16 research outputs found
Modification of Ca isotope and trace metal composition of the major matrices involved in shell formation of Mytilus edulis
In this study we present the first combined investigation into the composition of the major matrices
involved in calcification processes (surrounding water, extrapallial fluid, aragonite, and calcite) of Mytilus
edulis with respect to their calcium isotope (d44/40Ca) and elemental compositions (Sr/Ca and Mg/Ca). Our
aim was to examine the suitability of Mytilus edulis as a proxy archive and to contribute to the
understanding of the process of biomineralization. Mytilus edulis specimens were live collected from the
Schwentine Estuary, Kiel Fjord, and North Sea (Sylt). d44/40Ca was determined by thermal ionization mass
spectrometry (TIMS) accompanied by measurements of Mg/Ca and Sr/Ca using inductively coupled
plasma–optical emission spectroscopy (ICP-OES). The elemental and isotopic compositions of the
investigated matrices showed systematic offsets. The carbonates are strongly depleted in their magnesium
and strontium concentrations and fractionated toward lighter calcium isotope compositions relative to the
surrounding Schwentine Estuary water. The opposite is observed for the extrapallial fluid (EPF). Our
findings extend the results of previous studies reporting a strong biological control and the interaction of
different environmental conditions influencing biomineralization. Future studies should focus on the
temporal development of the interrelation between the different matrices
Manganese in the shell of the bivalve Mytilus edulis: Seawater Mn or physiological control?
Manganese in the shell calcite of marine bivalves has been suggested to reflect ambient seawater Mn concentrations, thus providing a high-resolution archive of past seawater Mn concentrations. However, a quantitative relationship between seawater Mn and shell Mn/Ca ratios, as well as clear understanding of which process(es) control(s) shell Mn/Ca, are still lacking. Blue mussels, Mytilus edulis, were grown in a one-year duration field experiment in the Menai Strait, U.K., to study the relationship between seawater particulate and dissolved Mn2+ concentrations and shell calcite Mn/Ca ratios. Shell Mn/Ca showed a well-defined intra-annual double-peak, with maximum values during early spring and early summer and low values during autumn and winter. Seawater particulate Mn peaked during winter and autumn, with a series of smaller peaks during spring and summer, whereas dissolved Mn2+ exhibited a marked single maximum during late-spring to early-summer, being low during the remainder of the year. Consequently, neither seawater particulate Mn nor dissolved Mn2+ concentrations explain the intra-annual variation of shell Mn/Ca ratios. A physiological control on shell Mn/Ca ratios is evident from the strong similarity and timing of the double-peaked intra-annual variations of Mn/Ca and shell growth rate (SGR), the latter corresponding to periods of increased metabolic activity (as indicated by respiration rate). It is thus likely that in M. edulis SGR influences shell Mn/Ca by altering the concentration or activity of Mn2+ within the extra-pallial fluid (EPF), by changing the flux of Mn into or the proportion of protein bound Mn within the EPF. By linking shell Mn/Ca ratios to the endogenous and environmental factors that determine growth and metabolic activity, this study helps to explain the lack of a consistent relationship between shell Mn/Ca in marine bivalve shell calcite and seawater particulate and dissolved Mn2+ concentrations. The use of Mn content from M. edulis shell calcite as a proxy for the dissolved and/or particulate Mn concentrations, and thus the biogeochemical processes that control them, remains elusive