Common Mussels Research Articles

Rare earth element bioaccumulation and cerium anomalies in biota from the Eastern Canadian subarctic (Nunavik)

Recent increases in the demand for rare earth elements (REE) have contributed to various countries' interest in exploration of their REE deposits, including within Canada. Current limited knowledge of REE distribution in undisturbed subarctic environments and their bioaccumulation within northern species is addressed through a collaborative community-based environmental monitoring program in Nunavik (Quebec, Canada). This study provides background REE values (lanthanides + yttrium) and investigates REE anomalies (i.e., deviations from standard pattern) across terrestrial, freshwater, and marine ecosystems in an area where a REE mining project is in development. Results are characteristic of a biodilution of REE, with the highest mean total REE concentrations (ΣREE) reported in sediments (102 nmol/g) and low trophic level organisms (i.e., biofilm, macroalgae, macroinvertebrates, common mussels, and reindeer lichens; 101–102 nmol/g), and the lowest mean concentrations in higher-level consumers (i.e., goose, ptarmigan, char, whitefish, cod, sculpin and seal; 10−2 - 101 nmol/g). The animal tissues are of importance to northern villages and analyses demonstrate a species-specific bioaccumulation of REE, with mean concentrations up to 40 times greater in liver compared to muscle, with bones and kidneys presenting intermediate concentrations and the lowest in blubber. Further, a tissue-specific fractionation was presented, with significant light REE (LREE) enrichment compared to heavy REE (HREE) in consumer livers (LREE/HREE ≅ 101) and the most pronounced negative cerium (Ce) anomalies (<0.80) in liver and bones of fish species. These fractionation patterns, along with novel negative relationships presented between fish size (length, mass) and Ce anomalies suggest metabolic, ecological, and/or environmental influences on REE bioaccumulation and distribution within biota. Background concentration data will be useful in the establishment of REE guidelines; and the trends discussed support the use of Ce anomalies as biomarkers for REE processing in animal species, which requires further investigation to better understand their controlling factors.

Targeted metabolomics characterizes metabolite occurrence and variability in stable freshwater mussel populations.

Freshwater mussels (order Unionida) play a key role in freshwater systems as ecosystem engineers and indicators of aquatic ecosystem health. The fauna is globally imperilled due to a diversity of suspected factors; however, causes for many population declines and mortality events remain unconfirmed due partly to limited health assessment tools. Mussel-monitoring activities often rely on population-level measurements, such as abundance and age structure, which reflect delayed responses to environmental conditions. Measures of organismal health would enable preemptive detection of declining condition before population-level effects manifest. Metabolomic analysis can identify shifts in biochemical pathways in response to stressors and changing environmental conditions; however, interpretation of the results requires information on inherent variability of metabolite concentrations in mussel populations. We targeted metabolites in the haemolymph of two common mussels, Lampsilis cardium and Lampsilis siliquoidea, from three Indiana streams (USA) using ultra-high-performance liquid chromatography combined with quadrupole time-of-flight mass spectroscopy. The influence of species, stream and sex on metabolite variability was examined with distance-based redundancy analysis. Metabolite variability was most influenced by species, followed by site and sex. Inter- and intraspecies metabolite variability among sexes was less distinct than differences among locations. We further categorized metabolites by occurrence and variability in mussel populations. Metabolites with high occurrence (Categories 1 and 2) included those indicative of energy status (catabolism versus anabolism; arginine, proline, carnitine, nicotinic acid, pantothenic acid), oxidative stress (proline, glutamine, glutamate) and protein metabolism (thymidine, cytidine, inosine). Metabolites with lower occurrence (Category 3) are constituents of assorted metabolic pathways and can be important biomarkers with additional temporal sampling to characterize their variability. These data provide a reference for future temporal (before/after) monitoring and for studies of stressor-metabolite linkages in freshwater mussels.

Universal primers screening and verification for environmental DNA metabarcoding of freshwater mussels in the Lake Poyang Basin

环境DNA技术是一种非侵入、高灵敏、高效率且对环境无破坏性，对生物体无损伤的调查工具.为了筛选适合于蚌类环境DNA生物多样性研究的宏条形码引物，本研究通过对鄱阳湖流域24种常见蚌的基因组DNA进行普通扩增和高通量测序筛选了11对引物（设计了9对通用引物及从相关文献中引用了2对引物），结果显示引物cyt b和16S rRNA具有良好的扩增效果和高辨别度.进一步用环境样本（n=6）并结合传统采样技术对这2对引物进行验证，结果表明：使用引物16S rRNA共注释到蚌科物种6属8种，蚌科物种序列占总序列数的26.69%；而使用引物cyt b共注释到蚌科物种4属6种，蚌科物种序列占总序列数的6.60%.引物16S rRNA更适合用于蚌类环境DNA生物多样性研究的宏条形码引物.在生物多样性监测中环境DNA技术可以作为传统方法的有效补充，且同时使用多对引物，可增加可信度和检测率.;Environmental DNA (eDNA) technology is a non-invasive, highly sensitive, efficient and non-destructive to the environment, no damage to the organism investigation tool. To select suitable metabarcoding primers for freshwater mussel's environmental DNA biodiversity research, 11 pairs of primers (with 9 pairs of universal primers designed and 2 pairs cited from relevant literature) were screened by general amplification and high-throughput sequencing of genomic DNA of 24 common mussels in the Lake Poyang Basin. The results showed that the primer cyt b and 16S rRNA had good amplification effect and high discrimination. The two pairs of primers were further verified with environmental samples (n=6) and traditional sampling. It was found that 8 mussels species belonging to 6 genera were annotated by 16S rRNA which accounted for 26.69% of the total sequences, and 5 mussels species belonging to 4 genera were annotated by cyt b which accounted for 6.60% of the total sequences. The primer 16S rRNA was more suitable used for metabarcoding primer for the research of environmental DNA biodiversity in freshwater mussels. Environmental DNA technology can be used as an effective supplement to traditional methods in biodiversity monitoring. The reliability and detection rate can be increased by using multiple pairs of primers at the same time.

Environmental exposure of freshwater mussels to contaminants of emerging concern: Implications for species conservation

Contaminants of emerging concern (CECs) are prevalent in aquatic landscapes and may be a factor in population declines of aquatic and terrestrial fauna. Yet, there are limited data to assess the impacts of CECs to species. Understanding CEC impacts is particularly important for imperiled freshwater mussels which provide valuable ecosystem services. CEC exposure of freshwater mussels was characterized by evaluating sites with and without the federally endangered mussel (Villosa fabalis) in three subwatersheds of the Maumee River, Ohio, USA, a tributary of the Great Lakes Basin. Analyses of water, sediment, and tissue concentrations of two common mussels (Eurynia dilatata and Lampsilis cardium) indicated different CEC exposures across all 6 sites. Distinct CEC signatures were found across the three media types suggesting as mussels interact with water and sediment they may be experiencing different exposure concentrations and mixtures of CECs at different life stages. Of the 83 CECs which were detected, agricultural CECs dominated sediments, pharmaceuticals were common in tissues and water, and 16 of the 83 CECs were found co-occurring in mussel tissue, water, and sediment. There were no species differences in the CEC signatures indicating all mussels, including species of concern, may be experiencing similar exposure. Comparisons to known CEC standards indicate some exceedances in the Maumee watershed including locations of federally listed mussel species. This study provides evidence of the complexity of CEC mixes in a Great Lakes watershed and the need to understand how CECs impact declining aquatic fauna.

Dinophysis acuta in Scottish Coastal Waters and Its Influence on Diarrhetic Shellfish Toxin Profiles.

Diarrhetic shellfish toxins produced by the dinoflagellate genus Dinophysis are a major problem for the shellfish industry worldwide. Separate species of the genus have been associated with the production of different analogues of the okadaic acid group of toxins. To evaluate the spatial and temporal variability of Dinophysis species and toxins in the important shellfish-harvesting region of the Scottish west coast, we analysed data collected from 1996 to 2017 in two contrasting locations: Loch Ewe and the Clyde Sea. Seasonal studies were also undertaken, in Loch Ewe in both 2001 and 2002, and in the Clyde in 2015. Dinophysis acuminata was present throughout the growing season during every year of the study, with blooms typically occurring between May and September at both locations. The appearance of D. acuta was interannually sporadic and, when present, was most abundant in the late summer and autumn. The Clyde field study in 2015 indicated the importance of a temperature front in the formation of a D. acuta bloom. A shift in toxin profiles of common mussels (Mytilus edulis) tested during regulatory monitoring was evident, with a proportional decrease in okadaic acid (OA) and dinophysistoxin-1 (DTX1) and an increase in dinophysistoxin-2 (DTX2) occurring when D. acuta became dominant. Routine enumeration of Dinophysis to species level could provide early warning of potential contamination of shellfish with DTX2 and thus determine the choice of the most suitable kit for effective end-product testing.

Development and Single-Laboratory Validation of a Liquid Chromatography Tandem Mass Spectrometry Method for Quantitation of Tetrodotoxin in Mussels and Oysters.

In recent years, evidence has grown for the presence of tetrodotoxin (TTX) in bivalve mollusks, leading to the potential for consumers of contaminated products to be affected by Tetrodotoxin Shellfish Poisoning (TSP). A single-laboratory validation was conducted for the hydrophilic interaction LC (HILIC) tandem MS (MS/MS) analysis of TTX in common mussels and Pacific oysters-the bivalve species that have been found to contain TTXs in the United Kingdom in recent years. The method consists of a single-step dispersive extraction in 1% acetic acid, followed by a carbon SPE cleanup step before dilution and instrumental analysis. The full method was developed as a rapid tool for the quantitation of TTX, as well as for the associated analogs 4-epi-TTX; 5,6,11-trideoxy TTX; 11-nor TTX-6-ol; 5-deoxy TTX; and 4,9-anhydro TTX. The method can also be run as the acquisition of TTX together with paralytic shellfish toxins. Results demonstrated acceptable method performance characteristics for specificity, linearity, recovery, ruggedness, repeatability, matrix variability, and within-laboratory reproducibility for the analysis of TTX. The LOD and LOQ were fit-for-purpose in comparison to the current action limit for TTX enforced in The Netherlands. In addition, aspects of method performance (LOD, LOQ, and within-laboratory reproducibility) were found to be satisfactory for three other TTX analogs (11-nor TTX-6-ol, 5-deoxy TTX, and 4,9-anhydro TTX). The method was found to be practical and suitable for use in regulatory testing, providing rapid turnaround of sample analysis. Plans currently underway on a full collaborative study to validate a HILIC-MS/MS method for paralytic shellfish poisoning toxins will be extended to include TTX in order to generate international acceptance, ultimately for use as an alternative official control testing method should regulatory controls be adopted.

Detection of Tetrodotoxin Shellfish Poisoning (TSP) Toxins and Causative Factors in Bivalve Molluscs from the UK.

Tetrodotoxins (TTXs) are traditionally associated with the occurrence of tropical Pufferfish Poisoning. In recent years, however, TTXs have been identified in European bivalve mollusc shellfish, resulting in the need to assess prevalence and risk to shellfish consumers. Following the previous identification of TTXs in shellfish from southern England, this study was designed to assess the wider prevalence of TTXs in shellfish from around the coast of the UK. Samples were collected between 2014 and 2016 and subjected to analysis using HILIC-MS/MS. Results showed the continued presence of toxins in shellfish harvested along the coast of southern England, with the maximum concentration of total TTXs reaching 253 µg/kg. TTX accumulation was detected in Pacific oysters (Crassostrea gigas), native oysters (Ostrea edulis) common mussels (Mytilus edulis) and hard clams (Mercenaria mercenaria), but not found in cockles (Cerastoderma edule), razors (Ensis species) or scallops (Pecten maximus). Whilst the highest concentrations were quantified in samples harvested during the warmer summer months, TTXs were still evident during the winter. An assessment of the potential causative factors did not reveal any links with the phytoplankton species Prorocentrum cordatum, instead highlighting a greater level of risk in areas of shallow, estuarine waters with temperatures above 15 °C.

Effectiveness of a nonlethal method to quantify gamete production in freshwater mussels

AbstractStudies on the reproductive biology of freshwater mussels have contributed to conservation of this group, but methods to study early reproductive stages are either lethal (e.g., histological technique) or useful for only qualitative assessments (e.g., nonlethal syringe technique). Using 2 common mussels (Quadrula apiculata and Quadrula verrucosa) and 2 rare mussels (Quadrula petrina and Quadrula houstonensis) distributed across 3 sites in the Navasota River and San Saba River, Texas, we validated the effectiveness of the syringe technique to quantify gamete production by examining: 1) if estimates of gamete traits (sperm concentration, egg size, and egg concentration) obtained with the syringe technique were correlated to estimates of gamete traits (sperm density, egg size, and egg density) obtained with a histological technique; and 2) if survival, growth, and body condition of individual mussels sampled with the syringe technique were negatively affected in a 2-y mark–recapture field experiment....

The role of life history and behavior in explaining unionid mussel distributions

In unionid mussels, it has been proposed that opportunistic life histories are adaptive in flashy tributaries, while equilibrium life histories and thicker, sculptured shells are adaptive in higher order streams. We sampled the distributions of 9 common mussels along a gradient in stream size in southeastern Louisiana, USA, to test for life history and behavior traits as explanations of longitudinal pattern of species distributions. We found two species distribution groups, cosmopolitan species, and higher order stream specialists. Shell sectioning revealed that cosmopolitan species matured earlier, had shorter life cycles, possessed lighter shells, and grew faster. We also studied mussel movement and sediment erosion around shells in the laboratory, and our results indicated that cosmopolitan species had faster rates of movement, and were better at tracking receding water levels in the laboratory, all traits that could be adaptive in flashier headwater streams, but also suffered more scouring in a laboratory flume than species with heavier shells and sculpture. Our results verify that mussel life histories and behavior help in understanding mussel distributions in rivers, and also suggest that higher order stream species may be more at risk to disturbances like spates.

Refinement and Extension of AOAC Method 2005.06 to Include Additional Toxins in Mussels: Single-Laboratory Validation

A single-laboratory validation study was undertaken for the analysis of paralytic shellfish poisoning (PSP) toxins in common mussels, extending AOAC Official Method 2005.06 to include the additional toxins dcNEO and dcGTX2,3. The method was refined to improve toxin oxidation product stability, analytical sensitivity of N-hydroxylated toxins, and throughput. Validation was performed to characterize the method for selectivity, sensitivity, linearity, precision, repeatability, recovery, ruggedness, and uncertainty. Parallel testing of naturally contaminated mussels enabled comparison of sample toxicities obtained using mouse bioassay (MBA) and high-performance liquid chromatographic (HPLC) methodologies. Performance characteristics of the method are reported for all commercially available certified reference toxins. Results from the MBA and HPLC methods were well correlated, and the analytical method has been instigated as the sole monitoring tool for UK official control surveillance of PSP toxins in common mussels.

Retrospective monitoring of alkylphenols and alkylphenol monoethoxylates in aquatic biota from 1985 to 2001: results from the German Environmental Specimen Bank.

Breams (Abramis brama) and zebra mussels (Dreissena polymorpha) from freshwater, and common mussels (Mytilus edulis) from marine ecosystems, archived in the German Environmental Specimen Bankwere analyzed for the presence of 4-nonylphenol (NP), 4-tert-octylphenol (OP), nonylphenol monoethoxylate (NP1EO), and octylphenol monoethoxylate (OP1EO). The samples were collected in the German rivers Elbe, Rhine, and Saar, and in Lake Belau between 1992 and 2001, as well as in the North Sea and Baltic Sea between 1985 and 2001. The main purpose of the study was to investigate the effectiveness of imposed reduction measures regarding the use of alkylphenol ethoxylates. NP1EO and OP were detected in all breams. NP was predominantly above the limit of quantification (LOQ, 2 ng/g; all data on a wet weight basis), and OP1EO was mostly below the LOQ (0.2 ng/g). Maximal concentrations of 112 ng/g NP, 259 ng/g NP1EO, 5.5 ng/g OP, and 2.6 ng/g OP1EO were found in Saar breams from 1994. NP was detected in all zebra mussels from the river Elbe (up to 41 ng/g), whereas in rather few samples OP and NP1EO were found at low levels. OP1EO was not detected in any sample. Concentrations in mussels and breams from the reference site Lake Belau were below the LOQ for all compounds. In marine biota NP was found until 1997 with maximum concentrations up to 9.7 ng/g, whereas NP1EO was detected at levels between 1.7 and 12.9 ng/g in very few samples collected at the end of the 1980s. A tendency of the concentrations to decrease was obvious for all sampling sites; it was most pronounced for NP1EO and NP after 1996/1997. The effectiveness of the reduction measures is most evident at the Saar sampling site Güdingen and the North Sea sampling site Eckwarderhörne.

Retrospective monitoring of organotin compounds in marine biota from 1985 to 1999: results from the German Environmental Specimen Bank.

In archived samples from the German Environmental Specimen Bank, organotin compounds including tributyltin (TBT) and triphenyltin (TPT) as well as their degradation products were quantified. Biota samples from North Sea and Baltic Sea areas were analyzed by gas chromatography/atomic emission detection-coupling after extraction and Grignard or ethylborate derivatization. TBT and TPT were detected in nearly all samples. A decrease of TPT contamination was observed in bladder wrack, common mussels, and eelpout muscle tissues in the period 1985-1999. In this period, TPT concentrations in North Sea mussels decreased from 98 to 7 ng/g (as organotin cation concentration in wet tissue). Concentrations of TBT remained relatively constant with 17 +/- 3 ng/g for mussels from a site with nearby marine traffic and 8 +/- 2 ng/g for a more remote area. The results reflect that TBT is still used as a biocide in antifouling paints whereas the use of TPT as a co-toxicant in such preparations had been ceased in the 1980s. The fact that the use of TBT in antifouling paints was banned in 1991 for small boats within the European Community seems not to have resulted in a decrease of TBT levels in marine biota.

Cardiac and behavioural responses of mussels to risk of predation by dogwhelks

We used noninvasive, infrared phototransducers to record continuously the heartbeat of common mussels,Mytilus edulis , experiencing successive phases of interaction with the predatory gastropod Nucella lapillus, from initial threat to attack and consumption. Coupling physiological monitoring with behavioural analysis allowed us to investigate in detail the responses of mussels to predation threat. Compared to values of normal feeding activity, heart rate increased significantly when mussels were in the presence of effluent from dogwhelks. When attacked by dogwhelks, mussels increased their heart rate further, together with the rate of valve gaping. Considering the heart rate as a reliable estimator of respiratory function, these cardiac responses might be a mechanism to compensate for increased energy demand in order to cope with predation hazard. If so, the theoretical importance of trading off energy balance against risk of predation is supported by our results. Cardiac and behavioural responses varied throughout the attack according to the penetration method adopted by dogwhelks. When mussels were attacked through a drilled hole, heart rate tended to increase and periods of cardiac pausing appeared close to the point of death. In contrast, mussels attacked by penetration between the valves showed decreasing heart rate throughout the attack, together with relatively earlier cessation of valve gaping and appearance of cardiac pausing. These differences clearly support the hypothesis that dogwhelks penetrating between the valves are able to induce muscular paralysis of prey by injecting toxins.

An interlaboratory study to find an alternative to the MPN technique for enumerating Escherichia coli in shellfish

Nine laboratories in eight countries tested 16 batches of common mussels ( Mytilus edulis) over a 32 week period in order to find an alternative to the Most Probable Number (MPN) technique to enumerate E. coli. The alternatives investigated included the 3M Petrifilm system, the Merck Chromocult agar method and a Malthus conductance technique. The Petrifilm was found to be unsuitable and was subsequently dropped from the trial. After 669 analyses, a correlation of 0.83 was observed for log E. coli counts between the MPN and Chromocult methods and there was no significant evidence that either method tended to give higher readings than the other. The MPN was slightly better than the Chromocult method for repeatability but the Chromocult was slightly better for reproducibility. However, the observed differences are probably too small to be of practical importance. On the basis of these data therefore, the two methods appear equally suitable for E. coli enumeration in shellfish. There were poor correlations between these methods and the Malthus technique. A small but significant number of samples tested positive on the Malthus instrument but were recorded negative on the MPN and Chromocult tests. Subsequent analysis positively identified E. coli from these Malthus assays. After statistical analysis, errors were noted in both the MPN and Chromocult methods but it was found that there would be no statistical differences if the Chromocult agar were used as an alternative to the MPN technique.

Distribution pattern of organotin compounds at different trophic levels of aquatic ecosystems

Organotin compounds including methyl- and butyltin species were determined in selected aquatic specimens (fish muscles, fish liver, mussels, algae) as well as an sediment and water from the mud flats of the German North Sea and the River Elbe. The concentration of tributyltin (TBT) ranged between 27–202 ng/g (fresh mass) in fish muscles, 54–223 ng/g (fresh mass) in fish liver, 10–25 ng/g (fresh mass) in common mussels and 42–97 ng/g (fresh mass) in bladderwrack. The concentration of total organotin compounds (mono-, di-, and trimethyltin + mono-, di-, and tributyltin) in water samples along the River Elbe up to the Elbe estuary ranged between 30–96 ng/l. Retrospective investigation of butyltin compounds in mussel samples from the North Sea was performed by the analysis of cryogenically stored samples from 1985. A comparison of the results with that in muscles from 1993 shows that the total tin content and the TBT content decreased from 1985–1993 by a factor of 3.5 and 6.5, respectively. In addition estimated bioconcentration factors (BCF) for organotin compounds in samples from different trophic levels are presented.

Bioaccumulation of Organotin Compounds and Imposex Occurrence in a Marine Food Chain (Eastern Scheldt, The Netherlands)

During several seasons in 1995 common whelks (Buccinum undatum), mussels (Mytilus edulis) and sediment were analysed for organotin compounds. For butyltin compounds, the order of concentrations in whole body homogenate of common whelks was DBT>MBT>TBT. TBT was usually just above the detection limit except for the samples of the neural ganglia (nerve centre) taken in September. Here, only TBT could be detected, while the TBT/TPT ratio was >1. This could be important since the induction of imposex concerns the involvement of neuropeptides and/or steroid hormones. TPT concentrations in whole body homogenates of common whelks were 4–100 times higher than those of TBT. TPT clearly showed much higher levels than its metabolites DPT and MPT. No structural differences in organotin contamination were found between the sexes, different stages of imposex, or adult and juvenile common whelks. In mussels, TBT>DBT>MBT, but phenyltin ratios were comparable to those in the common whelk. Phenyltin whole body concentrations, however, were 5–10 fold below those of B. undatum. Biomagnification of butyltin compounds is not expected, whereas comparison of phenyltin ratios between the two species suggests biomagnification. In total sediment samples organotins were usually below their detection limit. The percentage of adult and juvenile female B. undatum showing imposex was > 95% throughout the year.

Environmental monitoring and banking of marine pollutants by using common mussels

Since 1985 the common mussel Mytulis edulis has been collected, characterized and stored within the framework of the German Environmental Specimen Bank program. Selected results about the determination of various pollutants such as heavy metals, polycyclic aromatic hydrocarbons and chlorinated hydrocarbons are presented. Particular emphasis is given to the comparison of seasonal variations with respect to different environmental contaminants and their correlations depending on sampling location and time.

Molecular investigations into pollutant impact on roundnose grenadier ( C. rupestris) and transplanted common mussel ( M. edulis) in Skagerrak, the North Sea

The use of a suite of different biochemical markers in the deep sea fish Roundnose grenadier and caged common mussels, and analyses of contaminant levels in the mussels, indicate that Skagerrak are more polluted than waters around the Faroe Islands. In Roundnose, induction of ethoxyresorufin- O-deethylase (EROD) is consistent with increased benzo(a)pyrene hydroxylase (BPH) in mussels and elevated levels of polynuclear aromatic hydrocarbons (PAHs) in mussels and sediment from Skagerrak. This evidence of a large-scale environmental impact of pollutants should lead to further efforts to decrease transport into, and deposition of, waste compounds in the Skagerrak area.

Radiocarbon dated common mussels Mytilus edulis from eastern Svalbard and the Holocene marine climatic optimum

Radiocarbon dated common mussels Mytilus edulis from eastern Svalbard and the Holocene marine climatic optimum

The potential role of mucus in the depuration of copper from the mussels Perna viridis (L.) and Septifer virgatus (Wiegmann)

Experiments were conducted to measure the mucus secretion rate in two common mussels in Hong Kong, Perna viridis (L.) and Septifer virgatus (Wiegmann), when chronically exposed to Cu (50 μg l −1). After a 3-month exposure period, the mucus production rate of P. viridis at 25°C in the metal treatment was 2.65 times that of the control (10.7 vs 4.0 mg g −1 dry wt h −1), while S. virgatus showed a 1.85 times difference (4.41 vs 2.38 mg g −1 dry wt h −1). Mucus secretion by P. viridis under acute Cu exposure (0.5 mg l −1) was significantly higher in the metal treatment than the control (13.43 vs 9.16 mg g −1 dry flesh wt). Metal contents of the mucus secreted was about 18 times those in the control and 6 times in the soft tissues. Therefore, mucus appears to be an effective agent for Cu depuration in the mussel. The significance of these results to the local distribution and abundance of the mussels is discussed.