Digestive rhythms in the mussel Mytilus edulis

Mytilus edulis L., collected from a mid-tide level on the shore, showed rhythmic changes in mantle fluid pH, crystalline style pH, style length and total protein, and in the amylase activity in the digestive gland. These changes were correlated with the changes in tidal height. Style size may be related to extracellular digestion in the stomach. Style size and amylase content of the style were not significantly correlated with each other. The changes in amylase activity in the digestive gland confirmed the existence of a tidal rhythm for intracellular digestion in M. edulis.     

ATP content and adenylate energy charge of the mussel Mytilus edulis during the annual reproductive cycle in Lindåspollene,Western Norway

The oxygen consumption rates ( VO₂) of 6 specimens (6 to 13 kg) of the albacore tuna Thunnus alalunga were measured at sea, using specimens collected 300 km west of San Diego, California (USA) during July and August, 1981. Fish were tested in a closed continuous-flow respirometer, where they swam at about 1.3 body lengths s^-1 velocity in 15° to 19°C water. The albacore tuna is a temperate pelagic species experiencing water temperatures from about 10° to 20°C and attaining a maximum weight of 45 kg. The VO₂ ranged from 1 249 to 3 336 ml h^-1 (the mean VO₂ for the 6 fish was 2 228 ml h^-1); such values approach those of mammals of a similar size and are 3 to 4 times those of most active fishes (e.g. sockeye salmon). Among fishes, the only higher VO₂ values yet recorded were for the skipjack tuna Katsuwonus pelamis, a tropical species. The remarkably high metabolic rates of tunas are presumably correlated with their continuous swimming activity and the maintenance of endothermy. The exponent relating VO₂ to body weight (1.18), although large, is not statistically different from the exponents for most other active vertebrates.     

Copper-induced differential mortality in the mussel Mytilus edulis

Copper toxicity experiments were performed with 3 000 mussels (Mytilus edulis L.) from a population that is a mixture of individuals originating in the Kattegat and in the Baltic. Subsequently, the electrophoretic patterns of the enzymes phosphoglucose isomerase (PGI) and phosphogluco mutase (PGM) were analysed in the dead and surviving mussels in order to detect possible differential mortality. Significant differences in allele frequencies between dead and surviving mussels were found for PGI. The results are discussed in relation to genotypic differences in the PGI and in relation to the composite structure of the investigated population. It is concluded that the differential mortality is due to genotypic differences in the PGI locus and/or to different susceptibility to copper by mussels originating in the two geographic areas.     

Accumulation of cadmium and bioenergetics in the mussel Mytilus edulis

Accumulation rates of cadmium, the amount of food ingested and assimilated, the amount of oxygen consumed and changes in dry flesh weight have been measured in Mytilus edulis L. exposed to 0, 10 and 100 ppb cadmium for 17 d in aquaria with seawater flowing continously and at constant algal concentration. The accumulation rates were linear at 10 and 100 ppb, amounting to 0.58 and 8.89 ppm d^-1, respectively. Body loads up to 150 ppm caused no effects on either clearance, ingestion, assimilation, respiration, or growth. High net growth efficiencies between 55–59% were obtained, indicating near optimal experimental conditions. It is suggested that the setup and experimental procedure provide an excellent tool in the study of accumulation and sublethal effects of environmental pollutants in suspension feeding bivalves.     

Hydrocarbon uptake and loss by the mussel Mytilus edulis

The dynamics of accumulation and elimination of hydrocarbons by the blue mussel Mytilus edulis were studied in a continuous-flow system. Mussels were exposed for as long as 41 days to 200 – 400 g/l of diesel fuel adsorbed on kaolin particles. Hydrocarbons were accumulated in the tissues in excess of 1000 times the exposure levels. Upon termination of dosing, the mussels exhibited a rather rapid loss of hydrocarbons for the first 15 to 20 days (biological half-life=2.7 to 3.5 days). Subsequently, however, elimination was reduced to a minimum and a considerable fraction of the hydrocarbons could be recovered from the tissues after as long as 32 days of depuration. The mussels exhibited definite signs of physiological stress due to chronic exposure to diesel fuel, although recovery was rapid upon termination of dosing. It is concluded that mussels could be utilized as a test organism for monitoring long-term hydrocarbon pollution in marine waters. The implications for the mussel culture industry are discussed.     

Quantitative studies on gonad cycle,fecundity, reproductive output and recruitment in a baltic Mytilus edulis population

Since Mytilus edulis L. is a biomass dominant in the Baltic much interest is focused on the ecology of the species. In this paper an attempt is made to quantitatively cover the reproductive cycle of a Baltic M. edulis population in order to provide data for energy flow models and to discuss aspects of recruitment in this species. Histological preparations of gonads showed that gametogenesis started with declining temperatures in autumn and proceeded very slowly through winter. At the beginning of March when food was supplied during the spring phytoplankton bloom, rapid maturation took place. This was also revealed by an increase in meat weight of the mussels. Only one spawning period was recorded, from the middle of May until the beginning of June, due to food being strongly limited to the population during the rest of the year. The length of the larval period was estimated as being 5 to 6 wk and settlement was registered from the end of June through July. In general the large annual variations found in the Baltic with regard to temperature and food abundance give rise to a more marked annual pattern in the reproductive cycle than is encountered in other seas. Fecundity was assessed for two populations from 4-and 15-m depths from studies covering two annual cycles of the changes in the relation of shell length — meat weight. The size-related fecundity was found to be equal in both populations and related to food abundance and not to growth or age. Fecundity, expressed as weight loss at spawning, ranged from 0% in 2-mm mussels and increased from 38 to 52% in 10-to 30-mm mussels. The fecundity as percentage of biomass in full-grown Baltic M. edulis is of similar magnitude as in full-grown mussels from other areas despite the smaller size of Baltic mussels. The reproductive output for the total 160 km² research area was calculated as being 1 200 tons dry weight or 80% of the standing stock, which, due to the particular features of the Baltic M. edulis population probably represents the larger part of the total mussel production. This reproductive output, calculated as 8·10⁷ eggs·m^-2 and corresponding to 50% of the total annual zooplankton production, may thus consitute an important food source for herring larvae and carnivorous zooplankton. Recruitment was divided into two phases: (1) Recruitment of juveniles (=settlement of larvae), and (2) recruitment to breeding stock. Monitoring studies of settlement on ropes and the year round presence of high abundances of mussels <2 mm indicate that settlement is in excess of the demands for maintaining population size and that most settled mussels form a pool of competitively suppressed non-growing individuals. Not until death of an already established mussel will these become recruited to the breeding population. Thus recruitment is possible throughout the year which stabilizes the population and maintains it near the carrying capacity of the area with regard to food and space availability.     

Some relationships between growth,metabolism and food in the mussel Mytilus edulis

Measurements of ingested ration, assimilated ration and metabolic rate in Mytilus edulis L. of different sizes have been integrated to provide an estimate of energy balance, which in turn describes the physiological state of the animal. These data allow the empirical determination of growth efficiency and ration. Growth efficiency increases hyperbolically with increasing ingested ration to reach a maximum, after which efficiency decreases as ration is further increased. The optimum ration for efficient growth increases with increasing weight of the mussel; maximum growth efficiency decreases with increasing body weight.     

Ice nucleation in the blue mussel (Mytilus edulis)

The ice nucleation temperatures of different homogenised organs of the mussel Mytilus edulis L. were examined. The stomach and the hemolymph had the highest nucleation temperatures. In the homogenised stomach the nucleation temperatures were fairly constant throughout the year, whereas the nucleation temperatures of the hemolymph increased in the cold season. Bacterial growth experiments, microfiltration, and experiments using antibiotics indicated that the nucleators were not of bacterial origin. The nucleation temperatures of natural seawater were approximately −9 °C, whereas seawater made from distilled water and sea salt had nucleation temperatures of about −17 °C. The nucleation temperatures of the seawater were reduced when the seawater was filtered by the mussels. However, no clear indication that the nucleators in the stomach were obtained from the seawater was found. Stomach homogenates from mussels kept in nucleator-free water had the same supercooling points as stomach homogenates from mussels kept in natural seawater. This indicates that the nucleators in the stomach are not obtained from the seawater. The temperature and light conditions examined in the present study did not significantly influence the hemolymph ice nucleation temperatures of mussels kept in the laboratory. Received: 24 October 1996 / Accepted: 16 November 1996     

The effect of copper and zinc on the metabolism of the mussel Mytilus edulis

The effects of copper and zinc on the metabolism of the mussel Mytilus edulis (L.) and its component tissues were studied. 500 ppm copper sodium citrate inhibited oxygen consumption of the whole animal and gill tissue, but no similar effect was observed on digestive gland tissue. 500 ppm zinc sodium citrate exerted no effect upon gill or digestive gland respiration, and neither metal salt affected the respiration of homogenates of gill, digestive gland or gonad. Direct observation of gill tissues during exposure to the metals revealed that 500 ppm copper sodium citrate caused inhibition of ciliary activity; exposure of tissues to 2 ppm Cu for 24 h resulted in only partial inhibition of the cilía. It is suggested that metabolic suppression noted in whole animals and gill tissues is due to the inhibition of an energy-consuming process such as ciliary activity rather than interference with respiratory enzyme systems.     

Oogenesis in the marine mussel Mytilus edulis: an ultrastructural study

Ultrastructural changes occurring during the course of development in oocytes of Mytilus edulis are described for mussels collected at monthly intervals over a period of one year (September 1981 to October 1982) from a site in Cornwall, England. During early stages of oogenesis the oocyte is surrounded by a small number of follicle cells but, as development proceeds, the follicle cells are restricted to the stalk region which attaches the oocyte to the acinar wall. Contact between the follicle cells and the developing oocyte is maintained by means of desmosomelike gap junctions. Organelles and inclusion bodies present in the ooplasm during oogenesis include rough endoplasmic reticulum (RER), Golgi bodies, mitochondria, free ribosomes, Balbiani's vitelline body, annulate lamellae and yolk and cortical granules. The RER, in particular, varies considerably throughout the course of development. Evidence for uptake of exogenous macromolecules into oocytes by pinocytosis is presented; it occurs in the basal region of previtellogenic oocytes prior to the formation of the vittelline coat. Lipid-yolk granules invariably have mitochondria in close association and, during the winter months, develop in close proximity to small, apparently glycogen-rich vesicles possibly suggesting that conversion of glycogen to lipid takes place in developing oocytes. Oocyte degeneration was commonly observed and involves initial breakdown of the plasma membrane followed by rupture of the vitelline coat. The oocyte contents once released into the acinar lumen are resorbed by the epithelial cells of the gonoducts, which are prevalent throughout the mantle of ripe individuals.     

The combined effects of salinity and temperature on larvae of the mussel Mytilus edulis

The combined effects of salinity and temperature on survival and growth of larvae of the mussel Mytilus edulis (L.) were studied. The effects of salinity and temperature are significantly related only as the limits of tolerance of either factor are approached. Survival of larvae at salinities from 15 to 40 is uniformly good (70% or better) at temperatures from 5° to 20°C, but is reduced drastically at 25 °C, particularly at high (40) and low (20) salinities. Larval growth is rapid at a temperature of 15 °C in salinities from 25 to 35, at 20 °C in salinities from 20 to 35. Optimum growth occurs at 20 °C in salinities from 25 to 30. Growth decreases both at 25° and 10 °C; the decline is most drastic at high (40) and low (20) salinities.Part of a study completed at the Bureau of Commercial Fisheries, Biological Laboratory, Milford, Connecticut, USA, while on a UNESCO Fellowship.     

The significance of temperature,salinity and zinc as lethal factors for the mussel Mytilus edulis in a polluted estuary

Mussels, Mytilus edulis L., were subjected to high temperatures, low salinities and dissolved zinc in order to investigate possible environmental hazards of a discharge of heated effluent near Newport on the Yarra River estuary, Victoria, Australia. Exposure to zinc at 0.8 mg l^-1 for 14 d in otherwise favourable conditions significantly increased mortality resulting from subsequent exposure to temperatures between 29° to 31°C for 24 h without added zinc. Mussels collected from water of temporarily lowered salinity (8–16 S) showed significantly lower thermal resistance than controls collected from marine salinities (35 S). Mussels taken from a marine environment and exposed to 10 S died at a rate which increased with temperature. Mussels acclimated for 14 d to combinations of 10°, 16° and 22°C and 22 and 35 S, and subsequently exposed to increased zinc concentrations accumulated zinc to levels which were independent of temperature and salinity. The zinc was lethal more quickly at 22°C and 35 S than at the lower temperatures and salinities. The modes of toxic action of the salinity, zinc and temperature factors are discussed and it is argued that zinc which has been found accumulated in mussels near Newport could be reducing their resistance to raised temperatures and perhaps other stresses, probably as a result of effects on lysosomal functioning. The evidence suggests that the heated effluent will accelerate any toxic effects of zinc or low salinities which occur near Newport and so poses a hazard in winter as well as in summer.     

Relationships between seston,available food and feeding activity in the common mussel Mytilus edulis

The feeding and metabolic rates of Mytilus edulis L. of different body sizes were measured in response to changes in particle concentrations ranging from 2 to 350 mg l^-1. Rates of oxygen consumption were not significantly affected by changes in seston concentration, whereas clearance rates gradually declined with increasing particle concentration. Pseudofaeces production was initiated at relatively low seston concentrations (<5 mg l^-1). Marked seasonal changes were recorded in the composition of suspended particulates (seston) in an estuary in south-west England. Total seston was sampled at frequent intervals throughout an annual cycle and analysed in terms of: particle size-frequency distributions, total dry weight (mg l^-1), inorganic content, chlorophyll a, carbohydrate, protein and lipid. The particulate carbohydrate, protein and lipid content provided an estimate of the food content of the seston. The results are discussed in terms of the food available to a nonselective suspension feeder, such as M. edulis, during a seasonal cycle. The effect of inorganic silt in suspension was mainly to limit by dilution the amount of food material ingested rather than to reduce the amount of material filtered by the mussel. In winter, the food content of the material ingested was 5%, and this increased to 25% during the spring and summer.     

Relationship between cadmium concentrations in seawater and those in the mussel Mytilus edulis

Various forms of regression analysis are presented which show that there is a significant equilibrium relationship between total recoverable cadmium in seawater and its concentration in the mussel Mytilus edulis (P<0.001). The calculations show that the concentration of cadmium in seawater should not exceed 0.20 g l^-1 if the mussel is not to reach a cadmium concentration of 2 mg kg^-1 wet weight: a value frequently used as a food standard for human consumption. Further, when a cadmium value of 2 mg kg^-1 wet weight is reached, the concentration factor by mussels for cadmium from seawater is 9 950.     

Growth,condition and specific dynamic action in the mussel Mytilus edulis recovering from starvation

Juvenile Mytilus edulis were grown individually in plastic racks in a tidal salt marsh for 72 d in 1984, starved in the laboratory for 130 d, and then fed the alga Isochrysis galbana daily for 64 d. Oxygen consumption was measured at various times during the course of starvation and recovery. The effects of both size (tissue dry weight) and condition (tissue size relative to shell size) on the rate of oxygen consumption during the course of starvation and recovery were analyzed by multiple regression. Weight-specific preprandial rate was inversely correlated with both size and condition. Weight-specific active rate (measured shortly after feeding) was correlated with size but not condition. Relative Scope for Activity was inversely correlated with size and positively correlated with condition. Relative Specific Dynamic Action (RSDA; the integrated physiological and mechanical response to a meal) was initially correlated negatively with size and subsequently positively with condition. Glycogen content was shown to be positively correlated with condition in mussels before starvation and during recovery. During recovery, experimental mussels returned to 90% of their estimated dry weight prior to starvation, and from 53% after starvation. At weekly intervals during recovery, oxygen consumption was measured following a meal until it returned to the preprandial rate. Both pre- and postprandial volumes (l at STP) of oxygen consumed per hour ( O _2pre and O _2post , respectively) increased significantly during recovery. The postprandial rise in oxygen consumption increased significantly from 15% to 23% of O _2pre . At the end of the recovery period, RSDA [( O _2post – O _2pre )/ O _2pre ] was independent of final dry weight, but was significantly correlated with percent dry weight recovered (r ²=0.44; df=10; P<0.02). The increase in RSDA may reflect increased utilization of food and its conversion to soma during recovery from starvation, as distinct from mechanical energy expenditure (feeding activity) following a meal.     

Contribution to the ecotoxicological study of cadmium,copper and zinc in the mussel Mytilus edulis

A regulation of internal levels of some essential metals has been observed in various animals, whereas the bioaccumulation of several non-essential metals parallels their overloads in water. In the mussel Mytilus edulis L., we have attempted to determine if such a phenomenon exists by comparing the patterns of accumulation of copper and zinc vs cadmium. With this aim, mussels collected in the Bay of Bourgneuf (France) in November 1983 were exposed to these metals for 16 d. At external levels of zinc as high as 100 gl^-1, mussels were able to maintain a normal concentration in all groups of organs for 4 d. The ability of mussels to limit the bioaccumulation of copper and zinc varied from organ to organ, and decreased with higher levels of contamination and longer periods of exposure. In contrast, at the lowest experimental concentration and the lowest period of exposure, a significant increase of cadmium in mussel tissues was generally observed. Even at the highest sub-lethal doses, the levels of copper and zinc in mussel tissues were not much higher than the natural levels (contaminated:background ratios= 2.3 to 6.1), whereas the bioaccumulation of cadmium was less well restricted (contaminated:background ratios=136 to 192). The use of mussels as a bioindicator of pollution seems doubtful for essential metals, particularly as regards short-term pollution, since the levels of these trace elements in the organisms are largely independent of their concentration in the ambient seawater.     

Byssus drifting and the drifting threads of the young post-larval mussel Mytilus edulis

The long, drifting threads secreted by young post-larval mussels (Mytilus edulis L.) are simple monofilaments, distinct in form and function from the attachment byssus threads. The diameters of both thread types are in the micron or sub-micron range but, whereas the attachment threads are of restricted length and terminate in an attachment plaque, drifting threads exceed the post-larva in length by more than two orders in magnitude and are without plaques or any other structures. Transmission electron micrographs of drifting threads show no evidence of internal sub-structure. In contrast, attachment threads appear to be made up of filaments. These studies confirm that the drifting threads are highly effective in enhancing the dispersal of young mussels. The terminal sinking velocity of young drifters is typically ca. 1 mm s^-1. At this velocity the suspension range above the sea bed, assuming given values of vertical diffusivity, is estimated to be 0.5 to 5 m. Calculations of the fluid drag experienced by post-larvae in the water column show that the theoretical viscous drag force on the thread is sufficient to account for the reduced sinking rate of drifters. The calculated contribution of the thread to the total drag is approximately one order of magnitude greater than that of the post-larval body. A rapid thread-deployment strategy, shown by post-larvae which are brought into suspension, may prolong each drifting excursion and thus further enhance dispersal in turbulent marine environments.     

Patterns of mtDNA diversity in North Atlantic populations of the mussel Mytilus edulis

Patterns of (female) mitochondrial DNA diversity were investigated in the blue mussel Mytilus edulis. Mytilus edulis is a ubiquitous member of contemporary North Atlantic hard-substrate communities and well represented in studies of this region. Mytilus edulis was surveyed in North America and Europe, as well as mid-Atlantic sites in Greenland, Iceland, and the Faroe Islands. Mitochondrial DNA sequences revealed considerable population structure but no monophyly of haplotypes between any major regions. Coalescent analyses suggest that migration across the Atlantic Ocean has prominently been from North American source populations and that Greenland was colonized recently and exclusively from North America. In North America, there was support for two regional groups along the North American coastline. Surprisingly, we also found evidence of recombination between some Mytilus edulis and Mytilus galloprovincialis female mtDNA sequences, particularly in northern Europe. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. An erratum to this article can be found at     

Contribution to the ecotoxicological study of cadmium,lead, copper and zinc in the mussel Mytilus edulis

The understanding of natural fluctuations of metal concentrations in mussels used as bio-indicators is indispensable for a good assessment of the disturbances due to pollution. We have studied thoroughly the factors which condition bioaccumulation by using controlled populations of mussels, Mytilus edulis L., sampled monthly over more than two years (March 1982–May 1984) in the Bay of Bourgneuf, France. Seasonal changes in metal levels have been recognized, maximum values being observed in winter and early spring and minimum in later spring and summer. Depending on metal and size group, the ratios between these maximum and minimum values varied between 1.56 and 3.43. The fluctuations in soft-tissue weight appear to be the main explanatory factor of seasonal variations in metal concentrations in mussels. Fluctuations in metal levels related to size of mussels were observed. Except for cadmium in mussels with a mean dry weight of soft tissues >0.2 g, a slight decrease in metal concentrations was observed for growing individuals: the regression coefficient b was -0.10, -0.11, -0.13 and -0.27 for Cd, Cu, Zn and Pb, respectively. The metals examined were rather uniformly distributed among the different groups of organs (visceral mass, gills and palps, remainder) and, consequently, several analyses of metals in different organs do not provide much more information than one analysis on the whole soft tissues. It is concluded that fluctuations related to size or season are reflected by only moderate differences in the maximum and minimum concentrations of metals in the mussels, but that they are nevertheless sufficient to conceal low chronic or short-term pollution, except at those sites where the normal environmental conditions are well-documented.