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The Importance of Allochthonous Subsidies to an Estuarine Food Web along a Salinity Gradient
Citation:
DIAS, E., J. HOFFMAN, P. MORAIS, A. M. COTTER, J. CAMPOS, AND C. ANTUNES. The Importance of Allochthonous Subsidies to an Estuarine Food Web along a Salinity Gradient. Presented at Coastal and Estuarine Research Federation, Daytona Beach, FL, November 06 - 10, 2011.
Impact/Purpose:
To study the contribution of autochthonous and allochthonous OM sources to primary consumers in the Minho River estuary (N-Portugal, Europe), we characterized the carbon (?13C) and nitrogen (?15N) stable isotope ratios of primary consumers (zooplankton and the invasive clam Corbicula fluminea) and their potential OM sources, as well as the concentration and stable isotope ratios of dissolved inorganic carbon (DIC) and particulate OM (POM) along the estuarine salinity gradient.
Description:
Estuarine food webs function within a heterogeneous mosaic and are supported by a mix of primary producers from both local and distant sources. Processes governing the exchange and consumption of organic matter (OM), however, are poorly understood. To study the contribution of autochthonous and allochthonous OM sources to primary consumers in the Minho River estuary (N-Portugal, Europe), we characterized the carbon (?13C) and nitrogen (?15N) stable isotope ratios of primary consumers (zooplankton and the invasive clam Corbicula fluminea) and their potential OM sources, as well as the concentration and stable isotope ratios of dissolved inorganic carbon (DIC) and particulate OM (POM) along the estuarine salinity gradient. The ?13CDIC values were lowest in the tidal freshwater (TFW) portion and higher toward the river mouth, following the expected conservative mixing. In the TFW portion, particulate organic carbon (POC) ?13CPOC values (bottom: -28.5‰ to -25.5‰; surface: - 29.3‰ to -26.3‰) and C:N (>10) of particulate samples indicated that terrestrial-derived sediment comprised a large portion of the bulk POM pool. In the polyhaline portion, ?13CPOC values (bottom: -20.5‰ to -18.8‰; surface: -25.5‰ to -23.2‰) indicated that the bulk POM pool was generally derived from phytoplankton. In the brackish estuary, zooplankton ?13C values were similar to bottom ?13CPOC values, suggesting that marine-derived OM provided a subsidy to the planktonic food web. In contrast, zooplankton ?13C values in the TFW were similar to surface and bottom ?13CPOC values, suggesting increasing importance of terrestrialderived OM. Corbicula fluminea presented a similar trend to the zooplankton in the TFW, suggesting that the benthic food web was also subsidized by terrestrial-derived OM. Our stable isotope data suggest that the Minho River estuary has a high degree of connectivity along the estuarine salinity gradient and that both marine and freshwater inputs provide a food web subsidy.