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

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