CRITTER: Meet the coral that looks like snow

Scuba diving one day years ago on the outer reefs at Sharks Cove on O‘ahu’s North Shore, I found an overhang where the big winter surf had carved out a large finger of lava from a cliff that sticks out about 30 feet. This unusual looking reef looks like your closed fist with one finger pointing straight out.

I decided to see if anything was growing on the underside of this dark lava finger, so I turned on my bright dive video lights to check it out. As soon as I went under the overhang I looked up and was stunned with what I saw. The entire surface of the rock was covered in what looked like thousands of pure-white, 4-inch-tall Christmas trees! It was just stunning to see this unusual coral for the first time, especially in a place where 30-foot waves break in the winter!

The coral I was looking at turned out to be snowflake coral that usually grows in Indonesia, not Hawai‘i. After doing some research I found out that this coral species was not even seen in Hawai‘i until 1972, so it was never given a Hawaiian name. We think the coral may have come to Hawai‘i on the hull of a boat and then spread around the islands over the years.

Snowflake coral only grows in dark caves and overhangs where the sunlight does not reach. It grows down from the roof of the caves and forms a calcium carbonate structure that is orange in color and fairly rigid. White coral polyps grow out from the orange skeleton, and when they are out filter feeding on plankton the coral is pure white. But when the polys are retracted the coral is orange.

Most stony corals live in shallow water on top of the reef, where they are in the sunshine. The coral polyps in corals like cauliflower and antler corals grow algae in their tissue, which gives the coral its color.

The snowflake coral grows in the dark, so it does not have algae in the polyp tissue and is pure white. The orange color of the coral skeleton comes from dissolved minerals in the seawater.

Snowflake coral colonies are very beautiful, and most divers never get to see them because they grow in areas of high surf and current. The only problem with these corals is they grow in the same habitat as our famous black coral that is well known for making jewelry. The snowflake coral seems to be more aggressive, and is killing off much of our very rare black coral.

You can see the snowflake coral in action in my documentary movie I produced about the marine life at Sharks Cove on O‘ahu up on my webpage at underwater2web.com.

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Terry Lilley is a marine biologist living in Hanalei. He is co-founder of Reef Guardians Hawai‘i, a nonprofit on a mission to provide education and resources to protect the coral reef. To donate to Reef Guardians Hawai‘i go to www.reefguardianshawaii.org.