A 13C/12C Comparison of Food Webs in Caribbean Seagrass Meadows and Coral Reefs

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Stable carbon isotope analyses of more than 140 plant, animal, and sediment samples from the Miskito Banks, Nicaragua and St. Croix, U.S. Virgin Islands, were used to assess carbon flow in Caribbean seagrass meadows and coral reefs. Plants at the base of food webs had widely divergent δ 13C values, ranging from -4.0 (Syringodium filiforme Kütz) to -34.7% (an unidentified red alga). Isotopic values of 13 of 35 algal species ranged from -8.8 to -15.0%, and were similar to the -9.9 to -13.2% values of the dominant Caribbean seagrass, Thalassia testudinum Banks ex Koenig. This isotopic similarity prevented a clear assessment of the role that Thalassia plays in supporting Caribbean food webs. However, a 4-6% 13C enrichment was found among fish from seagrass meadows and coral reefs vs. fish collected offshore. This enrichment indicated that benthic algae and seagrasses together contribute at least 48-76% of the carbon found in fish from the former, shallow-water habitats.

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Aquatic Botany, v. 14, p. 389-398