Coral reefs around Pag-asa Island are facing a combination of physical destruction, overharvesting and worsening climate stress, with scientists from the University of the Philippines Marine Science Institute (UP MSI) reporting severely degraded reef conditions in some shallow areas.
At a mini-symposium on the West Philippine Sea on September 29, UP MSI researchers described reef flats where hard coral cover has fallen to only about 1% to 2%, while some commercially valuable marine species have been depleted.
Dr. Fernando “Ando” Siringan, professor and head of the Geological Oceanography Laboratory at UP MSI, said the condition of Pag-asa’s reefs reflects both local damage and broader environmental pressures.
“Ang hindi maganda, ang coral cover ng Pag-asa ngayon ay halos 1 to 2% na lamang. At yan ay totoo sa maraming coral reef… Kailangan may aktibong gagawin tayo para mapanatili natin yung kalusugan ng coral reef. Ang pangangalaga natin sa coral reef ay pangangalaga din natin sa sarili natin,” Siringan said.
Researchers also documented physical damage to reef flats linked to past giant clam harvesting.
Siringan said foreign harvesting boats had used their propellers to scrape shallow reef flats in search of giant clams, locally known as taklobo.
“Sa iba’t ibang isla kung titingnan natin… sa reef flat may kayod, kasi hinarvest ng mga Intsik ang taklobo… yang mga yan ay hindi coral, yang mga yan ay kudkod ng mga boat… gamit yung kanilang propeller… Sa Rizal na na-calculate na mga 1.75 sq km within the atoll ang kinudkod at napakalawak nyan,” he said.
The damage, he said, included about 1.75 square kilometers of reef within Rizal Reef based on calculations presented by the researchers.
Dr. Maria Celia “Machel” Malay, professor and head of the Marine Biodiversity and Evolution Laboratory at UP MSI, said the depletion of giant clams and sea cucumbers was also evident in surveys of Pag-asa’s shallow reef flats.
“May mga giant clams, mga taklobo at manglot. Ah yung isa, yung pinakamalaki, ay fossils na lang. Ito yung kino-collect nung mga Chinese… May hinahanap kaming isang napakalaking shell sa reef flat pero wala namang buhay… matagal nang naubos sa Pag-asa,” Malay said.
She also observed signs of overharvesting among sea cucumbers, with mostly lower-value species remaining.
“May hinahanap kaming isang napakalaking shell sa reef flat pero wala namang buhay… matagal ng naubos sa Pag-asa… Ang napansin ko ay yung mga sea cucumbers puro mga low value… may signs talaga of overharvesting,” she said.
The researchers said the ecological pressure is not limited to the loss of individual species.
Dr. Laura David, professor and head of the Ocean Color and Coastal Oceanography Laboratory at UP MSI, said fish biodiversity remains high in the area, but the number and biomass of fish have declined.
“We still have high biodiversity ng fish. Pero pag binilang mo ilan yun? Konti na lang sila. Pwede kang mag-swimming, wala kang makikitang isda… Mababa na talaga yung density including overfishing including destruction of the habitat,” David said.
Warming adds pressure
The physical damage and overharvesting are occurring alongside changes in the marine environment associated with a warming climate.
David said UP MSI researchers analyzed 30 years of satellite data, covering 1993 to 2023, to examine climate conditions across the West Philippine Sea.
“Kasi ang climate talaga dapat 30 years data… So from 1993 to 2023 na datos mula sa satellite images or satellite data, tiningnan namin kung ano-ano nga ba nararamdaman ng Pilipinas. Tapos clinaster namin siya sa mga magkakamukha ang nararamdaman… The West Philippine Sea is divided into three: Northern, Central, and South part,” David said.
The study found sea-level increases of about 30 to 41 millimeters per decade across the West Philippine Sea, while sea surface temperatures off Palawan were increasing by about 0.16 to 0.18 degrees Celsius per decade, according to the researchers.
David said the Central West Philippine Sea cluster also recorded six extreme rainfall events involving 100 to 200 millimeters of rain over short periods.
“Overall ang Pilipinas, mas mataas umakyat ang dagat niya kaysa the rest of the world… Sa Central, mas grabe siya kasi nagkaroon siya ng anim na beses na ganun yung ulan [100 to 200 mm in a short spot]… So may pagkakaiba talaga sila and this forms like a threat or a background of what is happening in the area,” she said.
Siringan said warming seas can further weaken coral reefs through repeated bleaching.
“Ang isang consequence ng pag-init ng tubig dagat ay dumadami ang nabi-bleach… At kung meron kang corals na na-bleach, yung kanilang kakayanan para labanan ang lakas ng alon bumabagsak din… The bleaching would weaken the reef itself and probably yung nakita natin na nagiging basag-basag ang coral ay dahil na rin sa dumadami ang bleaching events,” he said.
He said the climate pressures are expected to continue affecting low-lying islands and reefs.
“Sea level is rising. That’s a driver of coastal erosion… Sea level rise will continue, the marine heatwaves will continue, and projections also indicate that yung bagyo pwedeng hindi dumami pero pwedeng maging mas malakas,” Siringan said.
David also cited the impact of typhoons on the Kalayaan Island Group, including Pag-asa and Parola islands.
“Nung dumaan si Typhoon Rai, si Pag-asa at si Parola naman ang tinamaan… So pwedeng monsoon, pwedeng bagyo,” she said.
From damaged reefs to a changing sea
The researchers’ findings point to overlapping pressures on the West Philippine Sea: reef structures damaged by destructive harvesting, depleted marine resources and environmental changes associated with warming seas and rising sea levels.
For Siringan, protecting coral reefs is therefore not only about conserving biodiversity but also about maintaining the natural systems that support coastal communities and marine resources.
“Ang pangangalaga natin sa coral reef ay pangangalaga din natin sa sarili natin,” he said.
The findings were presented during “Our Natural Heritage: Geology, Ecology, and Biodiversity of the West Philippine Sea,” a UP MSI mini-symposium held on September 29 as part of the 2026 Maritime and Archipelagic Nation Awareness Month (MANA Mo).
The event also highlighted the role of sustained scientific research in documenting changes in the West Philippine Sea, including the condition of reefs, marine biodiversity and the physical environment.
