Dynamics and sources of suspended particulate organic matter in the Marennes-Oléron oyster farming bay: Insights from stable isotopes and microalgae ecology

The aim of this study was to distinguish between sources of the complex variety of Marennes-Ole´ron Bay suspended particulate organic matter (SPOM) contributing to the tropho-dynamics of the Marennes-Ole´ron oyster farming bay. Basic biomarkers (Chl a, C/N and POC/ Chl a ratios), carbon and nitrogen stable isotopes from SPOM were analyzed and the microalgae community was characterized. The sampling strategy was bimonthly from March 2002 to December 2003; samples were taken from an intertidal mudflat. Four main sources contributed to the SPOM pool: terrigenous input from rivers, neritic phytoplankton, resuspended microphytobenthos and periodic inputs from intertidal Zostera noltii meadows. Seasonal fluctuations were observed in both years of the study period: (1) SPOM collected in the spring of 2002 (d13C¼ 25& to 23&) was mainly composed of fresh estuarine inputs; (2) SPOM from the summer and fall of 2002 and 2003 was predominantly neritic phytoplankton (d13C¼ 22& to 19&); (3) SPOM from the winter of 2002, spring of 2003 and winter of 2003 (d13C¼ 21 to 23&) was composed of a mixture of decayed terrigenous river inputs and pelagic phytoplankton, which was predominantly resuspended microphytobenthos. In the summer of 2003dthe warmest summer on record in southern France and EuropedSPOM was particularly enriched for 13C, with d13C values ranging from 14& to 12&. Pulses in d13C values, indicative of 13C-enriched decaying materials, extended into the fall. These were attributed to benthic intertidal inputs, including both resuspended microphytobenthos and Z. noltii detritus. Changes in SPOM sources in Marennes-Ole´ron Bay may lead to differences in the quality of the trophic environment available for reared oysters. 2007 Elsevier Ltd. All rights reserved.