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.     

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.     

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.     

Metal interaction during accumulation by the mussel Mytilus edulis planulatus

Mytilus edulis planulatus (Lamarck) were collected from Howden, South-east Tasmania in autumn 1981. Interaction effects of cadmium, copper and zinc during accumulation by mussels exposed for ten days to all three metals simultaneously were examined in a series of experiments in which each metal was tested at three concentrations. In general, interaction effects were most evident at the highest concentrations tested (20 g l^-1 Cd; 20 g l^-1 Cu; 200 g l^-1 Zn) and led to a reduction in the accumulation of cadmium and an increase in that of copper and zinc. More specifically, high levels of zinc caused a decrease in cadmium uptake and an increase in copper accumulation. The presence of copper resulted in depressed cadmium accumulation while zinc accumulation increased. Cadmium tended to enhance zinc accumulation, but copper accumulation was only affected to any great extent when zinc was also present.     

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.     

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     

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.     

Assimilation of 210Po by the mussel Mytilus edulis from the alga Isochrysis galbana

Marine invertebrates are thought to accumulate ²¹⁰Po primarily from their food. In this study, a pulse-chase methodology was used to examine the assimilation and depuration of ²¹⁰Po by Mytilus edulis from the common marine alga Isochrysis galbana. The digestion of ²¹⁰Po from I. galbana occurred via a biphasic process, characteristic of a rapid (extracellular) and slow (intracellular) digestion typical of marine bivalves. The mantle/gill and foot have no known digestive role, yet their ²¹⁰Po specific activities increased after 24 h. It is proposed that this increase in ²¹⁰Po specific activity was related to ²¹⁰Po being incorporated into these tissues from ²¹⁰Po assimilated from I. galbana during extracellular digestion. It is proposed that the linear loss of ²¹⁰Po previously accumulated by control mussels was related to the continual state of renewal and replacement of cellular proteins, with ²¹⁰Po turnover and metabolism governed by protein turnover and metabolism. M. edulis' assimilation efficiency of ²¹⁰Po from the ²¹⁰Po-labelled alga was calculated to be 17.2 ± 2.1%, and thus similar to that of Ag, Cd, Co, Se and Zn by bivalves from other marine algae species. It is proposed that the assimilation efficiency of ²¹⁰Po is a function of protein assimilation. Received: 27 August 1998 / Accepted: 3 September 1999     

Effects of salinity on the net uptake of zinc by the common mussel Mytilus edulis

The net uptake of zinc by the common mussel Mytilus edulis (L.) has been investigated under different natural and artificial salinity stresses. The effects of stable and fluctuating salinities on the uptake of zinc by the mussel are discussed in terms of three possible modes of action. Under certain highly-stressful conditions, salinity may affect the uptake of zinc by the mussel. This factor should be considered when the mussel is used as an indicator of environmental pollution by zinc in estuarine areas, or spurious conclusions may result.     

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     

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.     

Assimilation of trace elements by the mussel Mytilus edulis: effects of diatom chemical composition

Mussels have been widely used as bioindicators of coastal contamination, and recent reports have demonstrated that metals are accumulated from both the dissolved phase and from ingested food. In the winter and spring of 1995, we examined the influence of the chemical composition of food (protein content, trace element concentrations and ratios in the diatom Thalassiosira pseudomana) on the assimilation of six trace elements (Ag, Am, Cd, Co, Se and Zn) in the mussel Mytilus edulis (L.). Differences of up to 38% in diatom protein content had no major influence on the assimilation of any trace element or carbon. Protein assimilation in M. edulis examined with a ³⁵S radiotracer was also independent of protein content in the diatoms. Similarly, Se assimilation in mussels was not affected by the different Se concentrations in the diatoms. Cd assimilation increased with increasing Cd concentration, presumably due to higher desorption of Cd under acidic conditions typical of the mussel gut. Zn assimilation was inversely related to Zn concentration in the food particles, implying a partial regulation of this metal in the mussels. There was no evidence of any interaction of Cd and Zn in their assimilation by the mussels. These results suggest that mussels are highly responsive, in an element-specific way, to some components of ingested food (e.g., metal concentration), but other food components (such as the biochemical composition of the algae) have little effect on assimilation.     

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.     

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.     

Demographic and temporal structure of an allele frequency cline in the mussel Mytilus edulis

Feeding rates, patterns of prey selection, and starvation tolerance were investigated for adult males and females of the cyclopoid copepod Corycaeus anglicus collected from the waters of Friday Harbor, Washington, USA. Selection by C. anglicus was determined largely by prey body-size, but was also affected by species and developmental stage. Small developmental stages of all prey species were fed upon at relatively low rates. The small calanoid species Acartia clausii was increasingly vulnerable to predation by C. anglicus as it progressed through successive developmental stages. Larger prey species, Pseudocalanus sp. and Calanus pacificus, were more vulnerable in intermediate stages, the C3 and N6 stages, respectively. Larger and smaller prey were characteristically attacked at different sites on their bodies; however, attack sites fell within a similar range of body widths, 130 to 170 m. Males of Corycaeus anglicus killed a maximum of 1.4 prey d^-1 when feeding on the optimally-sized adult females of Acartia clausii, which are approximately equivalent to its own body length. Males fed at approximately double the rates of females. Despite its small size and apparent lack of metabolic stores, this cyclopoid is highly tolerant of starvation conditions. Median survival time without food is at least 2 wk for both males and females. In its predatory behavior, C. anglicus employs an ambush-type strategy and seems to be adapted for infrequent encounters with relatively large prey.Contribution No. 1412 from the School of Oceanography, University of Washington, Seattle     

Labial palps of the blue mussel Mytilus edulis (Bivalvia: Mytilidae)

As a basis for understanding the functions of labial palps in the blue mussel Mytilus edulis, the structure and histology of palps were studied using light and scanning electron microscopy. Mussels used in the present study were collected in August 1993 and April 1994. The palp ridged surface is characterized by the presence of a smooth but densely ciliated dorsal fold, upon which rests the corresponding demibranch ventral region. The underside of the dorsal fold and the palp ridges fuse to form vestigial ciliated tracts. The dorsal fold is capable of contraction, allowing it to cover variable amounts of the ridged surface. Two different types of mucocyte are present on the palp ridged surface: subepithelial, glandular, acid-dominant secretion mucocytes and epithelial mucocytes characterized by neutral secretions. In histological section, these mucocytes appear to be concentrated on anatomical features known to intervene in particle handling. The anatomical and histological features of the smooth surface are typical of bivalve labial palps, except that the dense ciliation of the dorsal fold begins in the dorsal region of the smooth surface, indicating the possible origin of this feature. Previous studies on M. edulis point to the palps as the probable site for both ingestion volume control and particle selection; the anatomical basis of the present study should facilitate further research on these aspects.     

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.     

Formation of metallothioneins in relation to accumulation of cadmium in the common mussel Mytilus edulis

Accumulation rates of Cd have been studied in the common mussel Mytilus edulis L. under different laboratory conditions. Semi-static and through-flow experiments were carried out at Cd concentrations of 200 ppb and 50/100 ppb in the water, respectively. A linear uptake of Cd throughout the experimental periods of 36 or 124 d was found in all experiments. The accumulation rate was 3.10 ppm d^-1 at 50 ppb in the through-flow water experiment, 4.1 ppm d^-1 in starved and 6.6 ppm d^-1 in fed mussels in the semi-static experiments with 200 ppb Cd in the water. The Cd-accumulation rate in various fractions of soft parts decreased in the order: body>mantle>muscles. Elution patterns obtained from gel-filtrations showed an increasing amount of Cd-binding proteins (metallothioneins) when the body burden of Cd increased. The Cd content in the body fraction of mussels transferred to clean water for 42 d after first being exposed to Cd during 124 d decreased from 564 ppm on a dry weight basis to 417 ppm while the fraction of Cd bound to metallothioneins rose from 22 to 78% during the same period.     

Seasonal variation in mineralization rates (C-N-P-Si) of mussel Mytilus edulis biodeposits

To determine seasonal variability in mineralization dynamics of mussel biodeposits, we applied a multiple-element approach measuring mineralization rates of carbon (C), nitrogen (N), phosphorus (P) and silicate (Si) during three periods (March, August and November). The results of this study showed that mineralization rates vary between seasons and between elements and that mineralization dynamics were influenced by both temperature and biodeposit nutrient composition. Mineralization rates were 3.2 ± 0.4 mmol C, 0.17 ± 0.04 mmol N, 0.06 ± 0.02 mmol P and 3.91 ± 3.75 mmol Si per gram biodeposit (DW) per day, which represented 24 % of the particulate organic C and 17 % of the particulate organic N in mussel biodeposits. Seasonal variability was largest for Si mineralization with 60–80-fold higher rates measured in March compared to August and November. This difference is most likely related to the difference in biodeposit nutrient composition. It was furthermore shown that the labile fraction of biodeposits became mineralized after, respectively, 18, 9 and 13 days during the experimental periods in March, August and November. This indicates that temperature enhances biodeposit decomposition with approximately 2–3 times faster turnover at a 10 °C temperature interval (Q ₁₀ ).