulis (L.) based on AFLP and microsatellite markers

This study presents the first genetic linkage map for the European flat oyster Ostrea edulis . Two hundred and forty-six AFLP and 20 microsatellite markers were genotyped in a three-generation pedigree comprising two grandparents, two parents and 92 progeny. Chi-square goodness-of-fit tests revealed high segregation distortion, which was significant for 32.8% of markers. Sixteen microsatellites and 235 AFLPs (170 type 1:1 AFLPs and 65 type 3:1 AFLPs) were used to build sex-specific linkage maps using crimap software. The first parental map (P₁) consisted of 104 markers grouped in nine linkage groups, and spanned 471.2 cM with an average spacing of 4.86 cM. The second parental map (P₂) consisted of 117 markers grouped in 10 linkage groups (which equals the haploid chromosome number), and covered 450.0 cM with an average spacing of 4.21 cM. The estimated coverage of the genome was 82.4% for the P₁ map and 84.2% for the P₂ map. Eight linkage groups that were probably homologous between the two parents contained the same microsatellites and 3:1 AFLPs (segregating through both parents). Distorted markers were not randomly distributed across the genome and tended to cluster in a few linkage groups. Sex-specific differences in recombination rates were evident. This first-generation genetic linkage map for O. edulis represents a major step towards the mapping of QTL such as resistance to bonamiasis, a parasitosis that has drastically decreased populations of flat oysters since the 1960s.     

Effect of male and female multiple mating on the fecundity, fertility, and longevity of diamondback moth, Plutella xylostella (L.)

Abstract:  The effect of diamondback moth (DBM), Plutella xylostella (Lep., Plutellidae) male and female multiple mating on fecundity, fertility, and longevity was studied. Males could mate for five times with virgin females during scotophase. The successful copulation rates, fecundity of female, and longevity of both females and males decreased when male mating times increased, whereas copulation duration increased. Correlation coefficient between copulation duration and male mating times was significant ( r  = 0.7358, P = 0.0001, spearman rank-order correlation). There were linear relationships between mating history of males and longevities of males and females, and regression relationships between them were significant. Mated females had similar daily reproductive pattern, which laid the most eggs on the first day after mating in spite of their mates' mating history. Virgin females laid some infertile eggs before they died. Most of the females mated once during their lifespan but 19.9% of females mated twice when one female kept with one male during scotophase. There were no significant differences in the fecundity, fertility and longevity between the single- and twice-mated females. Correlation coefficient between copulation duration and female mating times was not significant ( r  = 0.0860, P = 0.8575). Results suggested that DBM females may be monandrous. Multiple mating did not increase male or female mating fitness.