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Whether aquatic animals rely primarily for sustenance upon vascular macrophytes or attached algae has been often debated. A compilation of carbon isotope data from the literature for coastal seagrass meadows, estuarine salt marshes, and freshwater lakes and rivers indicates that animal δ¹³C values more closely approximate those of attached algae than they do those of vascular plants. This empirical synthesis supports results from individual studies in suggesting that macrophytes are unlikely to play an exclusive and direct dietary role in aquatic foodwebs.