Listed as critically endangered by IUCN, elkhorn coral
once formed the backbone of many Caribbean coral reefs. But over the past 30 years these corals they have declined by 90 percent. Warm ocean temperatures stress the corals, causing them to eject their energy-providing, color-infusing algae in an often fatal "bleaching" process.
As corals decline, they take much of the local life with them.
"Reefs are where the greatest biodiversity is in the oceans," Duke University's Pimm explained. "That is the major worry for oceanic biodiversity, and it's something that extends far beyond [U.S.] national borders across the entirety of the world's tropical oceans."
Photograph by Steve Raymer, National Geographic Stock