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"Super Suckers" Slurp Invasive Algae Off Reefs

Scott Norris
for National Geographic News
July 30, 2007
 
In the battle against an exotic seaweed, biologists are employing a rather unusual solution: underwater vacuum cleaners.

The cleaners—called Super Suckers—suck up tons of gorilla ogo, invasive algae that are killing coral reefs, smothering sea grass beds, and fouling beaches in Hawaii.

Since 2006 the original Super Sucker, a barge-mounted device, has been operating in Kaneohe Bay, on the island of Oahu, where the seaweed invasion is particularly severe. (See a Hawaii map.)

At a recent scientific conference in Japan, biologists announced the arrival of "Super Sucker Junior," a smaller and more versatile unit that can operate in shallower waters and be easily transported between islands.

Alien Competitors

On land, non-native plant species sometimes outcompete native vegetation and take over habitat. The same phenomenon can happen in the sea. (Related: "It's Invaders vs. Invaders as Scientists Target Alien Species" [February 22, 2006].)

In Hawaii and elsewhere, scientists have noticed high-diversity coral communities shift to algae-dominated reefs with greatly reduced species diversity.

The problem posed by gorilla ogo and other invasive algae in Hawaii has been growing in magnitude for a number of years, experts say, and now has become dire.

"The algae invasion poses the largest current threat to the health of reefs in Hawaii," said Cynthia Hunter, a marine biologist at the University of Hawaii.

Thick coatings of algae can kill corals by blocking them from sunlight and flows of fresh seawater.

Some species have been particularly affected, Hunter said, including a species of rice coral that is now rapidly disappearing.

Algae also fill in the cracks and crevices that make coral reefs a safe haven for fish and other forms of marine life. Even larger animals such as sea turtles may be excluded from their normal resting areas.

"Removing the algae recreates the three-dimensional nature of the coral reef, and recreates homes used by all types of fish and invertebrates," said Brian Hauk, a director of the Super Sucker project with Hawaii's Department of Land and Natural Resources.

Gorilla ogo is just one of five exotic algae that now threaten Hawaii's reefs. Only one of the invaders arrived by accident—probably on the hull of a ship. (Related: "Invasive Bugs, Plants Prefer Summer Plane Flights, Study Finds" [April 11, 2007].)

The others were all brought to Hawaii deliberately for aquaculture research in the 1970s, Hunter of the University of Hawaii said. At that time, scientists were evaluating the suitability of different algae for commercial production.

Substances derived from marine algae are used for a variety of purposes in manufacturing and biological research, she said. When the research ended, the algae remained.

For two decades nobody really noticed: The algae were held in check by other marine life just as in their native environment.

But by the mid-1990s populations of algae-eating fish and sea urchins had declined, Hunter said, and the algae underwent an ecological shift.

"There was a tipping point about 10 to 15 years ago, and then the algae just took off," Hunter said.

"They invented a way of life that no one could have predicted: growing into dense mats 1- to 2-feet [0.3- to 0.6-meters] thick."

Sucking It Up

Each Super Sucker consists of a powerful pump and a tube for suctioning algae from beneath the ocean surface to the deck of a barge.

Divers in the water operate the 100-foot-long (30-meter-long) suction hose, feeding in gobs of algae by hand after first shaking loose any marine organisms that may be attached.

"They literally suck the algae off the reef," Hauk said.

Workers on the barge further screen the collected algae for any accidentally collected marine life. The nutrient-rich algae are then packed into bags for use as fertilizer. The Super Suckers can remove up to 800 pounds of algae per hour and restore hundreds of square feet of reef in a day, Hauk said.

"When you pull the algae off, there is often live coral underneath that is fighting to survive," Hauk said.

"You feel like you are saving the reef one [coral] colony at a time."

The Super Sucker project is a joint effort by The Nature Conservancy, the University of Hawaii, and the state's Department of Land and Natural Resources.

People Power

Using Super Suckers isn't the only way to clean up invasive algae. On the islands of Oahu and Maui, community volunteers have removed more than a hundred tons of algae from beaches and shallow waters.

But such efforts have not been able to keep pace with the invasion and are impractical in reef areas far from shore, experts say.

The Super Suckers provide a much faster and more efficient clean-up method, Hunter said, but they are only part of the long-term solution.

The ultimate goal is to turn the job of reef management back over the reefs' natural algal residents.

"Native algal consumers can keep [the invasive algae] from coming back," Hunter said. "The areas we are targeting will need to have those native communities restored."

Biologists are now starting to propagate native sea urchins—spiny, hard-shelled creatures with a strong appetite for algae. They hope to raise the urchins in captivity and then introduce them in reef areas where algae have been removed.

In addition, Hunter noted, new fishing restrictions should help allow populations of native reef fish to recover.

Studies have shown that in areas treated with the Super Sucker, native species can effectively prevent re-invasion, and new coral larvae begin to settle and grow.

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