Thorny starfish continues to threaten PH coral reefs

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Saturday, November 24, 2012

THE crown-of-thorns starfish (Acanthaster planci) is a cross that coral reefs must bear.

Crown-of-thorns starfish feed on the polyps or living tissue of corals. Unlike most starfish, one would not think of using them as house décor. The crown-of-thorns starfish can grow up to 80 centimeters and has 21 arms, which are covered in long, sharp spines. These spines, which resemble a crown, earned the organism its name.

According to the Coral Reef Research Centre (CRRC), healthy coral reefs with 40 to 50 percent coral cover can support 20 to 30 crown-of-thorns starfish per hectare.


“Some reefs seem to support small populations of crown-of-thorns starfish for many years, with only a small reduction in coral cover,” said the CRRC in its website.


“(But) during crown-of-thorns outbreaks, one of many threats to coral reefs today, coral cover, species diversity, and coral composition are affected, and within a few weeks coral skeletons may be overgrown by algae, possibly causing an ecological shift in coral reef ecosystems,” wrote marine ecology professor Arthur Bos of the American University of Cairo in Egypt in a study on the management of crown-of-thorns outbreak, published in the journal Ocean and Management 2012 edition.

An outbreak occurs when more than 1,500 crown-of-thorns starfish are found in one square kilometer.

Hermes de Dios, a marine biologist at the Southern Leyte State University, reported an crown-of-thorns outbreak in Southern Leyte early this year.

The report prompted local governments in the area to allot funding for the extraction of crown-of-thorns starfish, but even then de Dios told the 44th Annual Convention of the Federation of Institutions for Marine and Freshwater Sciences last month that 90 percent of the coral cover off Sogod Bay in Southern Leyte have been lost.


“This is worse than bleaching, recovery could be from 50 to 100 years, depending on conditions,” he said during a presentation at the convention sponsored by the Cebu Technical University.

The Philippine Coral Bleaching Watch ( received a still unverified report of a crown-of-thorns starfish outbreak in the Monad Shoal, off Malapascua Island, Cebu last January.

The CRRC said that while the population of crown-of-thorns fluctuate, some factors may cause their numbers to multiply.

One factor is the removal of its natural predators and the other is human activities in coastal areas, which caused an increase in nutrients flowing to the sea, resulting in more planktonic food for the larvae of the crown-of-thorns starfish.

De Dios said he is studying another method of killing the crown-of-thorns using homemade solutions, but he declined to give details pending further research.

He stressed the need to study the outbreak, its effect on food supply and tourism activities and ways to prevent crown-of-thorns starfish population from increasing.

Published in the Sun.Star Cebu newspaper on November 25, 2012.

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