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.     

Age-dependence of metabolism in mussels Mytilus edulis (L.) from the White Sea

Age structure, natural mortality and growth, as well as age- and size-dependent changes in parameters of energy metabolism were studied in blue mussels Mytilus edulis (L.) from the White Sea. Mussels were sampled in August (Summer sample, SS) and October (Autumn sample, AS) and contained animals of three size groups, 2-9 years old. Field data showed an increase of mortality of mussels and strong decrease in growth rates after 6 years of age. Absolute tissue growth increment (AI) reconstructed from winter growth marks on the shells decreased with age and was strongly size-dependent, while relative tissue growth increment (RI) did not depend on size of the animals. Respiration rates and citrate synthase activity demonstrated power regression versus tissue weight with regression coefficients -0.231 and -0.170, respectively. After weight correction both parameters showed a decrease with increasing age. ATP and phosphagen levels also showed a pronounced decrease in animals older than 5-6 years despite considerable differences in the absolute values of both parameters in SS and AS. pH(i) in mussels was also age-dependent and decreased with increasing age after 5 years. In air exposed mussels, pH(i) was reduced only at young age such that pH(i) was low and constant within the whole age range. Our data give evidence that aerobic metabolic rate in M. edulis from the studied population declines when animals reach an age of about 6 years. The decrease in oxygen consumption reflects the drop in mitochondrial respiration, which is mirrored by the decrease in CS activity. A concomitant fall in ATP turnover may include a downregulation of the mechanisms of acid-base regulation. pH(i) will then approach equilibrium indicated by lower pH(i) values in older animals. Our data suggest that intrapopulational comparisons of physiological parameters in mussels should take into account age composition of compared samples.     

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.     

Pollution from mining in South Greenland: uptake and release of Pb by blue mussels (Mytilus edulis L.) documented by transplantation experiments

Long-term impact of former mining activities on the marine sub-Arctic ecosystem in the Ivittuut area, Arsuk Fjord, South Greenland, was studied by transplantation experiments with the blue mussel Mytilus edulis. Measurements of metal concentration in mussels were conducted using atomic absorption spectrometry (flame AAS) and graphite furnace atomic absorption spectrometry (graphite furnace AAS). Uptake and release of Pb were documented to be slow processes. For mussels transplanted from the pristine Kugnait Bay to the polluted mining site at Ivittuut, a continuous accumulation throughout the experiments was found. Linear uptake rates of 5.86, 6.94 and 11.62 μg Pb month⁻¹ for small, medium and large mussels were found for a 6-week experiment, whereas exponential uptake rates of 0.26, 0.20 and 0.28 month⁻¹ were found for a 9-month experiment. It is estimated that the transplanted mussels will reach the same level as the resident population 12–16 months following transplantation. Mussels transplanted from the polluted mining site at Ivittuut to the pristine Kugnait Bay depurated only 7–21% of their original Pb content, and the release was within the first 10 days following transplantation, after which the Pb content remained constant.     

Carbonic anhydrase activity and biomineralization process in embryos, larvae and adult blue mussels Mytilus edulis L.

To decide whether a physiological role can be attributed to enzymatic activity with respect to crystal formation and biomineralization of the first larval shell, carbonic anhydrase (CA) activity was measured in embryos and larvae of the blue mussels Mytilus edulis L. Also, CA activity was determined in the mantle edge and gonads of adult mussels with different shell length and condition index. The intention was to find a possible correlation between CA activity and adult shell calcification, i.e. gonadal maturation. The comparison of CA activity in different developmental stages of mussels and the results of an X-ray diffraction study of biomineralization processes in embryonic and larval shells indicate that CA activity is maximal at the end of several developmental stages. Consequently, the increase in CA activity precedes some physiological changes, i.e. the somatoblast 2d formation and the occurrence of the first calcite and quartz crystals in embryos, shell field formation in the gastrula stage, shell gland and periostracum production in trochophores, and rapid aragonite deposition in larval prodissoconch I and prodissoconch II shells. Furthermore, it was found that in adult mussels CA activity was quite variable and that in the mantle edge it was frequently inversely related to the activity in the gonad. Received: 28 November 1998 / Received in revised form: 30 August 1999 / Accepted: 31 August 1999     

Fate of infectious salmon anaemia virus (ISAV) in experimentally challenged blue mussels Mytilus edulis

In order to investigate the potential role of blue mussels Mytilus edulis as a vector of the fish pathogenic infectious salmon anaemia virus (ISAV), we developed an experimental bioaccumulation system in which mussels can accumulate virus during normal filtration. Detection of virus in mussels was performed by means of real-time RT-PCR. ISAV-RNA was detected in the mussels until 72 h post-challenge. Hepatopancreas homogenate from experimentally challenged mussels was injected into salmon. All the fish injected with homogenate prepared immediately after accumulations were strongly ISAV positive 4 wk post-challenge. In the group injected with homogenate prepared 24 h after the challenge, 1 fish out of 25 was weakly ISAV positive. All of the fish that were challenged with mussel homogenate prepared 96 h after accumulation were ISAV negative. Mussels sampled from a tank with experimentally infected salmon demonstrating clinical signs consistent with ISA (infectious salmon anaemia) and mussels collected on net pen cages during ISA outbreaks in Atlantic salmon were all ISAV negative. The results indicate that the ISAV is rapidly inactivated in mussels and that mussels are not a likely reservoir host or vector for ISAV.     

A procedure for large-scale purification of domoic acid from toxic blue mussels (Mytilus edulis)

Pure domoic acid is required for use in research to investigate the biological effects of this new shellfish toxin. It may also prove to be a useful tool in studies exploring the basis of Alzheimer's disease. In this paper we describe a procedure which is effective in obtaining adequate quantities of pure domoic acid from blue mussel (Mytilus edulis). The procedure involves tissue homogenization, treatment of homogenate with chloroform and methanol, and separation of different phases with the addition of water. The aqueous-methanolic phase (upper layer) contains water soluble components including domoic acid, the chloroform phase (lower layer) contains lipoid moieties, and the interphase contains denatured proteins. The aqueous phase containing domoic acid was removed, rotory evaporated to get rid of methanol, followed by ultrafiltration to remove high molecular weight contaminants. The filtrate was lyophilized, resuspended in 1 N HCl, centrifuged and the resulting clear solution subjected to column chromatography on C18 reversed phase silica gel. Fractions containing domoic acid were pooled, and lyophilized. A brownish dry powder contained pure domoic acid with 60–65% yield from the original tissue homogenate. Another 10–15% of domoic acid was mixed with its isomer, and can be further resolved to obtain an overall recovery of 75–80% of the starting material.     

Proteome modifications of blue mussel (Mytilus edulis L.) gills as an effect of water pollution

The discharge of chemicals such as oil associated or not with derived products constitutes a real threat for the environment. We report here the differential expression of the blue mussel (Mytilus edulis) gill proteins corresponding to two contaminated environmental conditions: crude oil and offshore produced water. In order to evaluate and understand contaminants, effects and adaptive response of these organisms, we identified proteins using MS. The latter can be grouped into three main classes: proteins involved in the cellular structure, in metabolism, and in defence proteins.     

Comparative study of predatory responses in blue mussels (Mytilus edulis L.) produced in suspended long line cultures or collected from natural bottom mussel beds

Blue mussels (Mytilus edulis L.) are a valuable resource for commercial shellfish production and may also have uses as a tool in habitat improvement, because mussel beds can increase habitat diversity and complexity. A prerequisite for both commercial mussel production and habitat improvement is the availability of seed mussels collected with minimum impact on the benthic ecosystem. To examine whether mussels collected in suspended cultures can be used for bottom culture production and as tool in habitat improvement, the differences in predatory defence responses between suspended and bottom mussels exposed to the predatory shore crab (Carcinus maenas L.) were tested in laboratory experiments and in the field. Predatory defence responses (byssal attachment and aggregation) and morphological traits were tested in laboratory, while growth and mortality were examined in field experiments. Suspended mussels had an active response in relation to the predator by developing a significantly firmer attachment to the substrate and a closer aggregated structure. Bottom mussels had a passive strategy by having a thicker shell and larger relative size of the adductor muscle. In a field experiment mussels originated from suspended cultures had a higher length increment and lower mortality when compared to bottom mussels. It is concluded that suspended mussels potentially are an alternative resource to bottom culture and can be used in habitat improvement of mussel beds, but that the use of suspended mussels has to be tested further in large-scale field experiments.     

Peroxisomal proteomic approach for protein profiling in blue mussels (Mytilus edulis) exposed to crude oil

Peroxisomal proteomic protein profiles of exposure to marine pollution have been recently introduced in biomonitoring experiments. However, laboratory experiments to study the independent effect of common pollutants are needed to define a minimal protein expression signature (PES) of exposure to a specific pollutant. The aim of this study was to obtain PESs in blue mussels (Mytilus edulis) exposed to two different crude oil mixtures for future application in biomonitoring areas affected by oil spills. In the study, peroxisome-enriched fractions from digestive gland of M. edulis (L., 1758) were analysed by two-dimensional fluorescence difference electrophoresis (DIGE) and mass spectrometry (MS) after 3 weeks of exposure to crude oil mixtures: crude oil or crude oil spiked with alkylated phenols (AP) and extra polycyclic aromatic hydrocarbons (PAH) in a laboratory flow-through system. A minimal PES composed by 13 protein spots and unique PESs of exposure to the two different mixtures were identified. A total of 22 spots from the two-dimensional maps that had shown a significant increase or decrease in abundance in each of the exposed groups exposed were analysed. The hierarchical clustering analysis succeeded in discriminating the exposed groups from the control groups based on the unique PES. The PESs obtained were consistent with protein patterns obtained in previous field experiments. The results suggest that the protein profiles obtained by peroxisomal proteomics could be used to assess oil exposure in marine pollution assessments.     

Effect of nutrient supply on growth of blue mussels (Mytilus edulis) in a landlocked bay

The growth of blue mussels (Mytilus edulis) was studied in the landlocked bay Hopavågen in central Norway for 3 years, of which in 2 years (1998 and 1999) nutrients were added to increase the primary production. Nutrients (N:Si:P) were added daily from May to October in 1998 (molar ratio 15:5:4.1) and 1999 (molar ratio 16:8:1). The doses of nutrients correspond to 0.4 and 0.8 g P l^–1 day^–1 in 1998 and 1999 respectively. The growth of blue mussels (Mytilus edulis) in 1997 was followed at four depths (1, 2, 4 and 7 m). In 1998 and 1999 growth was followed at 2 and 10 m depths at four locations in Hopavågen and at a control station outside on the coast. The nutrient supply in 1998 only slightly increased the algal biomass (chlorophyll a), whereas mean daily primary production during the summer remained at the same level as the previous year. The increased nutrient supply in 1999 caused a nearly 50 and 100% increase in mean summer biomass and daily primary production, respectively. The growth of blue mussels in Hopavågen in 1997 and 1998 was within the same size range during the summer. In 1999 the shell length of blue mussels kept at 2 m depth was significantly higher than in the previous year at end of the growth season. The recorded growth was also significant higher than for mussels at 2 m depth at the control station. No difference in shell length was observed on mussels grown at 10 m depth in Hopavågen and in the control stations in 1998 and 1999. A higher tissue content was found in blue mussels grown at 2 m depth in Hopavågen, both in 1998 and 1999 when compared to the control groups. At 10 m depth no differences were recorded.     

Growth and longevity of Mytilus edulis (L.) from northeast Europe

The growth of mussels, Mytilus edulis (L.), was studied in most of the northeastern part of their distribution. The growth, longevity and maximal size of molluscs from 24 wild populations and one cultured population located in the White Sea and the southeast part of the Barents Sea were compared. The 25 studied populations were combined in six clusters. The maximal longevity and the size of the mussels varied between 7 and 18 years and 25.5 and 77.7 mm, respectively. The geographical location of the population within the studied region did not affect either maximal longevity or maximal size, or the growth rate of mussels. However, these parameters were influenced by local habitat conditions, primarily connected with the position within intertidal and subtidal zones. Animals inhabiting the intertidal zone were characterized by relatively low growth performance, a short life span and a small size. The longest life span was typical for deep subtidal mussels, whereas the highest growth rate was recorded in the cultured population and in the upper subtidal habitats. Growth patterns of Mytilus edulis in the subarctic White and the Arctic southeast Barents seas are similar to those reported from other parts of the area of distribution. Therefore, growth was mostly determined by local environmental factors, including those related to vertical zonation, rather than by latitude/longitude and related temperature effects.     

The effects of organic and inorganic pollutants on intracellular phosphate compounds in blue mussels (Mytilus edulis).

1. The effects of sublethal concentrations of organic and inorganic pollutants on intracellular energy-rich phosphates in blue mussels, Mytilus edulis, were investigated by in vivo 31P-NMR. 2. Formaldehyde (30 and 10 mg/l), phenol, pyridine, mercury and cadmium gave marked reductions in phosphoarginine and, in some cases, the ATP amounts. The reduction in high-energy phosphate was accompanied by an increase in inorganic phosphate in all groups. 3. A "phosphorus index", the product of the ratios between phosphoarginine and inorganic phosphate, and ATP and inorganic phosphate, is suggested, which might serve as an early warning ("alarm") parameter in environmental monitoring. 4. Diversity in the responses to different pollutants make phosphorus compounds in M. edulis also an interesting element in a finger print parameter system designed to distinguish between pollutants in the marine environment.     

Allometric equations for maximum filtration rate in blue mussels Mytilus edulis and importance of condition index

The relationship between body dry weight (W) and shell length (L) of blue mussels, Mytilus edulis, can be expressed by the condition index (CI = W/L ³) which varies from population to population and during the year. Here, we examine the influence of CI on the relationships between maximum filtration rate (F, l h^?1), W (g), and L (mm) as described by the equations: F _W  = aW ^b and F _L  = cL ^d , respectively. This is done by using available and new experimental laboratory data on M. edulis obtained by members of the same research team using different methods and controlled diets of cultivated algal cells. For all data, it was found that F _W  = 6.773W ^0.678 and F _L  = 0.00135L ^2.088 which are very similar to equations for mussels with ‘medium condition’ (CI = 4–6 mg cm^?3): F _W  = 6.567W ^0.681 and F _L  = 0.00150L ^2.051, with b- and d-values within a few percent of the theoretically expected of 2/3 and 2, respectively. Further, based on the present data, we propose a correction factor expressed by the empirical relation F _W /F _L  = 0.3562CI^2/3 which implies that F _W tends to underestimate the actual filtration rate (F _L ) when CI < 4.70 and to overestimate the filtration rate when CI > 4.70.     

Factors influencing bactericidal activity of blue mussel (Mytilus edulis) haemocytes against Salmonella typhimurium

This study showed that in vitro survival of Salmonella typhimurium, after exposure to haemocytes of Mytilus edulis, was significantly affected by the lipopolysaccharides (LPS) structures expressed on the cell surface of the bacteria. Survival seemed to be affected by the surrounding temperature as well. Mussel haemocytes were in vitro exposed to mutants of S. typhimurium, expressing differences in O -antigen polysaccharide chains and core sugars of LPS on their cell surface. Surviving cells of the mutants were determined after incubation with the haemocytes at different temperatures, using a colorimetric assay. In addition, a complementary study on clearance of these mutants, inoculated into the adductor muscle of mussels, was performed at 6 and 20 degrees C. It was concluded that the survival index (SI%) measured in vitro for the mutant with complete LPS was significantly lower at 6 degrees C (c.15%) compared to that at 14 and 20 degrees C (c.70%). SI% for the other mutants was c.35-45% and was not affected by temperature. The in vivo study at 20 degrees C showed that during the first 24h, the clearance rate for the mutants with complete LPS was significantly higher than for the others. Thereafter all mutants, with exception for the most deficient, started to increase in numbers and caused death to the mussels. At 6 degrees C the mutants were slowly reduced and after 17 days, viable cells of the mutant with complete LPS were still detectable in the haemolymph. The study indicated that the mussel haemocytes responded in relation to the LPS of the mutants. However, more intact LPS also seemed to protect the bacteria from being killed. The higher temperatures favoured the growth of the mutants that managed to resist the haemocyte defence. Cell surface properties and temperature seem to affect the survival of bacteria in mussels, which consequently can affect risk assessments in regard to public health.