Trophic typology of coastal ecosystems based on δ13C and δ15N ratios in an opportunistic suspension feeder

Abstract

Our objective was to use stable carbon (C) and nitrogen (N) isotope ratios of the adductor muscles of cultured Crassostrea gigas to typify the trophic state of temperate coastal ecosystems. Young oysters were introduced on a regional geographical scale in 8 locations along the coast of Normandy (France) and sampled after 9 mo in cultivation. Food sources were also investigated using a mixing model based on food source isotopic composition data previously obtained. To strengthen the interpretation of trophic ecosystem functioning, values of stable isotope ratios were combined with environmental variables in a principal component analysis (PCA). Isotopic values of adductor muscles varied significantly between -19.94 and -17.26 ‰ for δ 13 C and between 7.73 and 12.14 ‰ for δ 15 N. PCA discriminated 2 groups of coastal ecosystems that differed in coastal hydrology, inputs of nutrients, and size of their respective watersheds. Our results suggest that isotopic signature differences between these 2 spatial groups appeared too important to be due to (1) variations in the isotopic ratios of food sources and (2) differing trophic step fractionation between locations. These differences are more probably linked with differences in oyster diets. Finally, we conclude that cultured C. gigas is a useful spatial bio-indicator of coastal ecosystem trophic functioning in temperate ecosystems and an interesting biological model for the determination of isotopic baselines.

Modelling the spatial heterogeneity of ecological processes in an intertidal estuarine bay: dynamic interactions between bivalves and phytoplankton

“…Wild cockles Cerastoderma edule are found in the southern and the western parts of the bay in quantities estimated at 1000 and 1500 t, respectively. Freshwater enters the southern part of the bay from 4 rivers that drain a watershed area of ~3465 km 2 (Lefebvre et al 2009). The total mean discharge is ~53 m 3 s -1 (ranging from 2.2 m 3 s -1 at the lowest water level to 400 m 3 s -1 during floods).…”

The Comparison of δ13C Values of a Deposit- and a Suspension-Feeder Bio-Indicates Benthic vs. Pelagic Couplings and Trophic Status in Contrasted Coastal Ecosystems

“…Two other sites, Lestre (LES) (49°33′ N, 01°18′ W) and Baie des Veys (BDV) (49°23′ N, 01°08′ W) are located on the east coast of the Cotentin peninsula (south-western Baie de Seine in the English Channel) which are under residual south-north current and with a macrotidal regime with a 8-m maximum tidal amplitude. Their trophic status is eutrophic (Lefebvre et al 2009a;Grangeré et al 2012). LES receives freshwater runoff from a small river (Sinope) which drains a watershed area of 197 km 2 (Fig.…”

“…Two sites Lingreville-sur-mer (LIN) (48°57′ N, 01°34′ W) and Saint Germain (SG) (49°14′ N, 01°39′ W), are located on the west coast of the Cotentin peninsula whose intertidal area is characterized by a megatidal regime with a 14-m maximum tidal amplitude and direct exposure to the prevailing west wind. It is directly open to the English Channel and exhibits a high marine influence and their trophic status is mesotrophic (Lefebvre et al 2009a;Grangeré et al 2012). Terrestrial inputs to both sites come from three main rivers (Ay, Soulle and Sienne) with a flow ranging from 2.2-24.3 m 3 s −1 and a total watershed area of 929 km 2 (Fig.…”

“…δ 13 C and δ 15 N values of long-lived (between 2 to 5 years) benthic primary consumers such as suspension-feeder bivalves with moderate tissue turnover rates (weeks to months depending on the tissue) were shown to be adequate to assess the planktonic compartment (Gustafson et al 2007;Fukumori et al 2008;Lefebvre et al 2009a;Grangeré et al 2012). The strict suspension-feeder C. gigas (Thunberg 1793) lives at the sediment-water interface which makes them a useful bioindicator of the POM benthic-pelagic coupling.…”

“…(Fertig et al 2009) were suggested to monitor the anthropogenic impact or animal wastes on watershed in aquatic ecosystems. Lefebvre et al (2009a) and Grangeré et al (2012) suggested the use of both δ 13 C and δ 15 N values of the Pacific oyster C. gigas muscle tissue to typify the trophic functioning of coastal ecosystems.…”