MANILA, PhilippinesThe Philippines is one of the top five countries with the most coral reefs in the world. It lies within the Coral Triangle, a marine area in the western Pacific Ocean with the highest marine biodiversity, and has the third most extensive reef system, spanning across 25,060 square kilometers.

The Philippines is home to 600 hard coral species. However, decades of pollution, destructive fishing, and overfishing have taken a toll. 

But climate change poses the greatest threat: record-breaking global temperatures, worsened by rising greenhouse gases, fuel ocean warming and acidification.

In March 2024, the National Oceanic and Atmospheric Administration’s (NOAA) Coral Reef Watch reported that the world will soon be experiencing the fourth and worst mass coral bleaching event in history.

Australia’s Great Barrier Reef is already suffering, and the Philippines’ Tubbataha Reef and Apo Island Marine Reserve are projected to be impacted as the bleaching engulfs the Southern Hemisphere.

Warming oceans and ghost-white corals

The ocean is the largest carbon sink, absorbing about 31% of the carbon emissions released into the atmosphere. However, the increasing amount of greenhouse gases in the atmosphere has led to the warming and acidification of the ocean, causing coral bleaching. 

Coral bleaching is a phenomenon in which corals lose their color and turn white due to stress. When subjected to heat, corals expel the colorful algae living in their tissues, which makes them more susceptible to diseases as these algae are their primary source of food.

On the other hand, ocean acidification has slowed the rate at which corals generate calcium carbonate, which helps the growth of coral skeletons. Severe acidity also causes the corals’ skeletons to dissolve quickly.

While bleaching events can greatly damage coral reefs, they are not a death sentence. Corals can survive bleaching events and recover over time, as long as stressors do not persist.

Moreover, several studies show that there are parts of the ocean where coral reefs seem to decline slower and recover quicker. These areas are called climate refugia.

Climate refugia are areas buffered from climate change which enable species, communities, and ecosystems to persist long-term. In the Philippines, some areas are believed to be climate refugia.

According to Dr. Rene Abesamis, an associate professor and coral reef ecologist from the University of the Philippines (UP) Marine Science Institute (MSI), some studies have observed the Bohol Sea and a part of the Sulu Sea to have potential climate refugia for coral reefs.

However, Abesmis stressed the concepts of climate refugia and climate resilience in corals remain poorly defined despite numerous studies.

“The idea is not that we have them [climate refugia]. Nobody really knows we have them because the time scales involved are quite long—we’re talking decades. When a bleaching event hits a coral reef, it takes a while before that recovers. That’s why it’s at the edge of scientific investigation,” he said.

Beyond the long study timescales for coral reef resilience, Abesamis emphasized the influence of various factors. Coral traits, proximity to disturbances like pollution, and nearby human activities all affect resilience.

“There are so many species of corals, and some of them are slow growers, some of them are fast growers, and some of them are more sensitive to bleaching than others,” he added.

This bears the question asked by marine scientists all over the world—according to Abesamis—“Where are these climate refugia where corals can avoid decline and persist longer?”

A possible climate refugium: the Bohol Sea

The NOAA Coral Reef Watch bleaching alert projection shows that the Bohol Sea in the Philippines exhibits little to no stress, supporting the study that identifies it as a climate refugium for coral reefs. (Screenshot from the NOAA Coral Reef Watch Coral Bleaching Heat Stress Monitoring page)

The Bohol Sea, also known as the Mindanao Sea, stretches to about 270 kilometers, near the islands of Camiguin, Siquijor, Leyte, Bohol, Negros, and Mindanao, among others. Bohol Sea has 184 Marine Protected Areas (MPAs) and 145 documented coral species.

Abesamis said that Bohol Sea, Palawan, the Visayan Sea, and Tawi-Tawi were identified as potential climate refugia for coral reefs in the Philippines. 

Given the large network of MPAs in Bohol Sea, he is investigating whether they overlap with climate refugia or provide protection for climate-resilient reefs.

“The geographic region that the study identified is basically the passageway between the Pacific Ocean and the Sulu Sea where a strong current and relatively cooler waters coming from the Pacific passes through. That’s also the mechanism for connecting populations of the coral reefs,” Abesamis said.

Besides water currents and temperature, other factors also determine the resilience of coral reefs. Abesamis said the term “resilience” has a broad definition, and simplified it as the factors that allow coral reefs to avoid stressors.

Some of these factors include the coral’s tolerance to heat stress, its ability to bounce back from a disturbance, its condition prior to the disturbance, the speed of heat build-up in its surrounding waters, and its connectivity with other reef systems.

“What’s more important to say is that there are efforts globally to try to understand this at least on the global scale, to see where these areas are with the potential for coral reefs to persist and perhaps even recover more quickly or at least, slow down their decline,” he said.

Citizen science in action

Local stakeholders in Negros try using MPA-FishMApp, a fish monitoring and data collection application to be used in Dr. Rene Abesamis’ Pew project. (Marynoll Susmeña.)

Abesamis seeks to identify climate-resilient coral reefs in the Bohol Sea and lay the groundwork for their protection with the help of citizen scientists.

He will be pursuing a three-year project as a 2024 Pew Marine Conservation Fellow of The Pew Charitable Trusts, which awarded him $150,000 for the conduct of the project.

“The declines in coral reefs seem almost inevitable right now with the projections but by identifying those places which some people in certain publications refer to as climate refugia for coral reefs, maybe in those places we can beef up some management or conservation efforts to try to keep these reefs growing and their ecosystem services,” he said.

Abesamis also shared that he finds this project “exciting and interesting” because “you can direct some of the limited resources to try and help a cause if you knew where to put your efforts.”

Recognizing the lack of marine scientists to cover the vast Bohol Sea, Abesamis plans to involve local communities through citizen science.

Abesamis will be collaborating with local researchers and training local fisherfolk to help survey coral reefs in two marine protected areas. He will also work with leading marine scientists who have data from the region to develop indicators, such as coral diversity and reef fish abundance, to pinpoint climate-resistant reefs. 

To share species-level data, Abesamis will use a platform called Mermaid for trained scientists. For citizen scientists, two new tools will be utilized: Alwan for monitoring corals and MPA-FishMApp (FishMApp) for monitoring fish.

FishMApp focuses on observing healthy ecosystems that support fisheries. It leverages the knowledge of fishers by allowing them to use local fish names within the app. Abesamis said the platform simplifies data entry, and with repeated observations, it generates graphs showing the health of the MPA based on fish abundance.

Meanwhile, Alwan uses photos to analyze coral communities and estimate coral cover to help identify potential resilience indicators in coral reefs. The platform still needs an expert to analyze the data, but they hope for that to change in the next two or three years with the help of artificial intelligence.

He expects these databases to effectively consolidate data, streamlining information sharing with environmental managers. 

“More data can tell us where those climate-resilient reefs are. At the local level, that can inform decisions by stakeholders to prioritize the protection of certain places that show up to be resilient based on certain frameworks. But all of that has to be elevated to the national government to put that into strategies and policies,” he said.

Abesamis suggested integrating the project’s findings into Department of Environment and Natural Resources technical bulletins. This would inform local communities on best practices and opportunities for citizen science data collection.

‘An ambition to create an impact’

Dr. Abesamis’ Pew project highlights the involvement of citizen scientists in the monitoring and collection of data on coral reefs in the Bohol Sea. (Marynoll Susmeña)

In the next three years, Abesamis hopes the project will yield results that would give clarity on the scientific understanding of the ecology of places that tend to be more resilient than others.

“I think we need to put some ideas together to try to gain more momentum and maybe prioritize certain places or at least build up information so that we know better. It sounds ambitious, right? But it’s meant to pilot an idea and then try to make a bigger impact,” he said.

Another aim of the project is to work toward some of the targets of the Kunming-Montreal Global Biodiversity Framework: to protect 30% of the critical habitats for biodiversity by 2030, and to ensure inclusive participation of local communities in decision-making related to biodiversity.

While aware of climate change and coral bleaching, local stakeholders have questions and ideas to share. Abesamis is eager to learn their perspectives and collaborate on solutions.

With NOAA Coral Reef Watch’s report on the worst coral bleaching event in history, Abesamis recognizes that there is not much that can be done and that nobody knows how likely the climate-resilient corals will survive it.

“For now, we can only test things, hypothesize, and observe. We’re at the early stages of understanding climate-resilient reefs because it’s unfolding before us. We have frameworks, but in the end, we will only know if a place is resilient if it actually persists over a long time,” he said.