Individual Mussels Research Articles

Assessment of natural selection in a hybrid population of mussels: evaluation of exogenous vs endogenous selection models

We examined natural selection within a population of marine mussels, sampled in southwestern England in June 1991, containing a high frequency of hybrids between Mytilus edulis L. and M. galloprovincialis Lmk. This system is particularly tractable for the assessment of natural selection because hybridization is common and individual mussels can be aged, allowing changes in the frequency of hybrid genotypes among age classes to be determined. We show that strong viability selection occurs among hybrid genotypes which results in the virtual elimination of M. edulis–like genotypes from the population over a period of 3 years. Recombinant hybrid genotypes are intermediate in fitness, with M. edulis–like genotypes having a lower survival rate and M. galloprovincialis–like genotypes having a higher survival rate than genotypes of mixed ancestry. Since intermediate fitness for hybrid genotypes is inconsistent with endogenous selection models we conclude that the structure and position of this hybrid zone is probably generated by exogenous selection. This pattern of selection is a recurring feature of this hybrid population and likely occurs elsewhere in the hybrid zone. Selection against M. edulis–like genotypes appears to be offset by extensive immigration of larvae dispersed from pure populations of M. edulis.

Seabed drag coefficient over natural beds of horse mussels (<I>Atrina zelandica</I>)

Measurements of seabed drag coefficient, C 100 , were made under tidal currents at four sites in Mahurangi Harbour, New Zealand. At the first three sites the dominant roughness element was the pinnid bivalve, Atrina zelandica (horse mussel). At the fourth site, which was devoid of horse mussels but covered in cockle shells, patches of seaweed and crab burrows, C 100 was smallest (0.0055), but still twice as large as the value typically applied to abiotic, flat, cohesionless seabeds (0.0025). The mean drag coefficient plus-or-minus standard error at the three sites with horse mussels was: 0.0082 ± 0.0010 (site 1); 0.0096 ± 0.0009 (site 2); 0.0115 ± 0.0016 (site 3). There were no clear differences amongst sites 1, 2 and 3 in terms of the attributes of individual horse mussels (e.g. shell height, width or orientation), which could have been used to explain the ranking of the drag coefficients. There were, however, differences amongst the three sites in terms of spatial distribution of individual bivalves. The site with the highest density of horse mussels, site 1, had the lowest drag coefficient and an areal concentration (λ) of horse mussels higher than typical values cited for the critical concentration (λ c ) for the onset of skimming flow over various idealized, three-dimensional roughness elements. At sites 2 and 3, the drag coefficient was given by: Formula math. which was valid for λ < λ c , where K is von Karman's constant, k is the horse mussel height (i.e., protrusion above the seabed), m 100 and λ c 0.2. The stable eddies that are hypothesized to lodge between roughness elements at concentrations greater than λ c may influence benthic community dynamics.

Seasonal and spatial variability in growth of Mytilus edulis L. in a brackish sound: comparisons of individual mussel growth and growth of size classes

Growth of Mytilus edulis L. in a brackish Danish sound was estimated from individually measured mussels and measurements of discrete size classes. In winter, individual mussels grew faster than size classes of mussels, and in summer, the inverse situation occurred. The effect of size-specific mortality of larger mussels in winter, and smaller mussels in summer on the population dynamics is discussed. Spatial variability in growth was analysed by comparing von Bertalanffy growth rates estimated for discrete size classes of mussels at different locations in the sound. Faster growth rates were measured in the western part of the sound characterised by a higher salinity and current speed. The observations were supported by results of cage experiments with individually marked mussels.

Nonlethal Evaluation of the Physiological Health of Unionid Mussels: Methods for Biopsy and Glycogen Analysis

In long-lived unionid mussels, many short-term measures of growth are of limited value. Changes in physiological condition may be an early indication of stress, because the increased energy demand associated with stress often results in a depletion of glycogen reserves, the principal storage form of carbohydrates in unionid mussels. Our goal was to nonlethally extract tissue from freshwater mussels and then to develop a rapid and dependable method for the analysis of glycogen in the tissue extracts. A biopsy technique was developed to remove between 5 and 10 mg of foot tissue in Amblema plicata plicata. The survival rate did not differ between biopsied and non-biopsied mussels during a 581-d observation period, demonstrating that the biopsy technique will allow nonlethal evaluation of the physiological condition of individual mussels through measurement of changes in contaminant, genetic, and biochemical indicators in tissue. We also modified the standard alkaline digestion and phenol-sulfuric acid analysis of glycogen for use on the small samples of biopsied tissue and to reduce analysis time and cost. We present quality control data, including method detection limits and estimates of precision and bias. The modified analytical method is rapid and accurate and has a method detection limit of 0.014 mg glycogen. Glycogen content in the biopsied samples was well above the method detection limit; it ranged from 0.09 to 0.36 mg, indicating that the method should be applicable to native mussels.

A seasonal energy budget for zebra mussels (Dreissena polymorpha) in western Lake Erie

We constructed a balanced energy budget for zebra mussels (Dreissena polymorpha) from the western basin of Lake Erie during the active growth and reproductive season (May-October). We measured metabolic costs (oxygen consumption and ammonia excretion), body mass change, and feces production weekly and marked mussels to quantify shell growth. Costs of reproduction were measured by inducing spawning four times using serotonin and collecting gametes. After conversion to calories, all energy budget components were combined with published length-frequency distributions and mussel densities to estimate population consumption. We estimated that individual zebra mussel consumption averaged 3.16 cal ·day-1 (1 cal = 4.1868 J). Metabolic costs account for &gt;90% of energy consumption. Mussels &lt;15 mm increased in body mass whereas mussels &gt;15 mm allocated energy to reproduction in lieu of somatic growth. Our estimates of population consumption were sensitive to mussel size distribution, with the most abundant size-class responsible for the greatest proportion of population consumption. Based on published estimates for primary production in western Lake Erie, our energy budget estimated that zebra mussels (10 000 - 50 000 mussels ·m-2) potentially consume an equivalent of 10-50% of summer primary production.

Modes of Byssal Failure in Forced Detachment of Zebra Mussels

Microscopic observations of the detached byssal apparatus have confirmed that the substrate plays a direct role in determining the strength of adhesion of zebra mussels. Depending on the material, 20–95% of byssal plaques detached intact due to failure of the adhesive bond with the substrate. The forces required to remove individual mussels from plates of stainless steel, mild steel, polyvinylchloride (PVC), Teflon and concrete were measured using both a direct tensile pull-off test and a wall-jet apparatus in which mussels are swept from the substrate using a jet of water. In each case the detached mussels were subsequently dissected in order to determine the mode of failure of the byssal apparatus, i.e., thread rupture, plaque adhesive failure, and root failure. It was found that the force required to detach the mussels varied significantly among the different materials and was directly proportional to the percentage of broken byssal threads.

Detection of micronuclei in gill cells and haemocytes of mussels exposed to benzo[ a]pyrene

Mediterranean mussels were exposed to benzo[ a]pyrene for 2 days at doses which had previously caused the formation of specific adducts in gill DNA. Micronuclei and other nuclear abnormalities were detected in gill cells and haemocytes in order to ascertain the induction of cytogenetic damage in two different target cells in parallel. A number of procedural details were examined initially to improve the quality of slides obtained from mussel cells. Adequate cytological preparations were obtained when gill cells and haemocytes were suspended, respectively, in Alsever and sea water with EDTA, cytospun and fixed with absolute methanol. In the exposed mussels, micronuclei significantly increased in both the large gill cells (the main cell type) and the agranular haemocytes. Granular haemocytes, cells present in variable proportions between individual mussels, did not show cytogenetic damage except at the highest B[ a]P doses. In the same slides, steady levels of binucleated cells were detected, whereas the incidence of other nuclear abnormalities was significantly higher in the exposed compared with control mussels. Precise knowledge of the replication kinetics of gill cells and haemocytes is still lacking.

Stress proteins and condition index as biomarkers of tributyltin exposure and effect in mussels

Organotin concentrations (TBT and DBT) were determined in mussels (Mytilus edulis) collected from five sites around the island of Fyn, Denmark. The relative stress protein levels were measured in gill tissue and four condition indices (CIs) were calculated for each individual mussel. The stress-70 levels did not vary significantly between sites, whereas the chaperonin levels (stress-60) were significantly elevated in mussels from Odense Fjord (p < 0.001). The stress protein levels did not reflect the degree of TBT or ∑ TBT + DBT contamination of mussel tissues. The TBT and DBT concentrations (expressed as tin) in mussels from the five sites were in the ranges 0.15--2.17 and 0.1--4.2 μg Sn per g dry weight, respectively. The combined TBT + DBT values were in the range 0.32--4.92 μg Sn per g dry weight. None of the CIs measured differed significantly with respect to the sampling site, nor were they correlated with the relative stress protein levels. The four CIs were highly consistent within individual animals. The soft tissue dry weight/total weight -- shell weight condition index proved to be the easiest to measure. This preliminary study indicates that interpretation of stress protein biomarker responses requires further detailed elucidation before they can be usefully incorporated in routine environmental monitoring programmes

The metabolic basis of genetic differences in growth efficiency among marine animals

This paper initially reviews evidence for genetic influences upon growth efficiency. We then discuss recent advances in our understanding of the metabolic links whereby genotype affects whole-animal physiology and growth efficiency through differences in protein metabolism. Most evidently, these differences are in protein turnover, defined as the continuous breakdown and replacement of cellular proteins and which provides the flux that is necessary for metabolic regulation and adaptation. Whether comparing individuals, including associations with genetic heterozygosity, or considering the response to breeding, selection or genetic manipulation, reduced whole-body protein turnover consistently underlies lower energy expenditure and higher growth efficiencies. The present paper describes results from our recent studies that have explored the metabolic basis and functional consequences of these differences in whole-body protein turnover by comparing the component activities of specific proteolytic pathways in the mussel Mytilus edulis. Traditionally, it has been thought that requirements for biosynthesis dominate energy expenditure. Nevertheless, a large component of about 30% of the empirical costs of protein deposition cannot be attributed to known synthetic processes and it has been suggested that costs of protein turnover may contribute to the discrepancy. Findings are presented showing that separate whole-body activities of the four main lysosomal proteases were collectively associated with as much as 73% of the variation in maintenance energy expenditure observed between individual mussels. These associations were positive for cathepsin B, cathepsin D and leucine aminopeptidase ( Lap-2). Alternatively, higher whole-body activity of cathepsin L was associated with lower maintenance energy expenditure, possibly because cathepsin L was most active in the main tissue of nutrient storage, thereby mobilising energy reserves and reducing the need for protein turnover in remaining tissues. Results therefore indicate profound physiological consequences of lysosomal proteolysis under conditions of partial starvation, but which vary according to functional differences between separate proteolytic pathways. These findings establish that the relative balance between proteolytic pathways is central to our understanding of different efficiencie 12989as in energy requirements and conversion efficiency.

Variations in the Reproductive Cycle ofDreissena Polymorphain Europe, Russia, and North America

SYNOPSIS. The reproductive cycle of the zebra mussel {Dreissena polymorpha) is highly variable throughout its range in Europe, Russia2, and North America. The environmental factors influencing this variation are poorly understood, but successful reproduction is occurring in areas where it was initially believed that adult zebra mussels could not survive (i.e., southern United States). The differences in mussel reproduction occurring from site-to-site make it difficult to predict timing of specific events, such as the start of larval production, that are important in initiating containment or control procedures. For example, the amount of time required for a fertilized egg to develop into a juvenile mussel can be as short as 8 days, or as long as 240 days. Release of gametes by adults can be a highly synchronized event, focused over a 1–2 week period, or it can be completely non-synchronized, occurring throughout the year. Zebra mussels in some localities start spawning at water temperatures of 12–13°C, but do not start until water temperatures reaches 22°C at other sites. While some of this variability in reproductive behavior stems from mussel adaptation to local conditions, part is due to difficulties in sampling these events. It is difficult to determine reproductive success of a specific population because of the problems in separating locally produced larvae from larvae drifting in from other areas. Further research is needed not only on the relationship between reproduction and environment at the community level, but also on the variability in response of individual mussels.

Conversion of phenoloxidase and peroxidase indicators in individual haemocytes of Mytilus edulis specimens and isolation of phenoloxidase from haemocyte extract

Haemocytes oxidized 3-amino-9-ethylcarbazole and other peroxidase indicators such as 3,3′-diaminobenzidine·4HCl, 3,3′,5,5′ tetramethylbenzidine·2HCl and 4-chloro-1-naphthol without addition of H2O2 indicating that the reaction was possibly not caused by a peroxidase. As these chromogens were also converted by a mushroom phenoloxidase in the absence of H2O2, cell smears were incubated with known substrates of phenoloxidases. One of these, l-dopa, caused strong melanin formation in several haemocytes and the reaction could be blocked by a variety of inhibitors including KCN, NaF, 1-phenyl-2-thiourea, cysteine, glutathione, ascorbic acid and HgCl2. The enzymatic activity was isolated using a concanavalin A column and separated into two fractions with an ion-exchange cartridge. The molecular weights of the glycoproteins were estimated to be 381±13.7 kDa and 316±11.1 kDa. After isoelectric focusing of a haemocyte extract and the two ion-exchange peaks, seven enzyme bands were detected with isoelectric points between pH 5.0 and 5.5. The isolated enzyme fractions both converted 3,3′,5,5′-tetramethylbenzidine·2HCl best at pH 5–6 and l-dopa at pH 7.0 without addition of H2O2. Heat-treated cells lost their enzymatic activity; however, a group of haemocytes still bound preoxidized 3-amino-9-ethylcarbazole (= AECox). Also, some of the phenoloxidase inhibitors mentioned above blocked this non-enzymatic staining reaction. About 30–57% of haemocytes from individual mussels were AECox-positive, whereas Mytilus specimens without phenoloxidase-containing cells often occurred. Haemocytes containing this enzyme exhibited a high mobility and a large percentage of them belonged to a cytotoxic cell population.

Filtration and resuspension of particulate matter and phytoplankton on an intertidal mussel bed in the Oosterschelde estuary (SW Netherlands)

In situ measurements were carried out on an intertidal mussel bed in the Oosterschelde estuary, SW Netherlands. Exchange of suspended particulate matter and phytoplankton between the water column and the mussel bed was measured with a Benthic Ecosystem Tunnel. In situ clearance rates of the mussel bed were compared to clearance rates of individual mussels measured in a field station under ambient conditions. Concentrations of suspended particulate matter (SPM) and particulate organic carbon (POC) in the water column above the tidal flat were affected by wind-induced resuspension. Chlorophyll a concentrations were higher during flood tides than during ebb tides, and were not affected by wind-induced resuspension. Clearance rates of the mussel bed ranged from 1.3 to 7.1 m(3) m(-2) h(-1). In situ measured clearance rates generally were comparable to rates observed in measurements with individual mussels in a field station. Uptake of SPM and POC by the mussel bed was highly variable. Under calm weather conditions, uptake rates were correlated with inflow concentrations. Net uptake of phytoplankton was relatively higher than the uptake of POC, indicating that a major part of the POC was resuspended and exported from the mussel bed after filtration. In addition, wind stress induced considerable resuspension and export of SPM and POC from the mussel bed. Chlorophyll a uptake was less influenced by wind, and high rates of uptake, caused by mussel filtration, were observed. The result of filtration and resuspension processes was a net uptake by the mussel bed of particulate matter containing a relatively high proportion of phytoplankton: the mussel bed acted as a selective filter for phytoplankton. [KEYWORDS: bivalves; phytoplankton; in situ measurements; particulate matter flux; wind Benthic suspension feeders; dutch wadden sea; mytilus-edulis-l; wind-driven resuspension; san-francisco bay; tidal flat; crassostrea-virginica; suspended sediment; seasonal-variation; feeding bivalves]

95/05360 Mutagenicity of exhaust gas from incineration plants of municipal waste

Specimens of mussels (Mytilus edulis), winkles (Littorina littorea), dogwhelks (Nucella lapillus) and limpets (Patella vulgata) were collected from the north-east coast of England in 1980–1981 in order to analyse the dried whole soft tissue for zinc, copper and iron. In each case, only a narrow size range of organisms was collected from a small environmentally homogeneous site and sex was taken into account. Most of the frequency distributions of metal concentrations obtained were found to show significant positive skewness. This skewness could not be explained either by the degree of mobility or type of feeding mechanism of the organisms or by any other known parameter, e.g. size, sex, habitat variation. Some individual mussels were found to be extremely good regulators of their zinc concentrations. On the other hand, other individual mussels had the ability to accumulate unusually high levels of zinc.

Application of density gradient centrifugation for separation of eosinophilic and basophilic hemocytes from Mytilus edulis and characterization of both cell groups

Different discontinuous Percoll gradients were developed to separate native as well as alcohol- or formaldehyde fixed hemocytes of Mytilus edulis into basophilic and eosinophilic cell fractions by density gradient centrifugation. The purity of the isolated cell groups ranged from 84% to 99% and was dependent on the pretreatment of the hemocytes. The percentage of both cell types differed strongly between Mytilus specimens. Hemolymph from individual mussels (n = 56) contained 14–87% of basophils (mean ± SD = 57 ± 12.9%). Basophilic cells had a diameter of 4–14 μm, the majority measuring 9–11 μm; eosinophilic cells had a diameter of 7–19 μm, the majority being 11–13 μm. Only eosinophils bound preoxidized 3-amino-9-ethylcarbazole (AECox) and varying percentages of them possessed phenoloxidase activity. Furthermore, differing numbers of eosinophils secreted cytotoxic molecules. Cell extracts derived from isolated basophils and eosinophils exhibited reproducible differences in their protein pattern after separation in SDS-PAGE under reducing conditions.

Effects of predatory crab effluent on byssus production in mussels

This study investigated the effects of effluent of edible crab ( Cancer pagurus) on byssus production by blue mussels ( Mytilus edulis). Mussels held in the laboratory secreted more, shorter, and thicker byssus threads when placed in water in which an edible crab had been than in control seawater. The cumulative length of byssus produced by individual mussels was not affected by predatory crab effluent, but byssus volume increased by 72% in crab water compared with control seawater after a 6-h period. This difference in thread volume was still great (45%) but disappeared statistically after 22 h of exposure to crab effluent. By contrast, byssus number, length and diameter were not affected by maintaining mussels in water that had contained non-predatory, herbivorous common sea urchins ( Echinus esculentus). Blue mussels can therefore alter byssus production selectively in the presence of potential predators.

Effects of heavy metals on oxygen consumption and ammonia excretion in green-lipped mussels ( Perna viridis)

Physiological responses (oxygen consumption and ammonia excretion) of the green-lipped mussel ( Perna viridis) exposed to four concentrations of Cd (0.15, 0.32, 0.70 and 1.50 ppm) and four concentrations of Zn (0.60, 1.29, 2.79 and 6.00 ppm) were monitored for 21 days. Changes occurred in the ammonia excretion rates and O:N ratios with individual mussels experiencing different metal concentrations over time. Oxygen consumption rate decreased significantly with time for Cd-exposed individuals and also decreased significantly with the interaction between the concentration of Zn and time for Zn-exposed individuals. Although low O:N ratios (<30) were obtained in most of the treatments, no predictable correlation was found between concentrations of metals and values of O:N obtained. The value of using O:N ratio as a stress index is questioned.

Assimilation of trace elements ingested by the mussel Mytilus edulis:effects of algal food abundance

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 129:165-176 (1995) - doi:10.3354/meps129165 Assimilation of trace elements ingested by the mussel Mytilus edulis: effects of algal food abundance Wang WX, Fisher NS, Luoma SN Pulse-chase feeding and multi-labeled radiotracer techniques were employed to measure the assimilation of 6 trace elements (110mAg, 241Am, 109Cd, 57Co, 75Se and 65Zn) from ingested diatoms in the mussel Mytilus edulis feeding at different rates (0.1, 0.49 and 1.5 mg dry wt h-1). Uniformly radiolabeled diatoms Thalassiosira pseudonana were fed to mussels for 0.5 h, and the behavior of the radiotracers in individual mussels was followed for 96 h in a depuration seawater system. Assimilation efficiency (AE) of each element declined with increasing ingestion rate and increased with gut passage time. The importance of extracellular digestion relative to intracellular digestion increased with ingestion activity, which, when coupled with a decline in AE, suggested that extracellular digestion is less efficient in metal absorption. Zn assimilation was most affected by ingestion rate, suggesting that AE may play a role in the physiological regulation of this metal in M. edulis. In an experiment to simulate the effects of an acidic gut, lowered pH (5.5) enhanced the release of elements from intact diatom cells, especially at low particle concentration. These results indicate that both feeding components of the mussel (i.e. gut passage time, digestive partitioning) and metal chemistry (i.e. metal release at lowered pH within the bivalve gut) are responsible for the difference in the assimilation of trace metals at different food quantities observed in mussels. Mussels . Assimilation . Bioindicators . Metals . Americium . Cadmium . Cobalt . Selenium . Silver . Zinc Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 129. Publication date: December 14, 1995 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1995 Inter-Research.

Effects of Zebra Mussels (Dreissena polymorpha) on Bacterioplankton: Evidence for Both Size-Selective Consumption and Growth Stimulation

Zebra mussels had significant direct and possible indirect effects on heterotrophic bacteria in two contrasting sites in Saginaw Bay. At a eutrophic site in the inner portion of Saginaw Bay, mussels fed directly on bacterial-sized particles and had a negative impact on bacterial abundances. Mussels removed large bacteria (> 0.9μm) more effectively than small bacteria at this site. Individual mussels cleared from 37–89ml per day. Results using different sizes of fluorescent microspheres suggest that zebra mussels have a lower limit for particle size removal that is less than 0.4μm. Contradictory to inner bay results, mussels at an outer bay oligotrophic site had a positive impact on heterotrophic bacterial abundance, perhaps as a result of indirect effects, such as nutrient or organic carbon excretion by the mussels. Differences in the impact of mussels on the bacterial communities of the inner bay and outer bay probably result from differences in trophic state and bacterial community structure. A hypothesized smaller size of bacteria at outer bay sites may enable them to escape heavy predation pressure from mussels and the high rates of mussel nutrient excretion may facilitate their growth in these nutrient depleted conditions.

Effects of substratum instability on locomotion and pedal laceration in Metridium senile (Anthozoa:Actiniaria)

On the west coast of Sweden, populations of the small morph of the sea anemone Metridium senile (L.) are often found associated with beds of the mussel Mytilus edulis (L.). We tested the hypothesis that instability of the secondary substratum provided by mussels affects pedal disc laceration of M. senile by stimulating locomotion. The instability of a subtidal bed of M. edulis was quantified by recording movements of individual mussels. Rates of pedal disc laceration of M. senile were investigated in field and laboratory experiments using live and eviscerated mussels as substrata. Field experiments showed that M. senile produced significantly more lacerates on live mussels than on mimic (eviscerated) mussels. In a laboratory flume experiment, the rate of laceration on mimic mussels increased significantly with the frequency of substratum perturbation (overturning) with maximum laceration rates of groups overturned once every 12 and 48 h. Furthermore, the rate of laceration was found to be a function of anemone body size per se. During periods between overturning of the mimics, anemones showed a significant net migration from the protected lower shell to the exposed upper shell in pace with the frequency of overturning. The presence of a vertical flow velocity gradient between and above the mimics supported the hypothesis that migration was due to a rheotactic response in M. senile. The significance of this behavioral pattern and stimulated clonal growth in structuring populations of M. senlle on unstable substrata is discussed.

Population Dynamics of the Mussel Mytilus edulis along Environmental Gradients: Spatial Variations in Density-Dependent Mortalities

From September 1976 to September 1983, we examined how studies of the 12 individual mussel beds in the Exe estuary could enhance our understanding of the dynamics of the whole intertidal mussel Mytilus edulis L. population. The 12 beds varied considerably in their distance up-river from the estuary mouth, muddiness of their substrata and level on the shore, the three main features defining the environmental gradient for mussels in the Exe. Since adult (> 1-year old) densities over the whole estuary were already known to be strongly regulated during the first year, we focused on spat (0-year) mussels