Healthy White Coral: Who Knew?

The following article from The New York Times talks about the Leptoseris troglodyta, an unusual coral.

Over a decade ago, the coral researcher Bert Hoeksema found himself crossing from sunlit waters into an underwater cave in the Philippines. It was “like a big hole in a steep wall,” he said.

Leptoseris troglodyta, a coral found on the ceilings
of caves near tropical reefs in the Indo-Pacific region.

Wielding a camera and a diving light in the darkness, he looked up and saw strange clusters of white, delicate fungi-shaped polyps, like the ghosts of corals, carpeting the ceiling.
 
Most scientists associate that white hue with coral death, but this species was very much alive — and heretofore undiscovered.

“By being active in the field, we bump into new species by accident,” Dr. Hoeksema, a researcher with the Naturalis Biodiversity Center at the University of Leiden in the Netherlands, said in an interview. “It’s very thrilling.”

Twelve years later, his study of the albino coral has been published in the journal ZooKeys. The species, Leptoseris troglodyta (in Greek, troglodyta means “one who dwells in holes”), is known for inhabiting waters up to 35 meters (115 feet) deep, where the sunlight may be weaker and the ocean cooler, Dr. Hoeksema said.

What sets the species apart from other corals is the absence of zooxanthellae, a photosynthesizing algae that delivers nutrients. Such algae are also responsible for the bold swaths of color that characterize stony corals.

“The idea of white corals is not unknown at all,” Dr. Hoeksema said, referring to the bleaching events that increasingly cripple reefs. Decimated by waters that are uncomfortably warm, algae frequently undergo a mass exodus that drives the bleaching phenomenon.

Yet the whiteness of the new species is an anomaly, Dr. Hoeksema said, because it occurs naturally.
The lack of nurturing algae has left him flummoxed about how the species feeds. “Their only option is to catch food with their tentacles — they are very small, so I have no idea how they do that,” he said.

Dr. Hoeksema said that circulating particles of food cannot exactly drop onto a ceiling, which makes it harder for stationary creatures to gather nutrients. He speculates that some plankton bump into the corals. This inefficient method of feeding could account for the coral’s diminutive size – which in turn probably explains how it can colonize ceiling spaces where other, larger cave creatures cannot fit.

Since his discovery in 1999, Dr. Hoeksema has found the pale polyps on the ceilings of other Indo-Pacific caves and has established that Leptoseris troglodyta dwells across a region that overlies parts of the Coral Triangle, a mecca for marine researchers. It is host to over 70 percent of the world’s coral species and includes the waters of Indonesia, Malaysia, the Philippines, Papua New Guinea, Timor Leste and the Solomon Islands.

With that level of coral density, it is perhaps unsurprising that new species are periodically found. “We keep finding new species by going to remote areas or remote habitats that are not investigated,” Dr. Hoeksema said, noting that he recently discovered another coral in New Caledonia.
His goal is mapping biodiversity. After all, he said, you have to be familiar with the vast array of corals to recognize the paler, seemingly insignificant ones like Leptoseris troglodyta as something exciting and new.

One might think that the cave-dwelling coral’s ability to survive without algae and sunlight offers some hope for the future of coral reefs on a warming planet. But without photosynthesis and zooxanthellae, corals will not grow quickly or gain significant mass, Dr. Hoeksema said.
The discovery is valuable from a different standpoint, he said — the development of undersea life. “This is an evolutionary novelty,” he said.