Spatial Variability of Stable Isotope Ratios in Oysters (Crassostrea gigas) and Primary Producers Along an Estuarine Gradient (Bay of Brest, France)

Abstract

Nerot, et al.. Spatial variability of stable isotope ratios in oysters (Crassostrea gigas) and primary producers along an estuarine gradient (Bay of Brest, France). AbstractThis study aimed at characterizing the diet of the oyster Crassostrea gigas along an estuarine gradient in the Bay of Brest (France), through stable isotope (δ 13 C and δ 15 N) measurements in primary producers and wild oysters. The contribution of different potential food sources to the diet of C. gigas was estimated at high spatial resolution (over a gradient of 40 km with samplings every 2 km) to identify ecological transition zones, and highlighted the dominance of resuspended biofilm in oysters diet. Although the different primary producers did not display any obvious pattern along the estuarine gradient, the stable isotope signatures of C. gigas differed among estuarine, inner Bay and open sea sites.In particular, a striking 15 N depletion pattern was found along the gradient which allowed to identify seven homogeneous groups. Moreover, some unexpected values found at two stations within the estuary revealed localized anthropogenic disturbances. Overall, our results suggest that suspension-feeders might be better indicators of ecosystem functioning than primary producers, and reflect the different ecological processes occurring along estuarine gradients, including localized anthropogenic inputs. We suggest that the usefulness of suspension-feeders as indicators of ecosystem functional typology lies in the dominance of benthic material in their diet, which results in locally occurring processes being reflected in oysters' stable isotope ratios.KEY WORDS: biofilm -carbon -nitrogen -food web -estuary -Bay of Brest 2

Stable isotope analysis suggests the existence of multiple populations of streaked spinefoot (Siganus javus L.) in Bandon Bay, Southern Thailand

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Ecological impacts of non-native Pacific oysters (Crassostrea gigas) and management measures for protected areas in Europe

“…Field investigations of the impact of extensive cultivated C. gigas on chlorophyll concentrations in Wallapa Bay, USA, supported modelled scenarios and showed that although oyster filtration rates were lower than laboratory measurements, the oysters can exert top-down control on phytoplankton production within estuaries (Wheat and Ruesink 2013). Yet isotopic analysis on the diet of wild Pacific oysters on rocky shores along an estuarine gradient in the Bay of Brest (Marchais et al 2013) found that benthic biofilms and resuspended macro algal detritus, rather than phytoplankton, constituted the greatest proportion of the diet. The 1 m height difference between oysters cultivated on trestles and benthic wild oysters may explain variance in the proportion of benthic v pelagic sources (Marchais et al 2013), so caution is necessary at extrapolating impacts of aquaculture to the issue of wild settlement.…”

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Comparative study of isotopic trends in two coastal ecosystems of North Biscay: A multitrophic spatial gradient approach

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