Starfish reef predator poses new threat

A crown of thorns starfish sits on a reef off Nihoa. A rise in numbers of the reef predator off some Northwestern Hawaiian Islands is alarming marine biologists. James D. Watt photo

By Jan TenBruggencate
Advertiser Science Writer

The crown of thorns starfish, which can devour coral reefs when its population booms, has increased ominously on several Northwestern Hawaiian Islands reefs.

The animals are natural parts of the reef, but like many species, they occasionally go through dramatic population changes. Colonies of the starfish eat living coral polyps and leave behind dead, white patches of bare coral. During severe infestations in Hawai'i, divers have been sent down with toxic syringes to inject and kill them.

The latest increase in population was detected at French Frigate Shoals, 400 miles northwest of Kaua'i, during a scientific expedition known as NOWRAMP 2002, the Northwestern Hawaiian Islands Reef Assessment and Monitoring Program. The expedition is surveying the nearshore waters of the western islands of the Hawaiian archipelago, with special attention to waters down to depths of 60 feet.

The starfish were noted during habitat surveys in which divers are towed across the reef by small boats, allowing them to assess large swaths of reefs fairly quickly. Numbers of crown of thorns starfish were larger this year on the windward side of French Frigate Shoals than they were in a similar survey two years ago.

During a previous expedition in 2000, "moderate abundances" of crown of thorns starfish were found at Pearl, Hermes and Kure Atolls, but not at French Frigate Shoals, said Rusty Brainard, chief scientist aboard the Townsend Cromwell, one of the two research ships on the 2002 expedition.

He did not express particular concern about the recent increase, which he said had also reached moderate abundance, but he issued a cautionary statement that "while a natural component of coral reef ecosystems, coral-eating crown-of-thorns sea stars can have devastating effects on coral reef communities when their populations increase to infestation levels."

The NOWRAMP 2002 survey also is studying algae populations across the reefs and atolls of the area.

"As we travel up the archipelago, team members are clearly seeing the differences between islands in terms of the balance between fish, coral and seaweed," said team leader Karla McDermid.

They have found some species that are rare in the main Hawaiian Islands, and some that have not been identified and may be new species. Included among those not yet identified are seaweeds with red coloration and bladelike leaves. Some are star-shaped and some have specialized foot-like attachments for holding on to the reef.

At Laysan Island, researchers found that dense seaweed beds support a large and diverse population of marine life.

"There are several crabs, lobsters, snails and other animals — many that feed on limu — that we've added to our species lists, and a sea anemone and crabs that have not previously been seen at Laysan," said Donald Potts, a seafloor life expert.

Researchers with the NOW-RAMP expedition are scheduled to return to port Oct. 7.

Reach Jan TenBruggencate at jant@honoluluadvertiser.com or (808) 245-3074.