Scuba diving on an outer reef at Sharks Cove O‘ahu one day in the winter, I made a coral discovery by accident. There was some surf so no one else was out diving that day, but I was out beyond the waves in relatively calm water, and the swell was creating an underwater surge that was like being in a washing machine, but at 40 feet deep!
I was shooting video of a large ulua (jack) when I got washed back under a large, rocky ledge and briefly tumbled upside down until the surge passed by. Laying on my back with my bright video lights on, I felt like I was in a snowstorm, as the entire ceiling of the dark ledge was pure white and looked like snow falling. I said to myself, “What the heck is this stuff growing on the ledge?” I had never seen anything like it here in Hawai‘i after doing over 3,000 dives!
After some research and sending off some pictures I found out the white, five-inch-long creatures growing under the ledge are snowflake corals, and they are not native to Hawai‘i. Apparently, they showed up in Hawai‘i in the 1970s and are just growing in deep, dark underwater caves that lack much coral growth due to the lack of any sunshine.
Most hard, stony corals that grow up on top of the reef have algae that grows in the coral tissue. This algae gives the coral its color, and also produces sugars for the coral to feed on. But the algae needs sunlight to grow. The corals that grow in dark caves without sunlight have to get food by filter feeding, and they get their colors from minerals they absorb from the sea water.
This matting of snowflake corals grows straight down from the roof of the cave, and each coral is made of a hard, calcium compound that is yellow to orange in color. The small polyps (coral animals) are soft and pure white. Each one looks like a snowflake, and they are filter-feeders, eating plankton that float by. These corals have to live in a high-current area in order to filter-feed, so most divers will never see them because high-current areas in deep, dark caves or ledges are not your standard dive sites!
I was so excited to accidentally find this upside-down garden of snowflake corals that I went in to tell my dive buddy so she could come out and get some good, wide-angle pictures of this beautiful coral garden. We went back out on a calm day, but it took 30 minutes for me to relocate the ledge, as it is a long way from shore. But we finally found it, and Pamela got some amazing pictures of me under the snowy ledge to document its existence here in O‘ahu.
You can see most of Hawai‘i’s coral species in action on the underwater marine-life educational web page, underwater2web.com, and also follow my weekly worldwide marine life educational post on my Instagram at terry.lilley
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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 reefguardianshawaii.org.
