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Coral Bleaching Teaches Lessons on Restoration Techniques

From late summer to early fall 2014, there was a coral bleaching event in South Florida. Bleaching is a major threat to coral reefs. NOAA is using what we’ve learned from this event to recover and restore other vulnerable coral populations.

What is Coral Bleaching?
When corals are stressed by changes in conditions such as temperature, light, or nutrients, they expel the symbiotic algae that live in their tissues. This causes them to turn completely white—hence the term “bleaching.” Elevated water temperatures are most often the cause of bleaching events, although they can also be caused by cold water and other factors.

Corals can survive a bleaching event, but they often die when the stressful conditions continue for an extended period.

What Happened in South Florida?
Due to elevated water temperatures, corals were bleached in the Florida Keys between August and October 2014. Bleaching was worst in the Lower Keys and Key West, while areas to the north were less affected. Upwards of 70 percent of some coral species died after bleaching in the affected areas, including threatened elkhorn and staghorn corals.

What Did We Learn?
We work on coral recovery and restoration in Florida by growing corals in nurseries for transplanting to natural reefs. Our partners observed which coral strains (both in the nurseries and reefs) were most affected by the bleaching. This allowed us to document which corals better tolerate stressful conditions.

This information will be valuable for future efforts to recover populations of these important corals. Knowing which corals are most likely to survive bleaching events, we’ll be sure to use them in our efforts to restore coral reefs.

Posted February 19, 2015

A bleached elkhorn coral colony in the Florida Keys. (above)

Elkhorn coral colonies in a coral nursery. The white corals in the center are fully bleached while the ones on the right are partially bleached.(below)