What was done
Two experiments examined the effects of short-term sediment burial on four southeast Asian corals.  In the first experiment, Porites corals growing at a depth of 2 meters were subjected to full sediment burial for periods of 6, 20, and 68 hours.  The second experiment involved three other corals in addition to Porites, all of which were also exposed to full sediment burial for periods of 6, 20, and 68 hours, but at a depth of 5 meters.

What was learned
In the first experiment, Porites corals endured the 6-hour sediment exposure quite well, but the longer period sediment treatments fared worse; increased discoloration was noted in corals buried for 20 hours, and up to 90% of their tissue bleached in the first days after the 68-hour treatment.  The bleached corals, however, experienced considerable recovery 3 to 4 weeks later.  At the 5-meter depth, complete coral mortality was observed in one taxa, Acropora, for all sediment burial time lengths.  The other corals treated at this depth responded similarly to the 2-meter experiment with Porites.

What it means
Sedimentation has been cited as one of the "main destructive forces for coral reefs."  It can result from terrestrial deforestation, marine construction and dredging, heavy river discharge and intense rainfall events.  This study adds to the growing list of literature documenting coral reef bleaching to be one of the more severe responses of corals to sediment deposition.  Although some species of corals, such as Acropora, may experience total mortality under heavy sediment burial, as indicated here, others are less affected and experience full recovery after the stress is removed.