Experimental shift of diet and DIC stable and carbon isotopes: Influence on shell delta C-13 values in the Manila clam Rudipates philippinarum

The influences of diet and seawater dissolved inorganic carbon (DIC) on the carbon isotope
composition of shell aragonite (?
13Cshell) in the Manila clam Ruditapes philippinarum reared under
laboratory conditions were investigated. Clams were exposed to two successive negative carbon
isotope shifts: a first shift in diet (?
13Cphytoplankton) and a second shift, 35 days later, in DIC (?
13CDIC).
Both successive shifts induced a decrease in ?
13Cshell. These results are the first to experimentally
confirm an incorporation of respired carbon derived from food and carbon from DIC into shell
carbonate of adult bivalves. Skeletal ?
13C responded to changes in the ?
13C of both diet and DIC in
less than 7 days. Consequently, proxies based on ?
13Cshell may be used with high temporal resolution.
Using ?
13Cphytoplankton as a proxy for the carbon isotope composition of respired carbon (?
13CR) resulted
in a rather constant percentage of metabolic carbon (CM) into the shell carbonate over time (close to
12%). However, an accurate estimation of ?
13CR is required in order to precisely estimate the
percentage of metabolic carbon incorporated into the shell. Despite the significant incorporation of
metabolic carbon into shell carbonate, our experimental results revealed that ?
13Cshell was highly
correlated with ?
13CDIC (r² = 0.77, p <0.0001). Thus it seems that ?
13Cshell is a promising proxy of large
scale variations in ?
13CDIC and therefore of salinity in estuarine water.

Publication year:2010

Keywords:metabolic carbon