The mechanism of calcium transport in mitochondria isolated from the marine mussel, Mytilus edulis (L.)

Isolated mussel mitochondria produced a less pronounced transient stimulation of respiration upon the addition of Ca²⁺ in a reaction medium containing Pi and a slower rate of Ca²⁺ transport compared to rat liver mitochondria. The initial rates of Ca²⁺ transport in the absence of Pi were more similar and both types of mitochondria possessed a sigmoidal relationship between the initial rate of Ca²⁺ transport and the free Ca²⁺ concentration $\text{(‘Km’ ? 5μM)}$. Ruthenium red produced an equal maximal inhibition of the initial rate of Ca²⁺ transport in both types of mitochondria but mussel mitochondria were rather more resistant to the inhibitor. The major difference found was that approximately 15 nmoles La³⁺ mg protein^?1 was required to produce maximal inhibition of the initial rate of Ca²⁺ transport in mussel mitochondria compared to approximately 1.0 nmole La³⁺ mg protein^?1 in rat liver mitochondria. It is concluded that mussel mitochondria possess a comparable Ca²⁺ transporter to vertebrate mitochondria and possible reasons for resistance to La³⁺ are discussed.     

Prey selection within a size-class of mussels, Mytilus edulis, by oystercatchers, Haematopus ostralegus

By comparing the shells of those mussels Mytilus edulis that had been opened by oystercatchers Haematopus ostralegus with mussels of similar size that had not been opened, it was shown that oystercatchers that break into their prey by hammering a hole in the shell selected between prey within a size-class. Ventral hammerers selected mussels that were relatively thin on the ventral surface, were brown in colour and carried few barnacles. Dorsal hammerers selected eroded mussels with thin dorsal shells. Stabbing oystercatchers did not select for thin-shelled prey. In conjunction with the great individual variation in flesh content between mussels of the same length, prey size in this case can be only a poor predictor of prey profitability.     

Putative neoplastic disorders in mussels (Mytilus edulis) from Southern Vancouver Island waters,British Columbia

Histologic examination of wild populations of Mytilus edulis in Saanich Inlet, British Columbia, Canada, revealed the presence of a highly invasive neoplasm. Two types of neoplasms were recognized; most were of hematopoietic origin, except in one mussel which had a presumptive gonadal neoplasm. Both types were apparently malignant neoplasms, based on their anaplastic appearance, invasiveness, mitotic activity, and associated tissue necrosis. This condition was observed from what is believed to be the earliest stage of the disease to the terminal stage, in which the connective tissue was almost completely replaced.     

Seasonal changes in tissue weight and biochemical composition for the bivalve Donax trunculus L. on the Algerian coast

Seasonal changes in the body weight and composition of the bivalve Donax trunculus L. from Azur Plage near Algiers, Algeria, were studied during the period September 1971-June 1974. Percentage dry tissue weight was minimal in October–December and rose to reach a peak in spring or summer, the rise corresponding with rapid maturation of the gonads. Decrease in tissue weight in the autumn also coincided with a rapid decline maturity of the gonads between August and October. Lipid content increased with sexual maturity, while carbohydrate content was greatest in the autumn and declined to a seasonal minimum in April–May. The changes are compared with those for D. trunculus in other Mediterranean populations, and for D. vittatus (da Costa) elsewhere in Europe.     

The influence of aerial exposure upon respiratory and osmotic properties of haemolymph from two intertidal mussels, Mytilus edulis L. and Modiolus modiolus L.

pH and P_O2, in Mytilus edulis L. and Modiolus modiolus L. decrease, while P_CO2 and the concentrations of Ca²⁺ and Cl^? increase during air exposure. The increase in the concentration of Ca²⁺ is 10 times greater than that of Cl^?. There is a linear correlation between the concentration of Ca²⁺ and the haemolymph P_CO2.The significance of shell valve movements and of the $\text{Ca}{}^{\mathrm{2+}}\text{H}{}^{\mathrm{+}}$ buffering by the CaCO₃ shell in response to air exposure is discussed.     

Seasonal patterns of metabolism and the heat shock response (HSR) in farmed mussels Mytilus galloprovincialis

Mussels (Mytilus galloprovincialis) are the main bivalves cultured in the Mediterranean Sea and in the Thermaikos gulf North of Greece. Global warming might affect these cultures since increases in the sea temperatures especially during summertime and may cause mass mortalities. Thus projections of the effects of global warming and the knowledge of the mechanisms of thermal limitation and adaptation are considered important in this context. In the present work we studied the seasonal expression of Hsp70 and Hsp90 of aquacultured mussels in nature in an effort to examine whether mussels are seasonally thermally stressed. Moreover we determined the activity of the key glycolytic enzyme PK in order to examine seasonal changes in the metabolic profile. The present data showed a biphasic seasonal pattern in the expression of Hsps in the mantle and PAM of M. galloprovincialis. The expression of inducible Hsp72 and Hsp90 increased between February and mid April, and remained constant or decreased slightly by the end of May. Hsps expression started again in early June leading to a gradual increase by mid July and remained by the end of August. The pattern of the HSR indicates increased protein turnover or protein damage in the tissues of aquacultured M. galloprovincialis between winter and summer seasons. The induction temperature is probably limited, and beyond some upper limits there is no further change in the HSR induction temperatures and the HSR sets in. PK activity in the mantle was significantly higher in winter than in spring. Early May saw a reactivation of PK to higher than spring values. Similar to mantle PK, PK activity in PAM was significantly higher in winter than in spring. A slight reactivation was observed by the end of August.     

Experimental test of biodeposition and ammonium excretion from blue mussels (Mytilus edulis) on eelgrass (Zostera marina) performance

Blue mussels and eelgrass have been found to coexist in many locations. However, knowledge of the interactions between these species is limited. Two experiments were conducted in the laboratory, a “Deposit” and an “Epiphyte” experiment. The Deposit experiment examined possible effects of increasing load of blue mussel (Mytilus edulis) biodeposits on sediment biogeochemistry and eelgrass (Zostera marina) performance. Z. marina mesocosms received normal or high loads of mussel biodeposits (Normal and High), while no biodeposits were added to the Control. High dosage had overall negative effects on Z. marina, which was reflected as lower leaf numbers and biomass and accumulation of elemental sulphur in rhizomes. The sediment biogeochemical conditions were altered, as the mussel biodeposits enhanced sulphate reduction rates and increased sulphide concentrations in the porewater, which may result in sulphide invasion and reduced growth of Z. marina.In the Epiphyte experiment effects of mussel excretion, with particular emphasis on ammonium, on the growth of Z. marina and their epiphytes were examined. A thick cover of epiphytes developed on Z. marina growing together with M. edulis, and the relative growth rate was reduced with 20% compared to plants from control without mussels. Overall the experiments showed negative effects on Z. marina growing together with M. edulis, thereby supporting a preceding field study by Vinther et al. [Vinther, H.F., Laursen, J.S., Holmer, M. 2008. Negative effects of blue mussel (Mytilus edulis) presence in eelgrass (Zostera marina) beds in Flensborg fjord, Denmark. Est. Coast Shelf. Sci. 77, 91-103.].     

The ecology of Mytilus edulis L. in exposed rocky intertidal communities

Information is given to show that Mytilus edulis L. is an important component of exposed rocky coast communities of the Western Hemisphere. It is abundant on the exposed coast of Washington State with a potential distribution extending from + 10.6 ft ( + 3.2 m) down to at least 10 m depth: it is not continuous along this entire gradient. It dominates a band from +10.6 ft down to +9.6 ft ( + 3.2 to + 2.9 m) tidal height where it usually intergrades with its congener M. californianus Conrad. Its upper limit appears to be determined by desiccation stress and the lower probably by competition and or predation.In the mid-intertidal zone, from + 5.6 to + 9.6 ft ( + 1.7 to 2.9 m), where M. californianus is dominant, M. edulis occurs in patches of cleared space which usually form in the M. californianus bed matrix in winter months. Here, it acts as an opportunistic species by colonizing quickly and growing rapidly to reproductive size. It is preyed upon by Thais spp. which prefer it to Mytilus californianus and eventually is eliminated from these patches. It also occurs, sometimes abundantly, in tufts of the red alga Endocladia muricata (Postels & Ruprect) J. Agardh at high and mid-intertidal heights.In low intertidal and subtidal regions, to ≈ 10 m depth, Mytulis edulis can be found in refuges of filamentous or intricately arranged substrata which generally offer protection from predation. These are represented by a wide variety of forms such as hydroids. bryozoans, filamentous algae, coralline algae, and kelp with convoluted holdfasts or complex stipes.     

Seasonal changes in the lipids of the sea anemone, Metridium senile (L.)

Total lipids were extracted from freshly collected Metridium senile (L.) in September, November, February, and June. The neutral lipid profile as well as total content was determined in each of these months. With the exception of June, the larger anemones contained less lipid as a percentage of the wet weight than did the smaller animals. In June the anemones contained the highest level of total lipid and a large part of this was sterol. In February, total lipid was also higher as a result of the increased wax ester content. Triglyceride levels remained relatively constant throughout the year while the wax ester content was found to vary both with season and temperature. Both triglyceride and wax ester levels were low in June, when sterol content was high, suggesting sexual reproduction at this time of the year. It is postulated that triglycerides serve as the primary lipid energy reserve in Metridium, while wax esters function in a secondary capacity, being called upon in times of metabolic stress such as sexual reproduction.     

Geographical variation in leucine aminopeptidase in Mytilus edulis L. From the Irish coasts

Phenotypic variation in leucine aminopeptidase has been demonstrated in Mytilus edulis L. from twelve localities in Ireland. It is proposed that one locus with three common and two rare alleles is responsible for one group of variants. The frequencies of the common alleles are significantly correlated with the relative amount of wave action (exposure) at the sites investigated. M. edulis seems to exhibit an above average amount of genetic variation thereby paralleling the variations in growth rate, shell morphology, filtration rate, and certain kinetic parameters previously recorded amongst individuals of this species. In view of the apparently close correlation between genotype and environmental conditions and since genotype in other species is known to control survival and growth rate, genetic studies of the kind described here could clearly have important implications for the commercial mussel fishery.     

A new method of monitoring ventilatory activity in mussels and its use in a study of the ventilatory patterns of Mytilus edulis L.

An apparatus for measuring pumping rates in mussels, based on the delivery of exhaled sea water into a constant flow of fresh water, is described. When food is available, pumping is continuous for several days although there are signs of satiation after ≈ 1 wk. When food is withdrawn pumping does not cease for several hours especially in animals which have been food-deprived for some time before feeding. Food-deprived mussels often fail to pump for periods of > 24 h and ventilatory bursts are carried out at flow rates well below maximum. Shell valve movements and diffusion of oxygen through the gape between open valves can supplement ciliary ventilation.     

Growth in length of Mytilus edulis L. fed on different algal diets

Mytilus edulis L. was fed on different algal diets and the increase in shell length was measured every 12–24 h. The mussels respond within 12 h to major changes in the diet. When pre-starved mussels were fed every 24 h with monocultures of Tetraselmis suecica (Kylin) Butch, there was a pronounced lag period followed by a linear increase in shell growth rate. When both pre-starved and pre-fed mussels were fed on equal rations of T. suecica with concentrations ranging from 2.5 to 10.0 × 10⁷ cells · 1^?1, the growth rate levelled off at about the same rate. Within the same range of concentrations there was a linear correlation between final growth rates and algal cell concentration. Feeding with monocultures of Isochrysis galbana (Parke) or Thalassiosira pseudonana Hasle et Heimdal (Hustedt) gave approximately the same shell growth as with Tetraselmis suecica alone, while combinations of these three algal species produced significant synergistic effects. When filtrate only from T. suecica cultures was supplied to the mussels there was a rapid initial stimulation of the shell growth. Centrifugated cells of T. suecica which were resuspended in filtered sea water, homogenized and sonicated to rupture the cells, gave 13% less growth than with untreated cells (P < 0.05). The use of the accurate laser diffraction method for length growth measurements may greatly reduce the time and effort involved in growth experiments.     

Seasonal changes in the biochemical composition of the freshwater cat-fish,Wallagonia attu (Bloch.)

Summary Seasonal changes in the various biochemical constituents of muscle, liver and gonads were studied in the cat-fish, W. attu. Distinct phases of high and low fat accumulation occurred in each tissue. Moisture in different tissues showed marked seasonal variations which were related inversely to the changes in the amount of fat. Seasonal fluctuation in protein was less pronounced in muscle and liver while in ovaries these were fairly well defined. Protein values in all the tissues were generally low during the winter. Ash content showed little variations in the three tissues. The seasonal cycles of various constituents in each tissue were correlated with the cycle of maturation and depletion of gonads. Different phases of maturation were associated with marked quantitative fluctuations of each ingredient in different tissues.     

Feeding behavior and differential absorption of biochemical components by the infaunal bivalve Mulinia edulis and the epibenthic Mytilus chilensis in response to changes in food regimes

We measured changes in the feeding rate and food absorption efficiency of two suspension feeding bivalves, cross-trasplanted between habitats with special emphasis on their capacity for differential absorption of biochemical components from their food supply. Mulinia edulis were moved from the intertidal zone to the subtidal zone, and Mytilus chilensis from the subtidal to the intertidal zone for a period of 7 days, and then compared with animal that had not been transplanted. Experimentally prepared diets similar to those available in the two different environments were offered to the bivalves, and their rates of feeding and differential uptake of biochemical components were determined and statistically compared. The two species did not achieve complete acclimation of their feeding behaviour during the transplant period since the highest ingestion rates for biochemical components occurred under dietary conditions that reflected their habitats of origin. Absorption efficiency showed greater acclimation than the other physiological parameters measured, indicating the capacity of these species to modulate their enzymatic-digestive activity depending on food composition. We conclude that both Mytilus and Mulinia have a certain degree of physiological plasticity in their feeding behaviour and assimilatory balance of biochemical components, being greater in Mytilus. When both species encounter ambient food conditions characteristic of their normal habitats, they show maximum values of food absorption, while under conditions where their typical diets are exchanged (Mytilus in intertidal and Mulinia in subtidal), the energy absorbed declines in each, but in ways very different between the two species. Thus, Mytilus exposed to high concentrations of low quality seston reduced the energy absorbed by 31.7% compared to its normal habitat, while Mulinia exposed to low concentrations of high-quality food reduced their energy absorption by 64%.     

Isolated and combined impacts of blue mussels (Mytilus edulis) and barnacles (Balanus improvisus) on structure and diversity of a fouling community

Effects of two presumably dominant competitors, the blue mussel Mytilus edulis and the barnacle Balanus improvisus on recruitment, population dynamics and community structure on hard substrata were experimentally investigated in the subtidal Kiel Fjord, Western Baltic. The hypothesis that blue mussels and/or barnacles are local dominants and strongly influence succession and community structure was tested by monitoring succession in the presence and absence of simulated predation on either or both species. Manipulations included blue mussel removal, barnacle removal, combined blue mussel and barnacle removal, as well as a control treatment for natural (non-manipulated) succession. In the second part of the experiment, recovery from the treatments was monitored over 1 year.During the manipulative phase of the experiment, blue mussels had a negative effect on recruitment of species, whereas barnacles had no significant effect. Even so, a negative synergistic effect of blue mussels and barnacles was detected. Calculation of species richness and diversity H′ (Shannon Index) showed a negative synergistic effect of blue mussels and barnacles on community structure. Additionally, diversity H′ was negatively affected by the dominant competitor M. edulis. These effects were also detectable in the ANOSIM-Analysis. The non-manipulative phase of the experiment brought about a drastic loss of diversity and species richness. Blue mussels dominated all four communities. Barnacles were the only other species still being able to coexist with mussels. Effects of simulated predation disappeared fast.Thus, in the absence of predation on blue mussels, M. edulis within a few months dominates available space, and diversity of the benthic community is low. In contrast, when mussel dominance is controlled by specific predators, more species may persist and diversity remains high.     

The kinetics of accumulation and excretion of ferric hydroxide in Mytilus edulis (I.) and its distribution in the tissues

Iron, which occurs in sea water as particulate ferric hydroxide, is accumulated to high concentrations by the common mussel, Mytilus edulis (L.). The kinetics of the accumulation and excretion of iron in Mytilus has been studied using ⁵⁹Fe-labelled ferric hydroxide and the tissue distribution and identification at the sub-cellular level determined by analytical electron microscopy. Iron-59 accumulates in linear proportion to the sea-water concentration and is found in all tissues; the concentration factors for viscera, kidneys, gills, muscle = mantle is 25: 6: 4: 1, respectively. The particulate iron is taken up by pinocytosis by special epithelial cells in the gills, gut, kidney and possibly labial palps and held in membrane-bound vesicles, unaccompanied by mucus in the case of gills and kidney, but with mucus present in the digestive diverticulum and mid-gut cells. There is no free iron within the cytoplasm. Approximately 30 % of the iron presented to the gut is not absorbed being voided with the faeces. The absorbed iron is exocytosed and then passed on to amoebocytes in the haemolymph for transport to other tissues, a major portion being excreted by transfer to the byssal threads.     

The passage of two species of micro-algae through the gut of Mytilus edulis L.

The contents of fecal ribbons from Mytilus edulis L. fed either the unicellular flagellate Tetraselmis suecica (Kylin) Butch., or the diatom Thalassiosira pseudonana (Hasle and Heimdal) were examined for their particle size spectra. Contents of fecal ribbons were dispersed by shaking in filtered sea water and analyzed by a Coulter Counter. The flagellate can pass through the mussel's gut without any significant volume changes, implying that its digestion is largely intracellular (after phagocytosis). In contrast, the diatom does undergo volume changes, probably a result of disintegration of cells and aggregation of cells and cell fragments. Undigested flagellate cells can become resuspended in significant quantities after their defecation by the mussel.     

Soluble and surface-bound aminopeptidase in eosinophilic blood cells from Mytilus edulis

This study focused on soluble and surface-bound aminopeptidase (AP) in hemocytes from Mytilus edulis and on the identification of the enzyme-producing blood cells. The cell extract hydrolyzed alanine p-nitroanilide (Ala-pNA) with an optimum between pH 6.4 and 7.0. Following native gradient PAGE of extract, alanyl methoxy-naphthylamide (AMNA) was converted by one band with an estimated molecular weight of 375 kDa; it included at least ten putative AP-isozymes with isoelectric points between pH 4.5 and 5.8. In addition to this soluble form, electron microscopy revealed simultaneous conversion of AMNA on the surface of blood cells. Individual mussels expressed AP-molecules in 23-39% of their hemocytes. These cells were shown to represent eosinophilic granulocytes.     

Hybridisations between Mytilus edulis and Mytilus galloprovincialis and performance of pure species and hybrid veliger larvae at different temperatures

The mussels Mytilus edulis L. and Mytilus galloprovincialis Lamark hybridise naturally in the wild along the Atlantic coast of Europe producing a patchwork of mixed pure species and hybrid populations. Individuals of both species were spawned in the laboratory and were hybridised in a series of reciprocal crosses. After 72 h, the proportion of eggs which developed into larvae (%yield) and the proportion of those larvae which had a normal veliger morphology (%normality) were estimated and compared between pure species and hybrid families. There were no significant differences in %yield or %normality between pure species and hybrids, but significant differences were evident between the offspring from different parents irrespective of whether they were hybrids or pure species. Therefore confirmation of hybrid heterosis in laboratory studies should not be based on a single, or a few reciprocal crosses. Hybrid and pure species veliger larvae were grown for approximately 4 weeks at 10, 14 or 20 °C. In all trials, pure M. galloprovincialis larvae grew significantly faster at 20 °C than either reciprocal hybrid or pure M. edulis larvae. Irrespective of temperature, in general, hybrid larvae grew slower than larvae of either pure species. Increased exposure to planktonic predation due to slow growth can be interpreted as selection against hybrids and this may play a role in the structure and distribution of mixed pure species and hybrid populations.     

Characterization of metal-containing granules from the kidney of the common mussel, Mytilus edulis

The metal-containing membrane-limited granules which make up some 20% of the cellular volume of the kidney cells of the marine mussel, Mytilus, have been purified and partially characterized by chemical and histochemical analysis. They contain an inorganic component (10% of their dry weight), principally iron, zinc and calcium, associated with sulphur phosphorus together with a pigmented organic component which has the histochemical and spectroscopic of lipofuschin. Microscopic and enzymic evidence indicates that the lipofuschin is present as a result of lysosomal degradation and peroxidation of cellular membranes. The granules may thus be regarded as tertiary lysosomes or residual bodies. The ash content of these lysosomes is 10-fold higher than those from mammalian sources. For this reason, Mytilus may be a useful model system for the study of intralysosomal metal accumulation.