COURTESY OF SAM KAHNG
A close-up view of the snowflake coral, also known as Carijoa riisei, reveals its polyps. This alien species is threatening Hawaii's black coral industry.
An alien coral that looks like snowflakes has created a "virtual graveyard" for black coral off Maui, says Richard Grigg, University of Hawaii oceanographer and coral reef specialist.
Grigg is principal investigator for a study funded by the Sea Grant Program on Carijoa riisei, an invasive coral species believed to have been introduced to Hawaii from the Caribbean.
Sam Kahng, graduate student in oceanography, is working with Grigg, and they're submitting a proposal to expand the research because of potential economic and ecological damage.
It's of great concern to Maui and the black coral industry, valued at more than $30 million annually, Grigg said.
"Divers love it," Kahng said. "It's very beautiful, like snowflake coral when the (white) polyps are out, but quite deadly when it comes to taking over black coral."
Grigg said "it's tempting" to compare snowflake coral to the aquatic fern Salvinia molesta that blanketed Lake Wilson. "But this is a lot more subtle and complicated. It could affect parts of the reef system, shallow and deep."
The researchers want to learn the coral's life history, why and how fast it's exploding, where it will go and what can be done about it. "We may stumble on a controlling mechanism," Grigg said.
Snowflake coral is one of few soft corals in Hawaii, with tiny spicules that give the skeletons some structure but don't build reefs, the scientists said.
It was first discovered in Pearl Harbor in 1972, believed brought in from the Atlantic Ocean on the hulls and/or in ballast water of ships between 1940 and 1970, they said.
Grigg said the coral had spread to at least eight Oahu coral reef sites by 1979 and was found throughout the main Hawaiian Islands by the 1990s.
It wasn't known to harm the coral reef ecosystem until the scientists investigated Maui's black coral beds in 2001 with the Hawaii Undersea Research Laboratory submersible Pisces V.
COURTESY OF SAM KAHNG
A school of taape swim by an outgrowth of snowflake coral.
They found explosive snowflake coral growth at a 330-foot depth, carpeting up to 90 percent of the two black coral species commercially harvested, Grigg said.
"We don't really know the extent of how deep they go," Kahng noted. "It's quite scary."
The scientists will re-examine the black coral populations next month on the Pisces V. Meanwhile, they're studying Carijoa at the sunken ship YO2-57 off Waikiki and at other sites.
The alien coral is usually found about 200 feet offshore and begins spreading horizontally when it gets about half a foot tall, Grigg said.
"It grows so fast it's dominating hard surfaces in the ocean and it's displacing something else," Kahng said. "It will have an ecological impact. We don't know yet what it will be."
Carijoa riisei likes moderate current flow and shaded areas below or on the sides of a boat, buoy, wharf or pier pilings, the scientists said. It's a voracious feeder and grows fast, about 0.4 to 0.8 of an inch a week under favorable conditions, they described.
The coral has no known predators, and it's actually protected by sponges that hang on and keep them clean of other critters, Grigg said.
Invasive species severely damage or destroy local ecosystems, fauna and fisheries, but there are few such examples in marine tropical systems, the researchers said.
Of 287 introduced marine species in Hawaii, only four have become pests, and snowflake coral is the most devastating, Grigg said. The others are a mantis shrimp, barnacle and mussel.
In a papers written for the publications Pacific Science and Coral Reefs, Grigg points out that Hawaii's black coral fishery has been successfully managed for more than 40 years.
However, the resource is threatened now by Carijoa riisei, harvesting pressure and increased demand for black coral jewelry, he said.
Investigations of the fishery by submersible two years ago showed "the population is being squeezed from both sides," he said, explaining no big colonies are left and there are fewer new ones.
DEAN SENSUI / DSENSUI@STARBULLETIN.COM
Oceanographer Rick Grigg, left, and graduate student Sam Kahng are researching coral that may be threatening local reefs. In the bottles are two specimens. The one at left is relatively healthy and encrusted with two different types of sponges. The other is covered with a layer of algae.
More stringent management policies should be considered, Grigg said, suggesting an increase in the harvesting size limit from 36 inches to 48 inches. The state lowered the 48-inch size in 1998.
Grigg said he will meet with divers Aug. 4 to discuss a management change. "If they argue against it, we are looking at a possibility of running out (of black coral) in perhaps 10 years."
Carijoa coral is reported throughout the Pacific, but the species isn't known, the scientists said. "Is it nonindigenous like ours from the western Atlantic, or a different species?" asked Kahng, who would like to travel to other islands to explore those questions.
He said DNA can be used to figure out the genetic variability and age of the population and how it's spreading through the Pacific.
Rob Toonen, a marine population geneticist at the Hawaii Institute of Marine Biology at Coconut Island, is joining the project to do DNA analysis under the new research proposal, Grigg said.
