Nyctemeral variations of magnesium intake in the calcitic layer of a Chilean mollusk shell (Concholepas concholepas, Gastropoda)

Abstract

International audienceMollusk shells are increasingly used as records of past environmental conditions, particularly for sea-surface temperature (SST) reconstructions. Many recent studies tackled SST (and/or sea-surface salinity) tracers through variations in the elementary (Mg and Sr) or stable isotope (δ¹⁸ O) composition within mollusk shells. But such attempts, which sometimes include calibration studies on modern specimens, are not always conclusive. We present here a series of Mg and Sr analyses in the calcitic layer of Concholepas concholepas(Muricidae, Gastropoda) with a very high time-resolution on a time window covering about 1 and a half month of shell formation, performed by Laser Ablation Inductively-Coupled Plasma Mass Spectrometry (LA-ICP-MS) and electron probe micro-analysis (EPMA). The selected specimen of this common Chilean gastropod was grown under controlled environmental conditions and precise weekly time-marks were imprinted in the shell with calcein staining. Strontium variations in the shell are too limited to be interpreted in terms of environmental parameter changes. In contrast, Mg incorporation into the shell and growth rate appear to change systematically between night and day. During the day, Mg is incorporated at a higher rate than at night and this intake seems positively correlated with water temperature. The nightly reduced Mg incorporation is seemingly related to metabolically controlled processes, formation of organic-rich shell increments and nocturnal feeding activity of the animals. The nyctemeral Mg changes in the C. concholepas shell revealed in this study might explain at least part of the discrepancies observed in previous studies on the use of Mg as a SST proxy in mollusk shells. In the case of C. concholepas, Mg cannot be used straightforwardly as a SST proxy

Effect of organic matrices on the determination of the trace element chemistry (Mg, Sr, Mg/Ca, Sr/Ca) of aragonitic bivalve shells (<i>Arctica islandica</i>)&mdash;Comparison of ICP-OES and LA-ICP-MS data

“…Mg/Ca ratios of some calcitic (Dodd, 1965;Lorens and Bender, 1977;Freitas et al, 2005;Lorrain et al, 2005;Lazareth et al, 2007) and aragonitic bivalve shells (Takesue and van Geen, 2004) are lower than predicted by thermodynamics. Shell Mg/Ca and Sr/Ca ratios can also vary contradictorily among different species and even among conspecific and contemporaneous specimens from one locality (corals: Cardinal et al, 2001;brachiopods: England et al, 2007;bivalves: Dodd, 1965;Gillikin et al, 2005a;Lorrain et al, 2005;Freitas et al, 2008).…”

Variability in diel and seasonal in situ metabolism of the tropical gastropod Tectus niloticus

“…Sclerochronology is analogous to dendrochronology for trees, that is, it uses information provided by the skeleton of aquatic organisms to reconstruct records of environmental and climatic change through space and time, based on growth patterns observed at various temporal scales (see Gröcke & Gillikin 2008). As an example, Lazareth et al (2007) explained night and day differences in the magnesium content (a seawater temperature proxy) in the shell of the gastropod Concholepas concholepas by the nocturnal feeding activity of the species. Schwartzmann et al (2011) also provided an instructive example of the benefits of coupling growth rate and animal behaviour studies with the giant clam Hippopus hippopus in New Caledonia.…”

Use of Stable Isotopes to Understand Food Webs and Ecosystem Functioning in Estuaries

“…Therefore, they have the potential of storing information about estuarine conditions throughout the time in which they grew. Bivalves, on the other hand, can offer snapshots of several years at very high temporal resolution (daily and even sub-daily; e.g., Wurster and Patterson, 2001;Lazareth et al, 2007) because they exhibit very high growth rates and thereby provide adequate material to sample at high resolution. Foraminifera and Ostracoda are generally short lived, but can be sampled from sediment cores and provide data on past conditions, with timescales ranging from 10 7 to 10 2 years, with decadal or even annual resolution (e.g., Ingram and Sloan, 1992, Cronin et al, 2002a, 2002b, but not usually with seasonal resolution.…”