Tissue distribution of a coliphage and Escherichia coli in mussels after contamination and depuration.

Experiments were undertaken to determine the tissue distribution of Escherichia coli and a coliphage after contamination of the common mussel (Mytilus edulis). Mussels were contaminated with high levels of feces-associated E. coli and a 22-nm icosahedral coliphage over a 2-day period in a flowing-seawater facility. After contamination, individual tissues were carefully dissected and assayed for E. coli and the coliphage. Contaminated mussels were also analyzed to determine the tissue distribution of the contaminants after 24- and 48-h depuration periods. The majority of each contaminant was located in the digestive tract (94 and 89% of E. coli and coliphage, respectively). Decreasing concentrations were found in the gills and labial palps, foot and muscles, mantle lobes, and hemolymph. Our results indicate that contamination above levels in water occurred only in the digestive tract. Contaminated mussels were depurated in a commercial-scale recirculating UV depuration system over a 48-h period. The percent reductions of E. coli occurred in the following order: digestive tract, hemolymph, foot and muscles, mantle lobes, and gills and labial palps. The percent reductions of the coliphage were different, occurring in the following order: hemolymph, foot and muscles, gills and labial palps, mantle lobes, and digestive tract. Our results clearly demonstrate that E. coli and the coliphage are differentially eliminated from the digestive tract. The two microorganisms are eliminated at similar rates from the remaining tissues. Our results also clearly show that the most significant coliphage retention after depuration for 48 h is in the digestive tract. Thus, conventional depuration practices are inappropriate for efficient virus elimination from mussels.     

Differential depuration of poliovirus, Escherichia coli, and a coliphage by the common mussel, Mytilus edulis

The elimination of sewage effluent-associated poliovirus, Escherichia coli, and a 22-nm icosahedral coliphage by the common mussel, Mytilus edulis, was studied. Both laboratory-and commercial-scale recirculating, UV depuration systems were used in this study. In the laboratory system, the logarithms of the poliovirus, E. coli, and coliphage levels were reduced by 1.86, 2.9, and 2.16, respectively, within 52 h of depuration. The relative patterns and rates of elimination of the three organisms suggest that they are eliminated from mussels by different mechanisms during depuration under suitable conditions. Poliovirus was not included in experiments undertaken in the commercial-scale depuration system. The differences in the relative rates and patterns of elimination were maintained for E. coli and coliphage in this system, with the logarithm of the E. coli levels being reduced by 3.18 and the logarithm of the coliphage levels being reduced by 0.87. The results from both depuration systems suggest that E. coli is an inappropriate indicator of the efficiency of virus elimination during depuration. The coliphage used appears to be a more representative indicator. Depuration under stressful conditions appeared to have a negligible affect on poliovirus and coliphage elimination rates from mussels. However, the rate and pattern of E. coli elimination were dramatically affected by these conditions. Therefore, monitoring E. coli counts might prove useful in ensuring that mussels are functioning well during depuration.     

Tissue distribution of a coliphage and Escherichia coli in mussels after contamination and depuration

Experiments were undertaken to determine the tissue distribution of Escherichia coli and a coliphage after contamination of the common mussel (Mytilus edulis). Mussels were contaminated with high levels of feces-associated E. coli and a 22-nm icosahedral coliphage over a 2-day period in a flowing-seawater facility. After contamination, individual tissues were carefully dissected and assayed for E. coli and the coliphage. Contaminated mussels were also analyzed to determine the tissue distribution of the contaminants after 24- and 48-h depuration periods. The majority of each contaminant was located in the digestive tract (94 and 89% of E. coli and coliphage, respectively). Decreasing concentrations were found in the gills and labial palps, foot and muscles, mantle lobes, and hemolymph. Our results indicate that contamination above levels in water occurred only in the digestive tract. Contaminated mussels were depurated in a commercial-scale recirculating UV depuration system over a 48-h period. The percent reductions of E. coli occurred in the following order: digestive tract, hemolymph, foot and muscles, mantle lobes, and gills and labial palps. The percent reductions of the coliphage were different, occurring in the following order: hemolymph, foot and muscles, gills and labial palps, mantle lobes, and digestive tract. Our results clearly demonstrate that E. coli and the coliphage are differentially eliminated from the digestive tract. The two microorganisms are eliminated at similar rates from the remaining tissues. Our results also clearly show that the most significant coliphage retention after depuration for 48 h is in the digestive tract. Thus, conventional depuration practices are inappropriate for efficient virus elimination from mussels.     

Differential depuration of poliovirus, Escherichia coli, and a coliphage by the common mussel, Mytilus edulis.

The elimination of sewage effluent-associated poliovirus, Escherichia coli, and a 22-nm icosahedral coliphage by the common mussel, Mytilus edulis, was studied. Both laboratory-and commercial-scale recirculating, UV depuration systems were used in this study. In the laboratory system, the logarithms of the poliovirus, E. coli, and coliphage levels were reduced by 1.86, 2.9, and 2.16, respectively, within 52 h of depuration. The relative patterns and rates of elimination of the three organisms suggest that they are eliminated from mussels by different mechanisms during depuration under suitable conditions. Poliovirus was not included in experiments undertaken in the commercial-scale depuration system. The differences in the relative rates and patterns of elimination were maintained for E. coli and coliphage in this system, with the logarithm of the E. coli levels being reduced by 3.18 and the logarithm of the coliphage levels being reduced by 0.87. The results from both depuration systems suggest that E. coli is an inappropriate indicator of the efficiency of virus elimination during depuration. The coliphage used appears to be a more representative indicator. Depuration under stressful conditions appeared to have a negligible affect on poliovirus and coliphage elimination rates from mussels. However, the rate and pattern of E. coli elimination were dramatically affected by these conditions. Therefore, monitoring E. coli counts might prove useful in ensuring that mussels are functioning well during depuration.     

Behavior of Escherichia coli and male-specific bacteriophage in environmentally contaminated bivalve molluscs before and after depuration.

We monitored the differential reduction rates and elimination patterns of Escherichia coli and male-specific (F+) bacteriophage during UV depuration for 48 h in oysters (Crassostrea gigas) and mussels (Mytilus edulis) contaminated by short-term (1 to 3 weeks) and long-term (more than 6 months) exposure to sewage in the marine environment. The time taken to reduce levels of E. coli by 90% was 6.5 h or less in all cases. In contrast, the amounts of time needed to reduce levels of F+ bacteriophage by 90% were considerably longer: 47.3 and 41.3 h (after short- and long-term exposures, respectively) in mussels and 54.6 and 60.8 h (after short- and long-term exposures, respectively) in oysters. No differences in the rates of reduction of indicators of viral pollution following exposure of the shellfish to either short- or long-term sewage contamination were observed. Further experiments were conducted with mussels to determine the relative distributions of E. coli and F+ bacteriophage in tissue before and during depuration. Prior to depuration the majority of E. coli organisms (90.1%) and F+ bacteriophage (87.3%) were detected in the digestive tract (i.e., the digestive gland and intestine). E. coli and F+ bacteriophage were reduced in all tissues except the digestive gland to undetectable levels following depuration for 48 h. Within the digestive gland, levels of F+ bacteriophage were reduced to 30% of initial levels, whereas E. coli was reduced to undetectable levels.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of mussel size, temperature, seston volume, food quality and volume-specific toxin concentration on the uptake rate of PSP toxins by mussels (Mytilus galloprovincialis Lmk)

The accumulation of paralytic shellfish poisoning (PSP) toxins by bivalves is a serious threat to public health all over the world. However, very little is known about the uptake kinetics of these toxins and the environmental factors that may modify this process. We have studied the effect of mussel size, temperature, seston volume, food quality, and volume-specific toxin concentration (VOSTOC), on the uptake rate of paralytic shellfish poisoning (PSP) toxins by mussels (Mytilus galloprovincialis), by means of a second order factorial experiment. Over a 3-day period, the mussels were fed artificial diets containing Alexandrium minutum AL1V (a PSP toxin producer), Tetraselmis suecica, Ensiculifera sp1 and silt, to the levels required by each treatment. Mussel size, seston volume and VOSTOC were found to be statistically significant when the total toxin accumulated per weight of wet tissue was considered. Mussel size affected the uptake negatively and latter two positively. The interactions, mussel size-VOSTOC and mussel size-food quality were also significant. The response was not linear as shown by the significance of the quadratic term of mussel size. Notwithstanding, when the PSP toxins accumulation per mussel was analysed, only one factor, the VOSTOC and the interactions, food quality-mussel size and food quality-seston volume, were found to be significant. VOSTOC was the most important factor in the accumulation of toxins, in our opinion, probably due to toxin assimilation being mainly regulated by the probability of contact between the toxins and the cellular walls of the digestive system. The size of the bivalve is also especially important because toxin concentration is usually calculated per weight of bivalve tissue and because the weight-specific ingestion increases with mussel size. The food quality, which was directly related to the assimilation of organic matter, had an inverse effect on toxin assimilation. In our opinion, this is probably due to the effect of inorganic particles in enhancing the disruption of Alexandrium cells. Temperature had no effect on the uptake rate except for the accumulation of the gonyautoxin GTX1.     

Does uptake of Alexandrium fundyense cysts contribute to the levels of PSP toxin found in the sea scallop, Placopecten magellanicus?

Atlantic sea scallops, Placopecten magellanicus, in most areas of the Bay of Fundy, New Brunswick, Canada, have year-round concentrations of paralytic shellfish posioning (PSP) toxins greater than the regulatory concentration of 80 μg STX eq. 100 g⁻¹ wet weight. Scallops (mean shell height of 10.7 cm, age 3–5 years) were collected by SCUBA and individually tagged near Parker Island, Bay of Fundy. Half were hung 2 m below the low tide water level and the remainder were placed on the bottom (11 m depth at low tide) under the scallops held at 2 m. Scallop, water and sediment samples were collected monthly for determination of concentrations of PSP toxins and Alexandrium fundyense.In October, 1993, mean concentrations of PSP toxins in digestive gland, and mantle were 3205 and 1018 μg STX eq. 100 g⁻¹ wet weight, respectively. Eight months later (June 1994), PSP concentrations in digestive glands from the surface and bottom had declined to 504 and 682 μg STX eq. 100 g⁻¹ wet weight, respectively, whereas those in the mantle had declined to 802 and 681 μg STX eq. 100 g⁻¹ wet weight. During July 1994, A. fundyense concentrations observed at Parker Island and offshore were 320 cells l⁻¹ and 14,200 cells l⁻¹, respectively. Subsequently, toxin concentrations in surface and bottom scallop digestive glands increased to 12,720 and 11,408 μg STX eq. 100 g⁻¹ wet weight, whereas concentrations in mantles increased to 2126 and 1748 μg STX eq. 100 g⁻¹ wet weight, respectively. Concentrations of PSP toxins in these tissues in October 1994 were similar to those measured in October 1993. Concentrations of PSP toxin were less than the regulatory concentration in the gonads and non-detectable in adductor muscles of all scallops sampled.There were no statistically significant differences in profiles for uptake and depuration of PSP toxins in scallops held at the surface compared to those from bottom, suggesting that A. fundyense cysts at the concentrations found in the sediment (45 cysts cm⁻³) did not contribute significantly to the year-round presence of PSP toxins within scallop tissues. The year-round occurrence of PSP toxin is probably due to accumulation during summer blooms followed by a very slow rate of depuration.     

Paralytic shellfish poisoning (PSP) toxin profiles and short-term detoxification kinetics in mussels Mytilus galloprovincialis fed with the toxic dinoflagellate Alexandrium tamarense

Mussels (Mytilus galloprovincialis) were experimentally contaminated with paralytic shellfish poisoning (PSP) toxins by being fed with the toxic dinoflagellate Alexandrium tamarense, and changes in toxin content and specific composition during the decontamination period were analyzed by high-performance liquid chromatography (HPLC). Toxins excreted by the mussels into the seawater were also recovered using an activated charcoal column and analyzed by HPLC. The predominant toxins in A. tamarense, mussels, and seawater were the N-sulfocarbamoyl-11-hydrosulfate toxins (C1,2) and carbamate gonyautoxins-1,4 (GTX1,4). There were no remarkable differences in the relative proportions of the predominant toxins within A. tamarense, mussels and seawater. Because the relative proportion of the various toxin analogues excreted by the mussels was similar to that within their tissues during detoxification, it appeared that the selective release of particular toxins by the mussels was unlikely. The total amount of toxin lost from mussels was nearly equal to that which was found dissolved in the seawater, suggesting that, at least the early stages of mussel detoxification, most losses can be accounted for by excretion.     

Distribution and selective elimination of paralytic shellfish toxins in different tissues of Octopus vulgaris

Octopus (Octopus vulgaris, Cuvier) plays a central role in the marine food web, being an important consumer with high metabolic rates and at the same time an important food item for higher predators. After harmful algal blooms, octopus can accumulate high levels of marine toxins trough trophic interrelationships. The aim of this study is to characterize the distribution of paralytic shellfish toxins (PSTs) in selected tissues of the O. vulgaris, in order to assess the translocation of toxins among organs with different physiological functions. Different retention times and selective elimination of particular toxin analogues were also investigated. Twenty three specimens of O. vulgaris were captured in Peniche (NW coast of Portugal) after PSTs have been detected in molluscan bivalves. Tissue matrices were dissected from organs with digestive function (digestive gland, stomach and salivary glands) and excretory function (kidneys and branchial hearts) and analyzed for toxin determination. Toxin analysis was carried out by high performance liquid chromatography with fluorescence detection (LC-FLD). PSTs were found in all tissues analyzed. The highest toxin concentrations were found in the digestive gland, reaching a maximum of 2980 μg STX equiv. kg⁻¹. The toxin profile was constituted by dcSTX, B1, C1 + 2, dcGTX2 + 3, dcNEO, STX and GTX2 + 3. A lower number of toxins were identified in the remaining organs, with B1 and dcSTX compromising more than 90% in molar fraction. Decarbamoyl saxitoxin was the most abundant toxin detected in digestive gland, stomach and salivary glands, while B1 was dominant in organs with excretory function. A positive correlation of concentrations of B1 and dcSTX were found in the organs analyzed. Results indicate that B1 and dcSTX are assimilated into the digestive gland in a similar proportion. Selective elimination of toxins with higher elimination of B1 and retention of dcSTX is suggested. This study contributes to better understanding of the dynamics of PSTs in O. vulgaris and the fate of PSTs in the food web.     

Dynamics of the phycotoxin domoic acid: accumulation and excretion in two commercially important bivalves

Batch cultures of the toxigenic diatomNitzschia pungens Grunow f.multiseries Hasle were fed to blue mussels (Mytilus edulis) and deep sea Atlantic scallops (Placopecten magellanicus) to elucidate conditions under which domoic acid (DA) was accumulated and excreted (depurated). Mussels accumulated the toxin to a maximum level of 13 g g^-1, at rates of 0.21 to 3.7 g h^-1 g^-1, dry weight. Accumulation efficiency (the proportion of accumulated DA to estimated net uptake) ranged from 1–5%. The highest filtration rate of 1.71 h^-1 occurred at concentrations of 4–8 × 10⁶ Nitzschia cells 1^-1 with no formation of pseudofeces. Depuration rates between fed and starved mussels over a 2 h test period were the same. The depuration rate of domoic acid was about 17% d^-1 and did not account for the low uptake efficiencies, so it is suggested that most of the DA is lost from mussels in the solution during the feeding process. Domoic acid accumulation in mussels was dependent on the amount of toxin available, which in turn was a function of the density and growth phase of theNitzschia population. Changes in filtration rate withNitzschia concentration and depuration rate with time can account for the DA levels of mussels collected during toxic episodes in Cardigan Bay, Prince Edward Island, Canada in 1988 and 1989.Scallops accumulated DA (0.39–1.3 g h^-1 g^-1, more slowly than mussels, however, accumulation efficiencies ranged from 5–100%. Filtration rates remained relatively low and constant at 0.081 h^-1. Scallops retained domoic acid longer than mussels, a fact which must be considered in the marketing of whole scallops for human consumption.     

Comparative study of the bioaccumulation and elimination of trace metals (Cd,Pb, Zn,Mn and Fe) in the digestive gland,gills and muscle of bivalve Pinna nobilis during a field transplant experiment

The purpose of this study was to investigate the long-term bioaccumulation and elimination of Cd, Pb, Mn, Zn and Fe by Pinna nobilis tissues after their 90 day-transplantation period at Téboulba fishing harbor. During the transplantation period, the Cd, Pb, Mn, Zn and Fe concentrations in the different tissues of the mussels were measured before and after exposure period. Metal (Cd, Pb, Mn, Zn and Fe) accumulation in P. nobilis mussels varied depending on the analyzed tissue and the caging times. Notable differences in Cd, Pb, Mn, Zn and Fe accumulation patterns within the digestive gland, gills and muscle were found and may be due to the ability of each tissue to accumulate metals. During the depuration phase, the elimination of Cd, Pb, Mn, Zn and Fe depended on the target tissue and the metal speciation. Cd, Pb, Mn and Fe were eliminated rapidly from one organ and increased in other when compared to those of 90 day transplanted mussels. The increase of metal loads during the elimination phase is not clear and particularly what kind of processes is responsible for such response. However, it is reasonable to assume that metals increase is related to the existence of an accumulation/detoxification mechanism, which involves the transport of metals from an organ to another. The data obtained indicate that because of the significantly high quantities of Cd, Pb, Mn, Zn and Fe accumulated during the exposure phase, the transplanted mussels are suitable bioindicators for monitoring trace metals in marine ecosystem.     

Age-dependence of metabolism in mussels Mytilus edulis (L.) from the White Sea

Age structure, natural mortality and growth, as well as age- and size-dependent changes in parameters of energy metabolism were studied in blue mussels Mytilus edulis (L.) from the White Sea. Mussels were sampled in August (Summer sample, SS) and October (Autumn sample, AS) and contained animals of three size groups, 2-9 years old. Field data showed an increase of mortality of mussels and strong decrease in growth rates after 6 years of age. Absolute tissue growth increment (AI) reconstructed from winter growth marks on the shells decreased with age and was strongly size-dependent, while relative tissue growth increment (RI) did not depend on size of the animals. Respiration rates and citrate synthase activity demonstrated power regression versus tissue weight with regression coefficients -0.231 and -0.170, respectively. After weight correction both parameters showed a decrease with increasing age. ATP and phosphagen levels also showed a pronounced decrease in animals older than 5-6 years despite considerable differences in the absolute values of both parameters in SS and AS. pH(i) in mussels was also age-dependent and decreased with increasing age after 5 years. In air exposed mussels, pH(i) was reduced only at young age such that pH(i) was low and constant within the whole age range. Our data give evidence that aerobic metabolic rate in M. edulis from the studied population declines when animals reach an age of about 6 years. The decrease in oxygen consumption reflects the drop in mitochondrial respiration, which is mirrored by the decrease in CS activity. A concomitant fall in ATP turnover may include a downregulation of the mechanisms of acid-base regulation. pH(i) will then approach equilibrium indicated by lower pH(i) values in older animals. Our data suggest that intrapopulational comparisons of physiological parameters in mussels should take into account age composition of compared samples.     

In vitro transformation of PSP toxins by different shellfish tissues

Many in vivo shellfish feeding experiments have been carried out in order to investigate the fate of PSP toxins in the marine food chain. A focal point of these studies concerns the species- and tissue-specific differences in toxin metabolism. However, tissue specific effects are often overlapped by selective toxin retention as well as transfer between individual compartiments. In in vitro experiments presented here digestive tissue and adductor homogenates of 10 shellfish species (bivalvia: Mytilus edulis, Crassostrea gigas, Cardium edule, Arctica islandica, Ensis ensis, Modiolus modiolus, Mactra stultorum, Pecten maximus as well as two snails: Littorina littorea and Buccinum undatum) were incubated with an extract of the toxic strain Alexandrium fundyense CCMP 1719. After incubation, changes in the toxin pattern could be observed in all samples with significant differences occuring between both the species and tissues. The greatest metabolic activity was found in digestive tissue samples. Among the organisms, the species with a non-filtering lifestyle, L. littorea and B. undatum, showed the highest conversion rates. Interestingly, the high metabolic transformation rate of the PSP toxins was accompanied with a fast reduction (up to 73%) of toxicity in the homogenates.     

The use of the probability model for an estimation of a infection rate of White Sea mussels (MYtilus edulis) by Metacercariae Himasthla elongata (Trematoda: Echinostomidae)

A comparison of simple probability analytic model of infection rate depending on host's age with natural infection rate of mussels (Bivalvia: Mythilidae) with metacercariae Himasthla elongata (Trematoda: Echinostomidae) was carried out. Data on the natural rate of infection were accumulated during 3 years; 1152 individuals M. edulis were collected in two horizons within fucoid zone of the Kruglaya inlet and the Chupa inlet of the Kandalaksha bay (White Sea). A size of shell and number of H. elongata metacercariae were defined for each mussel using compressive dissection technique. The infection of mussels per year within our model is considers as independent evens: Pn = 1 - (1 - p)n, where n is the age of mussels, Pn is the theoretical part of infected n-year mussels, p is the probability of infection within one year. The probability of infection within year is assumed equal for every age of host. The estimate of probability of infection per year on the basis of sample of n-year's mussels was calculated as Pn = 1 - n square root of 1 - I(n), where n is the age of mussels, I(n) is the part of infected n-year mussels. The retransformed weighted average value of aresine-transformed p'n was used as p in our model (p = 0.3476). Statistically significant differences between empirical and theoretical (calculated from our models on the basis this value) infection rates were not found (P > > 0.05 chi 2-test). Moreover, statistical significant differences were absent (P > 0.05 Fisher exact test) in pairwise comparisons between empirical and theoretical infection rates for each age of mussels. The model does not take into consideration an effect of such factors as host's resistance, host's migration and increase of mortality in infected hosts. The absence of significant differences between the empirical and theoretical infection rates allows to suggest, that mentioned factors under the conditions of the Kruglaya inlet do not influence essentially onto infection of mussels with metacercariae H. elongata. This conclusions is in certain inconsistency with essential differences in such characteristic as an individual resistance of mussels to the infection with metacercariae H. elongata, detected in experiments in vitro (Gorbushin, Levakin, unpublished data). Analysis of intensity of the invasion of metacercariae H. elongata into mussels allows to suggest the existence of differential death rate of the hosts, which is exhibited in individuals over 7 years old. Studied example of mussels infected with metacercariae H. elongata under conditions of the Kruglaya inlet shows that the simple probabilistic model of the natural infection rate is usable for this kind of investigation. Our study also allows to conclude that in this case the infection rate of hosts is mainly determined by stochastic reasons. However, in some cases the probability of infection rate may not depend on the age and size of the host. The study of infection rate can not be used for analyses of individual differences of hosts in a resistance to parasites and an infection ability of the parasite.     

Detection of bacteria originally isolated from Alexandrium spp. in the midgut diverticula of Mytilus edulis after water-borne exposure

Bacteria associated with toxic dinoflagellates have been implicated in the production of paralytic shellfish poisoning (PSP) toxins, but it has not been substantiated that bacteria are truly capable of autonomous PSP toxin synthesis or what role bacteria may play in shellfish toxification. In this study, different putatively PSP toxin producing bacteria originally isolated from toxic Alexandrium spp. were exposed to the blue mussel Mytilus edulis. To document that these bacteria accumulated in the digestive tract of the mussels, hybridization techniques that use rRNA targeted oligonuceotides for in situ identification of these bacteria were applied. The mussel hepatopancreas was dissected and paraffin and frozen sections were made. The dissected glands were hybridized with digoxigenin-labelled 16S rRNA oligonucleotide probes. Results demonstrate that mussels will readily uptake and accumulate these bacteria in the hepatopancreas. However, the mussels were not rendered toxic by the ingestion of the bacteria as determined by HPLC with UV detection for PSP toxins and determination of sodium channel blocking activity using the mouse neuroblastoma assay. Thus, although the role that bacteria play in mussel toxification remains unclear, methods are now available which will aid in further investigation of this relatively unexplored area.     

Paralytic shellfish toxins in zooplankton, mussels, lobsters and caged Atlantic salmon, Salmo salar, during a bloom of Alexandrium fundyense off Grand Manan Island, in the Bay of Fundy

Substantial mortalities of Atlantic salmon (Salmo salar) at two aquaculture sites in Long Island Sound, off Grand Manan Island, Bay of Fundy (BoF) (New Brunswick, Canada) in September 2003, were associated with a bloom of Alexandrium fundyense (>3 × 10⁵ cells L⁻¹), a dinoflagellate alga that produces toxins which cause paralytic shellfish poisoning (PSP). Cells of A. fundyense collected from surface waters while fish were dying had total paralytic shellfish (PS) toxin concentrations of 70.6 pg STX equiv. (saxitoxin equivalents) cell⁻¹ and PS toxin profiles rich in carbamate toxins (78.2%). The zooplankton sampled contained PS toxins (63.1 pg STX equiv. g⁻¹ wet wt) and the toxin profile matched that of A. fundyense cells.Mean PS toxin levels were low (<4 μg STX equiv. 100 g⁻¹ wet wt) in stomach, gill and muscle tissues of moribund salmon, suggesting that PS toxins are very lethal to salmon.The PS toxin concentrations in blue mussels (Mytilus edulis) growing on the salmon cages (37; 526 μg STX equiv. 100 g⁻¹ wet wt) were the highest recorded to date from this region. Their PS toxin profiles showed enhanced carbamate contents (85.5%) compared with that found in A. fundyense. Blue mussels collected from an adjacent Canadian Food Inspection Agency (CFIA) monitoring site in Grand Manan had PS toxin concentrations of 4214 and 150 μg STX equiv. 100 g⁻¹ wet wt in late September and December, respectively, well above the regulatory limit (RL), and horse mussels (Modiolus modiolus) collected in late September had PS toxin concentrations of 2357 μg STX equiv. 100 g⁻¹ wet wt. Detoxification under laboratory conditions suggested that blue mussels may require up to 19 weeks for elimination below RL when they accumulate these high concentrations of PS toxins. This depuration period may be shorter in the field.PS toxin levels above RL were detected in hepatopancreatic tissues of lobster (Homarus americanus), with lower levels (<16 μg STX equiv. 100 g⁻¹ wet wt) in tail muscle and gills.These results illustrate the movement of PS toxins through the marine food chain following an A. fundyense bloom in the BoF, and support earlier studies suggesting that kills from the region of zooplanktivorous fish, such as herring (Clupea harengus harengus), can be attributed to blooms of A. fundyense. This is the first reported incident of PSP associated with mortalities of caged Atlantic salmon in the BoF. Analyses of muscle tissues and viscera from the affected salmon indicated that any portion would not be a health hazard if consumed.     

Relationship between physiological measurements (SFG -scope for growth-) and the functionality of the digestive gland in Mytilus galloprovincialis

The present study was aimed to establish the relationship between the functionality of the digestive gland and physiological rates including SFG (scope for growth) in wild mussels, Mytilus galloprovincilis. The experimental set-up consisted in the evaluation of changes in the morphology of the gland, as well as in the activity of some key digestive enzymes (amylase, laminarinase, cellulase and protease) within a broad range of SFG obtained through manipulation of food ration. The higher SFG values were correlated to an increase in both the size of the digestive gland and the activities of enzymes when expressed in relation to individual. In contrast, no clear relations were observed when the activity of enzymes was expressed in relation to soluble protein, with the exception to amylase. The higher protease activities measured in mussels showing lower SFG may reflect an initial stage of catabolic processes intended to compensate the energy deficit produced by food restriction. The potential use of parameters measured in digestive glands in studies of marine pollution was discussed.     

Removal of faecal indicator bacteria and bacteriophages from the common mussel (Mytilus edulis) under artificial depuration conditions

Artificial self-purification (depuration) of mussels (Mytilus deulis) was undertaken at three temperatures, under conditions similar to those likely to be experienced in the commercial shellfish industry of the UK. During a 72 h depuration period, samples of mussel flesh were examined for three faecal indicator bacteria, Escherichia coli, Group D faecal streptococci and sulphite-reducing Clostridium spores, and two types of bacteriophage. There was a statistically significant difference in the elimination rate of faecal indicator bacteria compared with the slower rate for both bacteriophages.     

Soluble nitrogen and phosphorus excretion of exotic freshwater mussels (Dreissena spp.): potential impacts for nutrient remineralisation in western Lake Erie

1. Recent increases in phytoplankton biomass and the recurrence of cyanobacterial blooms in western Lake Erie, concomitant with a shift from a community dominated by zebra mussels (Dreissena polymorpha) to one dominated by quagga mussels (D. bugensis), led us to test for differences in ammonia‐nitrogen and phosphate‐phosphorus excretion rates of these two species of invasive molluscs. 2. We found significant differences in excretion rate both between size classes within a taxon and between taxa, with zebra mussels generally having greater nutrient excretion rates than quagga mussels. Combining measured excretion rates with measurements of mussel soft‐tissue dry weight and shell length, we developed nutrient excretion equations allowing estimation of nutrient excretion by dreissenids. 3. Comparing dreissenid ammonia and phosphate excretion with that of the crustacean zooplankton, we demonstrated that the mussels add to nitrogen and phosphorus remineralisation, shortening nitrogen and phosphorus turnover times, and, importantly, modify the nitrogen and phosphorus cycles in Lake Erie. The increased nutrient flux from dreissenids may facilitate phytoplankton growth and cyanobacterial blooms in well‐mixed and/or shallow areas of western Lake Erie.     

Influence of Salinity on the Structure and the State of Bivalve Mytilus galloprovincialisPopulations

The influence of salinity on the structure and status of mussel Mytilus galloprovincialispopulations in the Black Sea was examined. Lowering salinity results in an increase in mortality rate and a decrease in numbers, biomass, juvenile recruitment, growth rates, and annual production. Low salinity produces changes in the size, age, sex, and phenotypic structure of mussel populations, namely, a decrease in the average size and age of mussels and an increase in the proportion of females and heterozygote deficiency.