Sunday, June 20, 2010

(Sea) Star Wars: How Batangas Was Spared from an Outbreak of Coral-eating Starfish

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.

Brunch is Served by Kurt Domingo

As it scales its quarry, it turns its brilliant ochre stomach inside out, ready to engulf and devour the coral’s fleshy polyps. Suddenly, aluminum tongs slice the water to grasp the seastar 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.

The Porites coral and its kin are safe for now, but hidden in innumerable nooks and crannies around it are dozens more seastars. 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 seastar, “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.”

COTS Burial by Mark Limchoa

Widespread throughout the Coral Triangle, Crown-of-Thorns Seastars or 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 rabbitfish can graze off enough space for new corals to develop.

“COTS are the perfect coral predators because of their highly-developed breeding and defense 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 colorful 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.

Says Tan, “These seastars 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.”

COTS on Acropora by Wesley Caballa

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 seastars 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. Beyond is a red basketstar – no, a lionfish, feathered fins swaying in the current. With this, our dive leader starts his ascent, signaling 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 seastars will be buried on land to avoid adding more nutrients to the sea, fuelling more outbreaks.

Concludes Tan, “Though eliminating hundreds of seastars 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 seastars 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 one day be back.” I catch his eye and slowly comprehend the truth behind his words. “These starfish … they always come back.”
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