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Sea urchins tested as algae removers

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    A diver from the Department of Land and Natural Resources Division of Aquatic Resources places native collector sea urchins on a patch of reef in Kaneohe Bay to study the effects of sea urchins grazing on algae abundance.
    Divers use a “Super Sucker” to remove alien algae from a patch of reef in Kaneohe Bay.

Native sea urchins — cows of the sea — and an underwater vacuuming system dubbed the "Super Sucker" might be the answer to saving Hawaii’s coral reefs from alien algae, which smother them.

Biologists from the state Department of Land and Natural Resources Division of Aquatic Resources are hailing the project as a success. It used the native collector urchins in conjunction with the Super Sucker in Kaneohe Bay for a year.

"It exceeded our expectations," state aquatic biologist Tony Montgomery said. "It actually worked better than we thought."

For the pilot project, begun in August 2009, divers manually removed the thick overgrowth of alien algae from a 3,000-meter test patch of coral reef in Kaneohe Bay near the Hawaii Institute of Marine Biology facility at Coconut Island.

The divers fed them up hoses of the Super Sucker. Meanwhile, others above the surface ensured that any creatures that may have inadvertently been gently sucked up with the algae were returned to their ocean home.

The biologists then placed 1,200 of the spiny creatures within 1,500 meters of the site; the other half of the test area was left urchin-free. The herbivorous urchins were allowed to graze freely on the invasive seaweed. Any urchins that roamed onto the wrong side were herded back to the urchin side of the test area.

The astounding results of the test showed that within five or six months the urchin side had little invasive seaweed left, while the algae on the other half grew back thicker than before.

"Very little came back on the side with the urchins," Montgomery said. "There was more algae this year than last year; 35 percent of the area was completely covered with algae."

During that two-week period in August, divers collected 15,000 pounds of the seaweed.

These non-native seaweeds were brought into Hawaii in the 1970s for experimental aquaculture projects, which were later abandoned, DLNR said. When they escaped and spread, some genera like Kappaphycus formed thick mats, choking out native seaweeds and smothering and killing corals and other organisms.

The experiment was funded by a $60,000 federal grant from the National Oceanic and Atmospheric Administration’s Coral Reef Conservation funds and the U.S. Fish and Wildlife Service with matching funds by the Hawaii Invasive Species Council.

Since their success with the sea urchin experiment, Aquatic Resources Division biologists are planning to use the methods in other areas as well as use free-roaming urchins on a larger scale. That requires a lot more urchins.

So the biologists are working on cultivating a large number of sea urchins at their retrofitted Anuenue Fisheries Research Center on Sand Island.

The next step for biologists will be to bring sea urchins to the test site with invasive algaes without clearing it first.

"We will see how they do with thousands of pounds of algae to eat," Montgomery said.


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