Abstract
We determined the source of fatty acids in scleractinian corals by separately measuring and comparing the δ 13 C values of fatty acids in zooxanthellae and coral hosts from two scleractinian coral species ( Montastraea faveolata and Porites astreoides ) from reefs of the Florida Reef Tract. Using an isotopic mass balance approach, we show that zooxanthellae are the dominant source of fatty acids and that in many colonies heterotrophic feeding can be an important and significant source of essential ω 3 fatty acids for corals. There is considerable variability in feeding behavior within species, between species, and within single reef sites. In individual colonies, essential ω 3 fatty acids and energy resources such as triglycerides can be acquired from separate dietary sources, showing the importance of resource partitioning within the coral animal. Consistently, individual coral colonies acquire most of their energy‐rich saturated fatty acids from their symbiotic zooxanthellae. The particular feeding mode by which corals acquire their fatty acids appears to be specific to each coral colony. The ability of corals to modulate their feeding modes under different environments may provide an adaptive mechanism to sustain growth under stressful conditions.