Individual Bivalves Research Articles

Studi Komparasi Kuantitas Bivalvia pada Zona Intertidal di Pantai Ntana Kabupaten Bima sebagai Upaya Penyusunan Brosur Konservasi

Bivalves belong to the Phylum mollusca. Bivalve are found and live in the Intertidal area. Ntana Beach is the easiest area and has the most interaction with human activities, because this area is a transitional area between aquatic ecosystems and land ecosystems. This study aims to: 1) identify the types of bivalves that make up the Intertidal zone on the Ntana coast, Bima Regency; 2) analyzing the abundance, diversity index, and evenness of Bivalvia in the Intertidal zone on the Ntana coast, Bima Regency; 3) describe the population of bivalve species that dominate the Intertidal zone on the Ntana coast, Bima Regency; 4) analyzing the abundance of bivalves in the sandy, muddy and rocky substrate areas on the Ntana beach, Bima Regency; 5) analyzing the diversity of bivalve species in the area of ​​sandy substrate, muddy substrate, and coral substrate on the Ntana beach, Bima Regency; 6) knowing the differences in the dominance of Bivalvia in the sandy, muddy and rocky substrate areas on the Ntana beach, Bima Regency; and 7) to develop research results on a comparative study of the quantity of bivalves in the intertidal zone on the Ntana coast, Bima district as an effort to prepare a conservation brochure. This type of research is descriptive comparative. Sampling used a 1x1 M plot. The results showed that as many as 540 individual bivalves consisting of 15 species were found on the Ntana beach, Bima district. 15 species of bivalves found include Anadara antiquata, Anadara granosa, Anadara brasilliana, Panopea generosa, Fausta pultenei, Dosina crebra, Eurytellina alternate, Dosina discus, Nactula acuta, Gafrarium divaricatum, Dosinia exoleta, Caestoderma edule, Gafrarium disparm, Cyclocardia ventricosa, and Crassostrea gigas. The abundance on sandy and silty substrates is categorized as moderate, whereas on coral substrates it is categorized as low. Species diversity on rocky substrates is less, whereas on muddy and sandy substrates each has a fairly high level of species diversity. The evenness value on sandy and muddy substrates is close to zero (0), so that the evenness of Bivalvia species on both substrates is not evenly distributed. There are no species that dominate other species because D <0.5. The average value of the brochure validation test is 75.4%, with this result, the brochures that have been compiled are in the good category and do not need to be revised.

Is micropollutant-loaded powdered activated carbon from a wastewater treatment plant toxic to the bivalve Corbicula sp.?

BackgroundIn order to reduce emissions of micropollutants (MPs) via effluents of wastewater treatment plants (WWTPs), additional treatment steps are suggested and already deployed in selected WWTPs. Next to advanced oxidation processes, the application of powdered activated carbon (PAC) is considered a promising and suitable option as MP removal rates of 80% and more can be achieved. However, this method might also hold a drawback as a complete retention of PAC applied within the WWTP cannot always be guaranteed. Hence, small amounts of MP-loaded PAC can enter receiving waters with potentially negative consequences for aquatic organisms. The present study investigated possible effects of MP-loaded PAC from a WWTP as compared to unloaded, native PAC on the bivalve Corbicula sp. in a 10-week exposure experiment. The PAC types were administered in concentrations of 1, 10 and 100 mg/L in a semi-static sediment–water system.ResultsMolecular biomarker responses for xenobiotic metabolism (i.e., glutathione-S-transferase (GST)) and oxidative stress (i.e., catalase (CAT) activity and lipid peroxidation) were analyzed and in none of the treatments, significant differences to the control could be detected, except for the CAT activity in the 1 mg/L PACWWTP treatment. Moreover, the filtration rate of individual bivalves was measured after 5 and 10 weeks of exposure and compared to the initial filtration rate with the result that the presence of PAC did not affect the filtration rate of Corbicula sp. In summary, despite the selection of sensitive endpoints and a comparatively long exposure period, no significant effects were detected for unloaded and MP-loaded PAC even at the highest test concentration, which is far away from environmental relevance.ConclusionsThese results give an auspicious perspective for the application of PAC in WWTPs. Even when small PAC leakages from WWTPs occur, adverse effects for aquatic organisms appear to be neglectable based on our findings.

Ecophysiology and ecological limits of symbiotrophic vesicomyid bivalves (Pliocardiinae) in the Southern Ocean

Geothermal energy provides an important resource in Antarctic marine ecosystems, exemplified by the recent discovery of large-sized chemosymbiotic vesicomyid bivalves (subfamily Pliocardiinae) in the Southern Ocean. These clams, which we identified as Archivesica s.l. puertodeseadoi, have been reported as dead shells in areas previously covered by Larsen A and B ice shelves (eastern Antarctic Peninsula) and as live animals from active hydrothermal sites in the Kemp Caldera (South Sandwich Arc) at depths of 852–1487 m. Before, A. puertodeseadoi was known only from its type locality in the Argentine Sea, so we considerably extend the range of the species. Observations taken by remotely operated vehicle (ROV) footage show that the clams can live buried in sediment, or epilithically on the surface of rocks in diffuse geothermal flow. Experimental respirometry was conducted at surface pressure on individual bivalves acclimated to either their habitat temperature (4 °C) or elevated temperature (10 °C). The range of standard metabolic rates, from 3.13 to 6.59 (MO2, μmol O2 h−1 g−1 dry tissue mass), is similar to rates measured ex situ for other species in this clade, and rates did not differ significantly between temperature groups. Taken together, these data indicate a range of ecophysiological flexibility for A. puertodeseadoi. Although adapted to a specialist mode of life, this bivalve exploits a relatively broad range of habitats in the Southern Ocean: within sulphidic sediments, epilithically in the presence of diffuse sulphidic flow, or in deep methane-enriched seawater trapped under ice.

Variation in Glycogen Distribution among Freshwater Bivalve Tissues: Simplified Protocol and Implications.

Glycogen is a primary metabolic reserve in bivalves and can be suitable for the evaluation of bivalve condition and health status, but the use of glycogen as a diagnostic tool in aquaculture and biomonitoring is still relatively rare. A tissue biopsy combined with a simplified phenol-sulfuric acid method was used in this study to evaluate the inter- and intraindividual variation in the glycogen concentrations among several tissues (foot, mantle, gills, adductor muscle) of the unionid bivalve, the duck mussel Anodonta anatina. This short report documents that individual bivalves differ in the spatial distribution of glycogen among tissues. Sampling of different types of tissues can cause distinct results in the evaluation of energetic reserves at the individual level. At the same time, spatial variability in glycogen content has the potential to provide a more detailed evaluation of physiological conditions based on tissue-specific glycogen storage. The results obtained and the simplified methodology provide a new opportunity for researching the energetic reserves and health status of freshwater mussels in various applications.

Ecological drivers and habitat associations of estuarine bivalves

Community composition of the infaunal bivalve fauna of the St. Lucie Estuary and southern Indian River Lagoon, eastern Florida was sampled quarterly for 10 years as part of a long-term benthic monitoring program. A total of 38,514 bivalves of 137 taxa were collected and identified. We utilized this data, along with sediment samples and environmental measurements gathered concurrently, to assess the community composition, distribution, and ecological drivers of the infaunal bivalves of this estuary system. Salinity had the strongest influence on bivalve assemblage across the 15 sites, superseding the influences of sediment type, water turbidity, temperature and other environmental parameters. The greatest diversity was found in higher salinity euhaline sites, while the greatest abundance of individual bivalves was found in medium salinity mixohaline sites, the lowest diversity and abundances were found in the low salinity oligohaline sites, demonstrating a strong positive association between salinity and diversity/abundance. Water management decisions for the estuary should incorporate understanding of the role of salinity on bivalve diversity, abundance, and ecosystem function.

No evidence for impacts to the molecular ecophysiology of ion or CO2 regulation in tissues of selected surface-dwelling bivalves in the vicinity of a sub-seabed CO2 release

Whilst sub-seabed Carbon Capture and Storage (CCS) has the potential to remove a significant proportion of anthropogenic CO2 emissions at source, research is necessary to constrain the environmental impacts of potential future gas leaks from storage reservoirs. The QICS project (Quantifying and Monitoring Potential Ecosystem Impacts of Geological Carbons Storage) was established to improve our understanding of these potential impacts and to develop tools and best practice for monitoring sub-seabed CCS reservoirs. Exposure to increased environmental CO2 has been shown to raise the tissue pCO2 of many marine invertebrate species, leading to tissue acidosis and perturbations in both ion transport and bicarbonate buffering. These disturbances can cause downstream effects, seen as metabolic depression in susceptible organisms, compromising the role of particular species within an ecosystem and even causing the local extinction of species groups. To monitor the potential impact to surficial benthic megafauna, cages of bivalves (the common mussel Mytilus edulis Linnaeus, 1758 and the king scallop Pecten maximus (Linnaeus, 1758)) were deployed at the gas release site and at a reference site—both within Ardmucknish Bay, Oban, Scotland. Replicate individuals were sampled at six time points over a 125-day period, which spanned both the 37-day injection and recovery phases of the experiment, in order to establish impacts to molecular physiology. Samples of bivalves were also simultaneously sampled from a reference site within the bay in order to contrast changes in physiology induced by the gas release with naturally variability in the physiological performance of both species. We present data on changes in the transcription of genes coding for key ionic and carbon dioxide regulatory proteins. There was no evidence of gene regulation of either selected carbonic anhydrases (CAx genes) or the alpha subunit of sodium potassium ATPAses (ATP1A genes) in individual bivalves collected from the CO2 gas release site, in either species. In the common mussel M. edulis there was only evidence for changes with time in the expression of genes coding for different classes of carbonic anhydrase. It was therefore concluded that the effects of the plume of elevated pCO2 on ion-regulatory gene transcription were negligible in both species. Whilst the analysed data from this current study do not constitute an impediment to the continued development of sub-seabed CCS as a climate mitigation strategy, further modelling is necessary to predict the consequences of larger or longer term leaks. Further analysis is also required in order to constrain the potential physiological impacts of gas leaks to benthic infaunal species and understand the mechanism of possible avoidance behaviour recorded in burrowing heart urchins Echinocardium cordatum (Pennant, 1777).

The effect of an invading filter-feeding bivalve on a phytoplankton assemblage from the Paraná system: a mesocosm experiment

The effect of different concentrations of the bivalve Limnoperna fortunei on the algal density and structure and its filtration rate was estimated in a mesocosm experiment. The experiment was carried out using containers of 200 L and three treatments: Control (without bivalves), C1 (with 128 individual bivalves), and C2 (with 256 individual bivalves). Decrease in phytoplankton density was detected in bivalve treatments after 6 h. A decrease of 52% and 86% of the initial density was measured in C1 and C2, respectively, after 48 h. All algae groups showed substantial decrease in densities (>60%) and the composition of the algae assemblages changed in the presence of the bivalve. In particular, there was an increase in the density of Flagellates. The maximum estimated bivalve filtration rate was 357 mL ind−1 h−1 at 28°C. Our results suggest that the invading bivalves could significantly affect both the plankton density and assemblage structure in natural systems.

In situ evidence for pre-capture qualitative selection in the tropical bivalve Lithophaga simplex

Few feeding studies have been performed on tropical bivalves, and in situ feeding studies are lacking altogether. We investigated retention efficiencies for natural particles in the coral-boring tropical mytilid Lithophaga simplex. Using the in situ InEx technique (Yahel et at. 2005; Limnol Oceanogr Methods 3:46-58) SCUBA divers collected samples from the water inhaled and exhaled by undisturbed bivalves at the coral reef of Eilat (Gulf of Aqaba). Particle retention efficiencies were determined using flow cytometry analysis of the paired water samples. The photosynthetic bacterium Synechococcus (0.9 +/- 0.1 mu m) and larger eukaryotic algae (1 to 10 mu m) were preferentially retained by the bivalve with removal efficiencies of up to 90 % (1996 to 2000: averages of 69 +/- 14 % and 60 +/- 17 %, respectively, n = 74 individual bivalves). The minute photosynthetic bacterium Prochlorococcus (0.4 +/- 0.1 mu m) was also moderately retained (41 +/- 19%). Only a small proportion of the non-photosynthetic bacteria (0.3 +/- 0.1 mu m) were retained (5 +/- 18%, median of 9%), despite their numerical dominance in the plankton and considerable size overlap with Prochlorococcus. Size-independent preferential retention was also observed within particle types: (1) L. simplex more efficiently retained Prochlorococcus and picoeukaryotic algal cells with higher chlorophyll content and (2) the small fraction of non-photo synthetic bacteria retained did not differ in size, but bad higher nucleic acid content (compared to the inhaled population) an indicator for viable and active bacteria. We conclude that particle retention is not strictly size-dependent in L. simplex, and probably involves other cell attributes such as cell surface properties and/or motility.

Clearance rates of the great scallop (Pecten maximus) and blue mussel (Mytilus edulis) at low natural seston concentrations

Great scallop, Pecten maximus, and blue mussel, Mytilus edulis, clearance rate (CR) responses to low natural seston concentrations were investigated in the laboratory to study (1) short-term CR variations in individual bivalves exposed to a single low seston diet, and (2) seasonal variations in average CR responses of bivalve cohorts to natural environmental variations. On a short temporal scale, mean CR response of both species to 0.06 μg L−1 chlorophyll a (Chl a) and 0.23 mg L−1 suspended particulate matter (SPM) remained constant despite large intra-individual fluctuations in CR. In the seasonal study, cohorts of each species were exposed to four seston treatments consisting of ambient and diluted natural seston that ranged in mean concentration from 0.15 to 0.43 mg L−1 SPM, 0.01 to 0.88 μg L−1 Chl a, 36 to 131 μg L−1 particulate organic carbon and 0.019 to 0.330 mm3 L−1 particle volume. Although food abundance in all treatments was low, the nutritional quality of the seston was relatively high (e.g., mean particulate organic content ranged from 68 to 75%). Under these low seston conditions, a high percentage of P. maximus (81–98%) and M. edulis (67–97%) actively cleared particles at mean rates between 9 and 12 and between 4 and 6 L g−1 h−1, respectively. For both species, minimum mean CR values were obtained for animals exposed to the lowest seston concentrations. Within treatments, P. maximus showed a greater degree of seasonality in CR than M. edulis, which fed at a relatively constant rate despite seasonal changes in food and temperature. P. maximus showed a non-linear CR response to increasing Chl a levels, with rates increasing to a maximum at approximately 0.4 μg L−1 Chl a and then decreasing as food quantity continued to increase. Mean CR of M. edulis also peaked at a similar concentration, but remained high and stable as the food supply continued to increase and as temperatures varied between 4.6 and 19.6°C. The results show that P. maximus and M. edulis from a low seston environment, do not stop suspension-feeding at very low seston quantities; a result that contradicts previous conclusions on the suspension-feeding behavior of bivalve mollusks and which is pertinent to interpreting the biogeographic distribution of bivalve mollusks and site suitability for aquaculture.

Feeding current characteristics of three morphologically different bivalve suspension feeders, Crassostrea gigas, Mytilus edulis and Cerastoderma edule, in relation to food competition.

Introduced Pacific oysters (Crassostrea gigas) have shown rapid expansion in the Oosterschelde estuary, while stocks of native bivalves declined slightly or remained stable. This indicates that they might have an advantage over native bivalve filter feeders. Hence, at the scale of individual bivalves, we studied whether this advantage occurs in optimizing food intake over native bivalves. We investigated feeding current characteristics, in which potential differences may ultimately lead to a differential food intake. We compared feeding currents of the invasive epibenthic non-siphonate Pacific oyster to those of two native bivalve suspension feeders: the epibenthic siphonate blue mussel Mytilus edulis and the endobenthic siphonate common cockle Cerastoderma edule. Inhalant flow fields were studied empirically using digital particle image velocimetry and particle tracking velocimetry. Exhalant jet speeds were modelled for a range of exhalant-aperture cross-sectional areas as determined in the laboratory and a range of filtration rates derived from literature. Significant differences were found in inhalant and exhalant current velocities and properties of the inhalant flow field (acceleration and distance of influence). At comparable body weight, inhalant current velocities were lower in C. gigas than in the other species. Modelled exhalant jets were higher in C. gigas, but oriented horizontally instead of vertically as in the other species. Despite these significant differences and apparent morphological differences between the three species, absolute differences in feeding current characteristics were small and are not expected to lead to significant differences in feeding efficiency.

Effects of food availability and hypoxia on bivalves: the value of using multiple parameters to measure bivalve condition in environmental studies

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 298:205-218 (2005) - doi:10.3354/meps298205 Effects of food availability and hypoxia on bivalves: the value of using multiple parameters to measure bivalve condition in environmental studies J. Norkko1,2,4,*, C. A. Pilditch3, S. F. Thrush1, R. M. G. Wells2 1National Institute of Water and Atmospheric Research, PO Box 11-115, Hamilton, New Zealand2School of Biological Sciences, The University of Auckland, Private Bag 92019, Auckland, New Zealand3Department of Biological Sciences, University of Waikato, Private Bag 3105, Hamilton, New Zealand4Present address: Finnish Institute of Marine Research, PB 33, 00931 Helsinki, Finland *Email: joanna.norkko@fimr.fi ABSTRACT: Suspension-feeding bivalves are often included in environmental monitoring because of their trophic position, widespread occurrence and sensitivity to a wide range of environmental factors. Therefore various indices of bivalve condition and growth have been developed, including morphometric condition indices (CI), scope for growth (SFG) and nucleic acid ratios (RNA:DNA ratio, RNA:protein ratio or RNA concentration). The sensitivity of these 3 indices has not previously been compared in the same individual bivalves, yet they are likely to have different temporal scales of detectable response to environmental processes. In 2 laboratory experiments (10 and 24 d duration) we investigated the combined effect of food availability and sublethal hypoxia on RNA concentration, CI and SFG in juvenile clams Paphies australis. RNA and CI increased rapidly (5 d) following exposure to high food treatment, but only CI showed a negative influence of hypoxia. Although SFG was affected by both food availability and hypoxia, the patterns were opposite to those of RNA and CI. This anomaly could be explained by the instantaneous change in feeding rates and a slower response in respiration rate (which was correlated with CI) to the uniform conditions under which SFG was determined. Our results emphasise the importance of combined effects of environmental factors on bivalve growth, highlighting the overriding influence of food availability, and imply that a combination of measures will give a more accurate representation of growth rate. KEY WORDS: Nucleic acid ratios · RNA · Condition index · Scope for growth · Food availability · Hypoxia · Paphies australis Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 298. Online publication date: August 15, 2005 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2005 Inter-Research.

Divalent metal accumulation in freshwater bivalves: an inverse relationship with metal phosphate solubility

Whole soft tissue concentrations of Mn, Co, Ni, Cu, Zn, Pb, Cd and U were measured in two species of freshwater (unionid) bivalves ( Hyridella depressa and Velesunio ambiguus) from a minimally polluted site in the Hawkesbury-Nepean River, south-eastern Australia. Although the mean concentrations of metals in the tissue were similar for each bivalve species, their patterns of accumulation were dissimilar. For each metal, positive linear relationships between tissue concentration and shell length ( r 2=0.37–0.77; P≤0.001) and tissue dry weight ( r 2=0.29–0.51; P≤0.01) were found in H. depressa, but not in V. ambiguus. However, for both species, positive linear relationships were found between the tissue concentration of each divalent metal and Ca tissue concentration ( r 2=0.59–0.97; P≤0.001). For both bivalve species, the normalised rates of accumulation of the metals relative to increasing Ca concentration and/or size, were U≈Cd≥Pb≥Mn>Co≥Zn>Cu>Ni. The differential rates of accumulation of divalent metals are interpreted as being predominantly governed by their varying loss rates, which are controlled by the differing solubilities (log K sp values) of the metals in the phosphatic extracellular granules, the demonstrated major sites of metal deposition in the tissue of H. depressa and V. ambiguus. The rates of accumulation of Mn, Co, Zn, Cu and Ni were linearly and inversely related ( r 2=0.91–0.97; P≤0.001) to their solubilities as hydrogen phosphates, a finding consistent with the bioaccumulation model previously developed for the alkaline-earth metals. However, for U, Cd and Pb, this linear inverse relationship did not continue to hold, i.e. their rates of accumulation did not increase with decreasing solubility. However, these results are still consistent with the model if U, Cd and Pb are so insoluble in the granules of H. depressa and V. ambiguus over their lifetime (up to approx. 50 years) that there is effectively no loss of these metals, and hence, no differential between their rates of accumulation. The present results reaffirm the use of Ca tissue concentration to predict the tissue concentrations of other divalent metals by explaining up to 94 and 97% of the variability between individual bivalves of H. depressa and V. ambiguus, respectively. The use of Ca tissue concentration to effectively minimise the inherent variability between individuals in their metal tissue improves the ability of an investigator to discern smaller spatial and/or temporal differences in the metal tissue concentrations of these bivalves, and thus to detect metal pollution.

Comparison of metal uptake rate and absorption efficiency in marine bivalves

Recent studies have quantified extensively metal assimilation efficiency from ingested food sources in aquatic invertebrates. Metal absorption efficiency (alpha) from the dissolved phase is analogous to metal assimilation efficiency, but it remains poorly defined and quantified. In this study, the alpha of four trace metals [Cd, Cr(VI), Se(IV), and Zn] was determined in three species of marine bivalves (green mussel [Perna viridis], black mussel [Septifer virgatus], and clam [Ruditapes philippinarum]). Individual bivalves were first measured for their clearance rates, followed by measurements of the metal influx rate, after which the metal alpha and the uptake rate constant (Ku) were then computed. Among the four metals considered, the highest Ku and alpha were found for Zn, followed by Cd > Cr(VI) > Se(IV). The Ku values were comparable between the two mussels but were 1.8- to 3.3-fold lower in the clams. Interspecific difference in metal Ku was strongly related to, but intraspecific difference in Ku was not affected by, the bivalve's clearance rate. Interspecific difference in metal alpha was smaller than the metal Ku and was independent of the clearance rate, whereas the intraspecific difference in metal alpha correlated with the individual variations of the clearance rate. Within each bivalve species, a significant negative correlation was found between the metal alpha and the clearance rate, implying that an individual pumping a greater amount of water was coupled to a lower alpha. Significant correlation between the alpha of four metals was also documented in all three species of bivalves. Thus, metal bioavailability from the aqueous phase was directly related to the physiological conditions of the animals. Both the aqueous chemistry and the physiology of the animals can be important in affecting metal bioavailability from the dissolved phase.

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.

Kinetics of 45Ca, 60Co, 210Pb, 54Mn and 109Cd in the tissue of the freshwater bivalve Velesunio angasi: further development of a predictive and mechanistic model of metal bioaccumulation

A theoretical and experimental study was performed to determine the kinetics of 45Ca, 60Co, 210Pb, 54Mn and 109Cd in the whole soft tissue of the unionid bivalve Velesunio angasi. This investigation further tested the hypothesis, developed previously for the alkaline-earth metals, that the biological half-life of a metal in soft tissue is related to its solubility when deposited in the extracellular granules of the bivalve. This hypothesis was tested for the above radionuclides (tracers of the stable metals) by a comparison of (a) a qualitative a priori prediction of their biological half-lives in bivalve tissue, based on critically evaluated log Ksp values for their respective hydrogen phosphate salts, and calibrated to previous experimentally determined rates of loss for 45Ca and 226Ra, with (b) their empirical biological half-lives that were investigated experimentally using the radionuclides 45Ca, 60Co, 210Pb, 54Mn and 109Cd. The results of the experimental investigation showed that the mean values calculated for the biological half-lives of 45Ca and 60Co in the tissue were 106 and 121 days, respectively, but there was no significant (P > 0.05) loss of 210Pb, 54Mn or 109Cd from the soft tissue over 160 days, when bivalves were exposed to radionuclide-free water. A chemical model was developed from first principles that quantitatively explains the kinetic mechanisms that underlie the differential rates of loss of divalent metals from the extracellular granules of V. angasi. The experimental results were consistent with the predictions of the model; however, some investigational limitations were evident, and these are discussed. The uptake of each radionuclide into the bivalve tissue tended to be linear, but the variation in tissue concentration, between individual bivalves, increased with the period of exposure. Significant (P < 0.001) positive correlations were found between tissue concentrations of each radionuclide pairing in both the uptake and loss phases of the experiment, indicating that individual bivalves were internally consistent in the way that they metabolised these radionuclides.

Two-Stage Neomorphism of Jurassic Aragonitic Bivalves: Implications for Early Diagenesis

ABSTRACT Aragonitic bivalves in Middle Jurassic paralic limestones from Lincolnshire (Eastern England) have been neomorphically replaced by inclusion-rich calcite spar. Textural features of spar are analogous to examples from other calcitized Jurassic molluscs, but Lincolnshire bivalves show evidence for two distinct stages of replacement. Staining, cathodoluminescence, and backscatter scanning electron microscopy reveal an initial volumetrically minor and frequently fabric-selective replacement by nonferroan calcite, with most of the remaining skeletal aragonite subsequently replaced by ferroan calcite spar. Stable-isotope data from individual bivalves define a negative covariant mixing trend ranging from early, relatively 13C-depleted and 18O-enriched nonferroan calcite (d13C = -2 PDB), to ferroan calcite with composition similar to associated late pore-filling cements (d13C » +2 PDB, d1 O » -7 PDB). The early diagenetic end member precipitated from depositional pore fluids, with bicarbonate supplied both from dissolution of skeletal aragonite and bacterial oxidation of organic material. In contrast, ferroan spar precipitated during burial diagenesis and dewatering of shales surrounding the limestone. Bulk trace-element signatures of the bivalves are dominated by late ferroan calcite, but electron probe microanalysis and intrinsic blue cathodoluminescence shows that early calcite contains negligible amounts of Fe, Mn, and Mg. Together with isotopic and fabric data this indicates that early neomorphism occurred at shallow depths and may even have begun at the sediment-water interface. In the absence of through-flowing meteoric waters, early replacement did not proceed via an inward-migrating neomorphic front. Instead, calcitization was initiated at numerous individual reaction centers throughout the shells and was principally controlled by the distribution of the skeletal organic matrix. This contrasts strongly with most previous reports of aragonite neomorphism during arly diagenesis.

Feeding radius, burying depth and siphon size of Macoma balthica and Scrobicularia plana

This paper investigates whether siphon weight limits the elongation of the siphon of deposit-feeding benthic bivalves under natural conditions. Were this to be so, it would imply that foraging and predator avoidance place conflicting demands on these animals, since an increase in the feeding radius on the surface would be associated with a decrease in the burying depth, and vice versa. The paper presents methods with which to measure siphon length and equations to transform siphon weight to siphon length in two benthic bivalves, Scrobicularia plana and Macoma balthica. Relatively heavy siphons are longer, but also thicker, than lightweight ones. We conclude that most individual bivalves stretch their siphons fully while feeding. However, bivalves with heavy siphons keep part of the siphon in reserve within the shell. Siphon cropping therefore results in an immediate reduction in siphon length, unless the siphon is heavy and a reserve is available. The feeding radius of M. balthica and S. plana is a linear function of shell size. S. plana use half of their siphon length to feed on the surface and the other half to bury themselves, but if the siphon weight is below average, the proportion extended over the surface decreases with siphon size. However, among the animals with a short siphon, those with a good body condition take no risks and live as deeply as possible. A comparison between species reveals that the weight of the extended inhalant siphon per cm amounts, on average, to 0.6% of the total body weight.

Depuration effects on trace metals in Anomalocardia brasiliana (Gmelin, 1791)

Bivalves have been regarded as suitable bioindicators of metal pollution in the marine and estuarine environments. However, the metal concentrations of the soft parts of individual bivalves can vary considerably depending on size variations, geographic and genetic differences, individual variability in metal uptake, ingestion of sediment particles and induction of metal-binding proteins. Metal-containing particulate matter in the gut can also be significant. These authors showed that if deputation is not carried out, then large variations in metal concentrations are more likely to occur. In the Todos os Santos Bay on the northeastern coast of Brazil, the cockle A. brasiliana is the most abundant bivalve and is well adapted to area conditions. An important source of food for many local communities, this species has been frequently used as an indicator for heavy metals pollution; however, no data have been published on metal concentrations of A. brasiliana of different size classes and on the effects of deputation on overall concentration. It is therefore important to determine the metal concentrations in A. brasiliana both from the point of view of how the concentrations relate to metal loading of the area. The effect of size upon metal concentration of shellfish has been examined bymore » Boyden, who found that zinc in Mytilus edulis was greater in smaller individuals while cadmium was independent of size. The objective of this study was to determine concentrations of copper, zinc, cadmium and lead in A. brasiliana collected from a site with a relatively low impact of heavy metal contamination, to examine metals in different size classes and to assess the effect of depuration on tissue concentration of the metals. These elements were selected due to their toxicity to marine organisms, when their excess as free metal may interact with cell structures and/or enzymes affecting metabolic activities. 22 refs., 2 figs., 2 tabs.« less

The detection of chronic biological effects in the marine intertidal bivalve cerastoderma edule, in model ecosystem studies with pulverised fuel ash: reproduction and histopathology

The cockle Cerastoderma edule was exposed to sediments variously comprised of pulverised fuel ash (PFA) for two consecutive periods of 3 and 9 months. Chronic effects of PFA on this filter feeding bivalve were studied by examining changes in cellular and tissue pathology with the aid of a screening procedure developed for analysing histopathology conditional. The mortality rate was high, up 43% for the 100% PFA sediment and growth of the individual bivalves was low. The accumulation of metals appeared to be low at 1–10 times background tissue levels. Signs of cellular stress were seen in the digestive gland after the first 3 months. However, after 9 months, this same organ was in fairly good condition. Reproduction was delayed due to slow oocyte maturation.