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

Abstract

The aim of this study was to distinguish between sources of the complex variety of Marennes-Oléron Bay suspended particulate organic matter (SPOM) contributing to the tropho-dynamics of the Marennes-Oléron 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 (δ 13 C = −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 (δ 13 C = − 22‰ to −19‰); (3) SPOM from the winter of 2002, spring of 2003 and winter of 2003 (δ 13 C = −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 2003-the warmest summer on record in southern France and Europe-SPOM was particularly enriched for 13 C, with δ 13 C values ranging from −14‰ to −12‰. Pulses in δ 13 C values, indicative of 13 C-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-Oléron Bay may lead to differences in the quality of the trophic environment available for reared oysters.

Trophic importance of diatoms in an intertidal Zostera noltii seagrass bed: Evidence from stable isotope and fatty acid analyses

“…In this seagrass bed, isotope compositions of epiphytic diatoms are in the same range than those of Carlier et al (2009). For microphytobenthos, values measured in the present study are well within the range of previous observations from other seagrass beds: from -18 to -11.5‰ (Dauby, 1995;Leduc et al, 2006;Kharlamenko et al, 2008) and from bare mudflats in Marennes-Oléron Bay (Riera and Richard, 1996;Malet et al, 2008). δ 13 C values of Z. noltii roots, leaves and fresh detrital matter fractions were also similar to the values found in the literature for the same species (Boschker et al, 2000;Schaal et al, 2008).…”

“…Except in summer 2007, SPOM δ 13 C were very similar to previous measurements in the same area (Malet et al, 2008). These signatures encompasses the full range of δ 13 C between oceanic (-19.5 to -21.8‰) and estuarine SPOM values (-22.6 to -24.4‰) observed by Riera and Richard (1997) and classically encountered on an estuary-ocean continuum.…”

Interacting effects of deposit feeding and tidal resuspension on benthic microalgal community structure and spatial patterns

“…That the incoming tide homogenizes but also removes BMA biomass does, however, suggest that a significant portion of intertidal BMA production is redistributed, e.g. to the water column or deeper sediments, thereby subsidizing these adjacent ecosystems (de Jonge & van Beusekom 1992, Malet et al 2008.…”

Tracing cadmium contamination kinetics and pathways in oysters (Crassostrea gigas) by multiple stable Cd isotope spike experiments

“…at a constant level (35 ~ 10 cells oyster L , counting by Nageotte chamber) close to environmental conditions (e.g. Marennes-Ole´ron Bay, Malet et al, 2008;Thau Lagoon, Dupuy et al, 2000). Algae for trophic characterisation were 112 Cdspiked at 2 mg L -1 for 200~10 3 cells L -1 , 48 h before being fed to the oysters, and were added to the experimental treatments every two days.…”