Coupling experimental and field-based approaches to decipher carbon sources in the shell of the great scallop, Pecten maximus (L.)
Résumé
This research investigated how the carbon isotopic composition of food source (d13Cfood) and dissolved inorganic carbon
(d13CDIC) influences the carbon isotopic composition of Pecten maximus shells (d13Cshell) under both experimental and natural
conditions. The objectives are to better understand the relationship between P. maximus and its environment, and to specifically
distinguish conditions under which calcification is influenced by respired CO2 derived from food sources versus conditions in
which calcification uses inorganic carbon from seawater. Laboratory experiment investigated carbon incorporation into shell
carbonates by maintaining scallops under conditions where the stable carbon isotopic composition of food sources was considerably
depleted (-54 per mille), relative to values observed in the natural environment (-21 per mille). Laboratory experiment ran for 78 days
under three temperature conditions, 15 °C, 21 °C and 25 °C. A survey of the environmental parameters and stable carbon isotopic
composition into shell carbonate of natural population of P. maximus was also realized during the same year in the Bay of
Brest, France. Data collected from both laboratory experiment and the natural environment confirmed that both d13CDIC and
d13Cfood influence d13Cshell values and that organic carbon incorporation (CM) averages about 10% (4.3–6.8% under experimental
conditions and 1.9–16.6% in the natural environment). The shift in stable carbon isotopic composition from the uptake of
depleted food sources under experimental conditions realized a marked divergence in the predicted equilibrium between calcium
carbonate and ambient bicarbonate, relative to the natural environment. This offset was 1.7 ± 0.6 per mille for scallops in their natural
environment and 2.5 ± 0.5 and 3.2 ± 0.9 per mille for scallops under experimental conditions at water temperatures of 15 °Cand 21 °C,
respectively. The offset of 3 per mille for scallops subjected to laboratory experiment could not be explained in light of growth rate but
may be related to food supply and/or temperature. Food source and temperature effects may also explain the annual variation
observed in CM values measured from scallops in their natural environment. CM estimation from the natural population of
P. maximus varied seasonally from around 2% at the end of winter, to 12% in summer. The seasonal variation resembles
variability in the carbon isotopic composition of the food sources throughout the year with an exception at the end of winter.
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