for National Geographic News
Soft coral communities in tropical waters may literally be melting away because of bleaching events, which have been dramatically accelerated by global warming, a leading expert says.
Unlike their hard coral cousins, soft corals have no stony outer skeletons to leave behind when they die. Instead their fleshy branches extend uncovered from reefs, where they grow alongside hard corals.
This means that soft corals simply vanish in response to environmental stresses.
"I have observed sites before and after bleaching in Okinawa, Japan, and it was remarkable to see a massive disappearance of soft corals," said marine biologist Hudi Benayahu, head of the Porter School of Environmental Studies at Tel Aviv University.
"You can't imagine this was the same site. Just two years passed and the entire area was deserted, lifeless."
Soft corals are common throughout the Indo-Pacific Ocean, where Benayahu focuses his research. But efforts to cataloge the world's soft corals are still underway, and many species remain unknown to scientists.
Benayahu and other experts say that if bleaching continues to intensify, entire soft coral species may go extinct before they are even discovered.
The causes of coral bleaching are roughly the same for hard and soft corals.
Slight changes in water temperature or salinity can damage the mutually beneficial relationship between coral and the algae—called zooxanthellae—that live in their tissues.
Such stresses cause the algae to "jump ship," and without them the corals eventually die. In hard corals, the loss of living animals inside the exoskeletons causes once colorful reefs to appear stark white.
(See related photos of healthy coral reefs.)
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