Clams as Bioindicators of Seasonal and Spatial Variability of Riverine Inputs to Estuarine Food Webs

Résumé fourni par la source

Abstract Changing rainfall patterns driven by climate change are altering the seasonal delivery of organic matter from rivers to estuaries, with consequences for food-web dynamics in many regions worldwide. The importance of riverine subsidies to estuarine food webs is poorly understood, particularly at a high spatial resolution (1–2 km). This study provides a high-resolution assessment of seasonal (summer and winter) variation in riverine contributions to the diets of clams ( Katelysia spp. ) within a temperate estuary in southern Australia. We examined a simplified food web, using stable carbon and nitrogen isotopes to measure and evaluate clam gill tissue (ctenidia), particulate organic matter from riverine, estuarine, coastal and benthic sources (< 200 μm), and seasonal macroalgae. The summer food web was compartmentalized, with riverine resources estimated to comprise 8.4 to 18.0% of clam diets. Clam diets at sites with greater riverine influence included comparatively more rPOM. The stable isotope signatures of the food sources in winter were less distinct, preventing the use of mixing models to estimate clam diets. The winter decline in δ 13 C for clams at two sites, indicates greater reliance on riverine organic matter and reveals pronounced spatial heterogeneity in resource use at fine spatial scales. These results suggest that clam gill tissue may be a useful indicator for resolving high-resolution seasonal food web isoscapes. These findings highlight the importance of incorporating fine-scale ecosystem features, including creeks and small tributaries, into the design and interpretation of estuarine food-web studies, given that such localized inputs emerge more clearly at higher spatial resolutions.

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