Reef building corals are generally believed to require clear, nutrient-poor
water. Yet, paradoxically, coral reefs are among the most productive marin
e ecosystems in the world. This paradox is commonly explained by the coral'
s ability to utilize a number of food resources, including zooplankton, phy
toplankton, dissolved organic matter and photosynthetic products derived fr
om their endosymbiotic algae, the zooxanthellae. Sedimentation is a known s
tressor for corals, inhibiting most feeding modes in various ways. However,
evidence for enhanced sediment deposition on certain corals, induced by th
eir morphologies, as well as for sediment ingestion by some corals, has led
us to examine the use of sediment as a possible source of food for corals
in addition to the other, known food sources. Our experiments with fluoresc
ently labelled sediment show transfer of labelled organic matter from the s
ediment into the cells of the solitary coral Fungia horrida Dana 1846. The
results provide the first direct evidence for the ability of a coral to dig
est the sediment's organic fraction. These results may indicate a positive
role of sediment, which up until now was considered to have only deleteriou
s effects on corals.