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Surprise! Algae Found in Coral at Record-Breaking Depths
Black corals still remain mysterious. This latest finding only adds to the mystery.
Credit: Daniel Wagner, HIMB/SOEST/UHM.

Coral with algae in its tissues has been discovered at never-before-seen depths.

The record-setting black coral, a type of deep-dwelling, branching coral, was found to live 1,300 feet (396 meters) below the surface of the ocean.

"The deepest record for these algae was just over 600 feet (83 meters), doubling the previous deepest record for these organisms," said Daniel Wagner, a Ph.D. candidate at the University of Hawaii, and lead researcher of a study of the coral that will appear in an upcoming issue of the journal Proceedings of the Royal Society B.

Scientists looked at 14 different species of black coral from around Hawaii, and found that a surprising 71 percent of them harbored algae cells.

Algae are found in nearly all reef-building corals the best-known type of corals, which live from near the surface of the sea down to around 130 feet (40 meters). But their presence in black coral, which can live in very shallow seas all the way to depths of tens of thousands of feet, was unexpected, Wagner told OurAmazingPlanet.

Corals that live close to the surface, where sunlight is plentiful, use the algae that live in their tissues as tiny snack-makers. The algae photosynthesize, and the coral feed on the nutrients produced by the process.

Why would these deep-dwelling coral play host to algae? Researchers don't know.
Why would these deep-dwelling coral play host to algae? Researchers don't know.
Credit: Daniel Wagner, HIMB/SOEST/UHM.

Since most black coral live at depths beyond the reach of much sunlight, and even of scuba gear, Wagner said, "It was generally assumed that most black corals didn't have the algae that are found in many shallow water corals."

Much of even the basic biology of black coral remains mysterious, and this new discovery has merely added to the mystery.

Wagner said the distribution of algal cells in the black coral was of a lower density than in species that live in shallower waters. And he emphasized it's too early to say what function the algae serve in the deep-dwelling species .

Wagner and his collaborators are planning an expedition in January 2011 to collect more samples and conduct further study on the black coral that live in the deep ocean off the Hawaii archipelago.