In picturesque Boracay, a crown-of-thorns infestation is eating away at the reef

BORACAY ISLAND, Philippines — Authorities and residents have reported the return of seashells on Boracay’s beaches and sightings of scop owls — signs that they say show the island is slowly but surely recovering from years of environmental degredation.

Its underwater ecosystem tells a different story: local officials say they fear the island’s coral reefs are being badly affected by an invasion of crown-of-thorns starfish.

Among the largest starfish in the world, crown-of-thorns (or COTS) are a bane for the hard, stony corals that they feed on, says Haron Deo Vargas, a local marine biologist.

Coastal and agricultural runoff are the primary drivers for a surging COTS population. Overfishing of its fish predators can also trigger an outbreak, as can an increase in the water temperature. But whichever the case, a COTS infestation points to an unhealthy reef ecosystem.

Vargas, who also works in the government-run Community Environment and Natural Resources Office (CENRO), tells Mongabay that he’s received reports from fisherfolks of these undersea infestations for several months. Until the start of July, however, he was unable to confirm them due to the COVID-19 imposed lockdown.

On July 6, the Department of Tourism allowed the CENTRO office to conduct dives to check up on a possible COTS outbreak after the island was allowed to reopen to local tourists, the main driver of the local economy.

Vargas’s group confirmed that the reports were correct: the crown-of-thorns starfish are proliferating among Boracay’s reefs.

This isn’t the first time Boracay’s reefs have suffered from a crown-of-thorns infestation. Vargas says an outbreak occurred in 2018, which covered Boracay’s corals and its outlying areas. In July last year, the waters of Culasi on the nearby island of Panay also saw a crown-of-thorn outbreak that spread into the neighboring tourist islands of Mararison and Maniguin.

This year, similar outbreaks are being reported in nearby Tangalan, a boat ride away from Boracay, says environment officer Glenda Sanchez.

Like Boracay, the coastal town has white sand beaches and is having difficulty monitoring its marine resources due to the lack of volunteer divers.

“Even if we were allowed to go diving, our resources are limited at this time and we lack manpower from the pool of divers,” Vargas says. “Many of our volunteer professional divers have returned to their provinces and cities soon after the COVID-19 pandemic. They won’t return here to help.”

To tackle the outbreaks, divers pick crown-of-thorns off the reef, says Mylen Arboleda of Dive Gurus, a member of the Boracay Association of Sport and Scuba Diving (BASS), which helps monitor the condition of Boracay’s reefs.

“Back in 2018, we collected more than 15,000 kilos [33,000 pounds] of the crown-of-thorns after a one-month relentless campaign and operation,” she says. This time, however, the pandemic means that most of the volunteer divers are not on the island.

Underwater visibility caused by warming sea temperatures poses another problem, Vargas says. Visibility is low in the prime summer months, which begin in April and last until June or July. The hot summer months also see a rise in plankton and algae blooms.

Vargas says the only solution he can see is to train another set of divers and also engage fisherfolks in keeping the crown-of-thorns at bay.

“What we are planning to do is to train available divers and some fishermen on how to inject vinegar to the crown-of-thorns to kill them,” Vargas says. “Another option is we manually collect the crown-of-thorns and properly dispose it.”

This story was originally published on Mongabay on 23 July 2020 as part of an EJN-supported project called Mongabay Environews Philippines. It has been edited for clarity.

Banner image: Crown-of-thorns sea stars have led to the decline of many coral reefs / Credit: Rhett A. Butler/Mongabay