Fighting a Crown of Thorns invasion on the reefs of the Philippines
Around us, corals are dying by the score - but the reef is silent. Beset by an invisible confetti of stinging plankton just off the coral-fringed waters of northern Batangas, I watch as a massacre unfolds.
Bristling with lethal toxin-tinged spikes, a multi-armed creature creeps menacingly towards a Porites coral head, its dull gray-green form blending well with the seascape. It is a Crown-of-Thorns Seastar (Acanthaster planci) - a dedicated coral predator and the bane of today's coral reefs. As it scales its quarry, it turns its brilliant ochre stomach inside out, ready to engulf and devour the coral's fleshy polyps. Suddenly, aluminium tongs slice the water to grasp the sea star in a mortal tug of- war. With a Lacrosse player's finesse, the tong-armed diver stuffs the creature into a nylon mesh and heads for a waiting boat above. Not quite divine intervention - but for the coral head, the next best thing.
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| Tong-armed diver keeps COTS at arm's length. Even light contact with its spikes can lead to instant swelling, numbness and nausea. A 2007 incident immobilized the author's arm for over an hour. (Kurt Domingo) |
The Porites coral and its kin are safe for now, but hidden in innumerable nooks and crannies around it are dozens more sea stars. Welcome to Etayo Cove - one of hundreds of reefs in the Coral Triangle under attack by these voracious fallen stars.
Perfect Coral Predators "This," says local warden, Agapito Perno, as he raises the same rapidly-deflating sea star, "Is locally known as Dap-ag. It comes every summer, when the sea is hottest." Known throughout the community as Mang Pete, Perno once served as a bosero or spotter for blast-fishers, but has since chosen to protect the coasts of his native Batangas. "Careful," he says when I peer in for a closer look.
"Very poisonous. Look only."
Widespread throughout the Coral Triangle, Crown-of-Thorns Sea stars (COTS) aren't actually star shaped. Rather, they resemble flattened sea-urchins, with 12 to 20 arms radiating from a central disc, densely coated by needle-tipped spikes. Mammoth appetites allow adults to chomp through six square meters of coral reef annually. An outbreak can be devastating - live coral cover in Palawan's Green Isle Bay plummeted from 70% to 10% in just a few months. Full recovery takes years and can be hindered by the inevitable growth of algae. When this happens, only browsers such as surgeonfish or rabbit fish can graze off enough space for new corals to develop.
"COTS are the perfect coral predators because of their highly-developed breeding and defence capabilities," explains WWF-Philippines CEO Jose Ma. Lorenzo Tan. "They are believed to have the highest fertilization rates of all known invertebrates. A tire-sized adult can spew up to 60 million eggs per batch, so if just 1% survives, 600,000 will - as Spock says - live long and prosper."
Few animals are better-engineered to deter predators: if the needle spikes don't stave off potential attackers, the neurotoxins they instantly inject into wounds often do. Still, large triggerfish, Triton Shells and colourful Harlequin Shrimp take a small but steady toll on COTS populations. Sadly, these hunters have been declining due to over-collection. With few natural control measures, COTS populations are determined only by the amount of corals they can seek.
Pollution, Climate Change Fuel Outbreaks
For millennia, COTS outbreaks have been instrumental in dictating the composition of the world's coral reefs. However, increased coastal pollution and ocean temperatures may be causing populations to skyrocket.
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| Stunningly-coloured Harlequin Shrimp (Hymenocera elegans) feed exclusively on the tube feet of sea stars - including the Crown-of-Thorns. A pair typically flips over and drags a sea star to a hidden lair, where the hapless echinoderm is eaten alive - sometimes for days. (Gregg Yan) |
Says Tan, "These sea stars play a crucial ecological role. Their constant browsing keeps fast-growing coral species in check, preventing them from dominating slow-growing, but equally important coral species. However, large-scale outbreaks - fuelled primarily by human activities - can wreak severe havoc and must be carefully managed to minimize long-term reef damage."
Human pollution is a real culprit: life amidst the world's oceans depends mainly on the natural upwelling of nutrients from decaying matter. Nutrients fuel the creation of vast clouds of free-floating algae and plankton, which are then fed upon by filter-feeders like corals. It is this crucial gauntlet that larval sea stars must brave before being able to settle on reefs.
However, pollution from coastal communities and offshore fleets has given rise to unusually high amounts of plankton - allowing more larval COTS to reach adulthood. Higher sea temperatures also cause coral-bleaching which - depending on the current health of a given reef - can either weaken or finish off its constituent corals.
"Ultimately, the best check-and-balance for COTS outbreaks would be to strengthen reef resilience itself. Healthy reefs have lots of filter-feeders. More filter-feeders mean less COTS. However," says WWF dive leader Paolo Pagaduan while inspecting a crateful of COTS, "Manual cleanups are still necessary."
Collecting Fallen Stars Back at Etayo Cove, the cleanup continues. Save for the rhythmic hissing of dive regulators, the reef is silent. Below, a tiny Watchman Goby pulls guard for its unlikely burrow-mate, a Pistol Shrimp.
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| COTS are dried before burial in Hamilo Coast. In just two hours, 247 sea stars were removed, bringing the summer season's total to over 1000. An earlier drive off Green Isle Bay in Palawan yielded over 30,000 - impressive, but not enough to save the reef. (Mark Limchoa) |
Beyond is a red baskets tar - no, a lionfish, feathered fins swaying in the current. With this, our dive leader starts his ascent, signalling the end of the trip. In the silence of the blue, all others follow suit. On the boat, COTS are emptied into plastic crates, the ones used for packing fruit. Soon the sea stars will be buried on land to avoid adding more nutrients to the sea, fuelling more outbreaks.
Concludes Tan, "Though eliminating hundreds of sea stars may sound inhumane, we recognize a need to reset nature's balance. We choose to control COTS populations because many of the Coral Triangle's reefs are no longer in good shape. Physical removal is the quickest and surest way to ensure the continued survival and productivity of these undersea oases."
As the sunset looms, we help the old caretaker bury the sea stars in a pre-dug pit along Hamilo Coast, a cool sea-breeze gradually drifting in. Mang Pete looks up, shoulders his shovel and motions for silence. The dozen-strong cleanup team perks up, the air still heavy with the stench of dead echinoderm.
"Today, we collect 247 Dap-ag. This is good, very good." Cheers and backslapping abound as the volunteers celebrate a fine day's work. When the crescendo finally dies down, the lone warden strolls back to his moored boat, towards the sea. I follow, if only to enjoy the dramatic sunset.
Abruptly he turns to me, his worried visage tinged crimson by the dying rays of the sun. "247 today, 1000 for whole season - but like the sea tide, they will be back." I catch his eye and slowly comprehend the truth behind his words. "These starfish ... they always come back."
A Porites coral head is brunch for a palm-sized sea star. With its toxin laden spikes, natural toughness and incredible reproductive capabilities, the Crown-of-Thorns Seastar is a perfect coral predator. (Kurt Domingo)
