“Crown of thorns” threaten Subic Bay reefs
By Henry Empeno

SUBIC BAY FREEPORT — Thousands of poisonous crown-of-thorns starfish have infested at least two coral reefs in Subic Bay, threatening important shelters for marine life, as well as diving spots that have made Subic a popular tourism destination.

The crown-of-thorns starfish, scientifically known as Acanthaster planci, is a predator of hard corals that could reduce reef corals to a mass of skeletons in a matter of weeks, marine zoologists here said.

The venomous starfish specie, known locally as “taeng kalabaw”, is said to feed on its coral prey by extending its stomach out of its mouth in a thin sheet, then digesting the living coral tissue from the coral skeleton.

After several hours, the starfish moves away, leaving the coral starkly white and lifeless.

According to the Subic Bay Metropolitan Authority (SBMA), about 700 meters of the three-kilometer fringing reef southwest of Grande Island here have shown extensive bleaching and fouling as a result of infestation.

The same has been noted at the one-kilometer fringing reef near Hidden Beach, east of Grande Island.

The thorny starfish were found in scattered colonies in waters from one meter to 40 meters deep, said Dorothy Joyce Ardiente, a marine zoologist at SBMA’s Ecology Center.

The infestation, Ardiente said, was first reported after consultants for the SBMA’s coastal resource management program made a monitoring survey at the Grande Island reef on February 1 to 2.

A report by survey team leader Ruben Estudillo said that during one 20-minute dive, the team counted about 80 crown-of-thorns starfish, including young individuals, that voraciously feed on coral polyps.

The crown-of-thorns colonies were seen attacking various forms of corals, including branching and tabular species, massive and encrusting corals, as well as solitary forms such as mushroom corals.

“Obviously, such number obtained would represent an outbreak,” Estudillo warned in his report.

“If no immediate control measure is done, the large number of Acanthaster observed could swiftly reduce the small reef to a mass of dead corals skeletons, which will be rapidly overgrown with algae,” he added.

Because of the reported outbreak, the SBMA has called on the help of volunteers from dive shops in the Subic Bay area, said Ecology Center head Amethya Dela Llana-Koval.

“We expect the clean-up operations to last for a few months, so we’re calling on more volunteers to help save Subic’s coral reefs,” Koval said.

The volunteer divers, accompanied by personnel from the Ecology Center and the SBMA Harbor Patrol, have been conducting collection operations almost daily since last week, and coming up with about a hundred crown-of-thorns starfish for each half-day dive, Koval said.

Last week, divers from the Ocean Adventure collected a total of 435 crown-of-thorns, she said. On Tuesday, volunteers from Diver Down International came up with 100, Boardwalk Dive Center with 300, and Master Dive with 90, Koval added.

Ecology Center’s Ardiente said the divers use sticks and tongs to pry the crown-of-thorns starfish off their coral prey, then bag them for disposal onshore.

“It’s a painstaking job,” Ardiente said. “The starfish have long barbs that could inject poisonous stings. The divers have to be very careful in handling them.”

Estudillo also said in his report that this is the first time that a crown-of-thorns outbreak has been observed here in Subic Bay.

Similar outbreaks, however, have been reported at Apo reef and Puerto Galera in Mindoro, Mabini in Batangas, Roxas in Palawan, Bolinao in Pangasinan, and Kiamba and Glan in Sarangani Bay, an article on the World Wildlife Fund’s website said.

Estudillo added that there are experts who say that the outbreaks are a naturally recurring phenomenon, while others believe they are a result of over fishing, especially of the crown-of-thorns’ natural predators.

Among these predators, he added, are reef fishes such as the hump-headed wrasse and puffer fish, and the giant triton, a mollusk often collected — illegally — for its decorative shell.

Quoting researches into similar outbreaks in the 1960s and 1970s, Estudillo added that infested reefs could recover from 10 to 40 years, and that is if further infestation does not occur. (30)