MEPS 147:105-115 (1997)  -  doi:10.3354/meps147105

Temporal variation of delta13C in particulate organic matter and oyster Crassostrea gigas in Marennes-Oléron Bay (France): effect of freshwater inflow

Riera P, Richard P

The temporal variability of delta13C in suspended particulate organic matter (POM) and oyster Crassostrea gigas along a salinity gradient was investigated from May 1992 to September 1993 within the estuarine bay of Marennes-Oléron (France). During this period the mean daily discharge of the Charente River exhibited large seasonal variation, with a high discharge from November 1992 to January 1993. Contrary to that at the river mouth and the marine littoral, delta13C in POM and in oysters at mid-estuary was affected by the high flood period. The delta13C values of POM decreased in mid-estuary and remained at low levels during the high discharge period, indicating an increasing contribution of terrestrial inputs to the estuarine POM pool. At the same site, a remarkable decrease of delta13C in oysters occurred between December 1992 and March 1993 (after a time lag compared to the ambient POM), indicating incorporation of terrestrial organic matter in oyster tissues during the high flood discharge. The lag between the delta13C decrease in POM and oysters is attributed to the time needed for oyster tissues to incorporate enough newly terrestrial light carbon to be recognized by the delta13C measure (about 1 to 2 mo). This time interval depends on tissue turnover time. The delta13C POM decrease (i.e. 1.3o/oo) cannot explain entirely the decrease observed in oysters (i.e. 2.3o/oo). In fact, the pattern exhibited by mid-estuarine oysters can be explained by the increasing contribution of terrestrial organic matter to their feeding, and the inability to preferentially utilize specific components of the estuarine POM that are 13C-enriched.

Temporal variation · Carbon isotope ratio · Crassostrea gigas · Particulate organic matter · Freshwater inflow

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