Asia Dive News : Wave of predatory starfish decimate Palawan’s reefs

Locusts of the sea, they come by the thousands – and leave behind a watery graveyard of coral skeletons.

An enormous wave of coral-eating crown-of-thorns starfish (Acanthaster planci) is wreaking havoc on Palawan’s Green Island Bay, famed for harbouring one of the country’s few remaining populations of Dugong.

“The damage wrought by this year’s outbreak is very alarming,” said Sheila Albasin, WWF Roxas Population, Health & Environment Project Manager. “Live coral cover in one marine protected area dropped from last year’s 70% to a mere 10% - due mostly to starfish predation.”

Largest of its kind, the crown-of-thorns starfish or “cots” is a robust and voracious echinoderm that feeds exclusively on the tissue of living coral. A single adult can obliterate 10 square meters of healthy reef annually.

Unchecked, they pose a major threat to national food security - since a healthy square kilometre of coral reef can produce up to 30-tonnes of fish - or more importantly, food - yearly.

Cleanups Yield Thousands
Cots populations swell each summer, when the ocean is at its warmest. Outbreaks can reach plague proportions, with adults capable of laying up to 60 million eggs per batch.

To save remaining coral cover, a series of cleanup operations are being implemented by WWF-Philippines, the Local Government of Roxas and the Bantay Dagat, with help from the Western Philippines University, Community Environment&Natural Resources Office of DENR and a growing army of local volunteers and fishermen.

Over 30,000 of the poisonous starfish have been collected since late March, a painstaking process in which divers armed with hooks literally gaff individual starfish which are then disposed of on land. In comparison, cleanups in Apo Reef, the country's largest, yielded just 6,000 last year.

Cots cleanup efforts continue in the seven Marine Protected Areas (MPAs) of Roxas, covering the barangays of Tumarbong, Johnson Island, Malcampo, Rizal and Caramay.

Perfect Coral Predators
Growing to 40 cm, its sheer bulk, coupled with a dense coat of stinging spines up to 5 cm long, prove an effective deterrent against most cots predators. Predation of adults mainly falls to the Napoleon Wrasse (Mameng), Harlequin Shrimp, Giant Triton (Budyong) and larger types of pufferfish. Larval and juvenile cots are eaten by filter-feeders such as corals and tube worms. Sadly, much of the 25,000 square kilometers covered by Philippine reefs has been overfished: most of the predators that provide a natural control mechanism for the starfish are long gone.

WWF has been working for years to steward the rich marine resources of Green Island Bay in North Palawan, a critical component of the earth's Coral Triangle - an incredibly productive region that feeds a half-billion people yearly.
Whilst cleanups continue, locals are starting to report smaller outbreaks in adjacent Honda Bay, near the famed Dos Palmas Resort.

Source: WWF