Mangroves and seagrasses: Mitigating climate change through blue carbon

Coastal areas are natural carbon sinks. (Henrylito Tacio)

By Henrylito D. Tacio

Carbon dioxide is one of the Earth’s most important greenhouse gases: a gas that absorbs and radiates heat. “Without carbon dioxide, Earth’s natural greenhouse effect would be too weak to keep the average global surface temperature above freezing,” wrote Rebecca Lindsey for the US National Oceanic and Atmospheric Administration website, 

But too much carbon dioxide in the atmosphere is bad for Earth. “By adding more carbon dioxide in the atmosphere, people are supercharging the natural greenhouse effect, causing global temperature to rise,” Lindsey explained. 

Carbon cycle experts estimate that natural “sinks” – processes that remove carbon from the atmosphere – on land and in the ocean absorbed the equivalent of about half of the world’s annual carbon dioxide the world emitted each year in the 2011-2020 decade, studies showed.  

“Because we put more carbon dioxide into the atmosphere than the natural sinks can remove, the total amount of carbon dioxide in the atmosphere increases every year,” pointed out Lindsey.  

Blue carbon  

In time, blue carbon came into existence. The Nobel-prize winning Intergovernmental Panel on Climate Change (IPCC) defines blue carbon as “All biologically-driven carbon fluxes and storage in marine systems that are amenable to management.”

 In other words, “Blue carbon is the carbon captured/sequestered, stored and stabilized by plants that grow near the coasts,” explained Russell Christine B. Corcino, a Research Assistant of the Institute of Biology, College of Science at the University of the Philippines-Diliman.  

Imagine this: human beings exhale carbon dioxide and this exhaled carbon is being “inhaled” by plants. “Once inhaled, they use the carbon to make food and plant parts (leaves, stems, etc.), thus storing the carbon in their plant parts,” Corcino said. “They can also store it in the soil once they die or when plant parts fall off and get buried in the soil. The soil stores higher carbon than the plant parts.” 

Carbon sequestration

 Seagrass meadows and mangrove forests have natural capacity to sequester and store enormous amounts of carbon in their ecosystems.

 “As carbon sinks, they are a cheap and readily available natural resource useful in mitigating the negative impacts of climate change,” said the late Dr. Miguel D. Fortes, a marine scientist and author of several books and technical articles in refereed journals.

Coastal areas are natural carbon sinks. (Henrylito Tacio)

 Mangroves and seagrasses can store or capture more than twice – or even four to five times than those forests growing in the uplands. They largely contribute to “our goal of decreasing carbon dioxide in the atmosphere.” In simpler terms, they can be used to adapt or mitigate against the impacts of climate change.   

“Mangroves and seagrasses are also natural nurseries for juvenile fishes and other commercially-important marine species (examples: milkfish, crabs, shrimps),” said Corcino. “Their ability to decrease wave impacts are also recognized. Studies showed that in Visayas, coastal villages with sufficient mangrove areas suffered lesser casualties and damages from typhoon Yolanda than those with low mangrove cover.” 

These ecosystem services are touted as “nature-based solutions” since they can perform these sustainable services free of charge for human beings. In fact, blue carbon ecosystems have become integral for climate change adaptation and mitigation programs. 

Extremely effective 

Recent studies conducted by the United Nations Environment Program (UNEP) and International Union for Conservation of Nature (IUCN) found that, when mangrove forests, saltwater marshes and seagrass meadows are preserved, they are “extremely effective” at storing carbon. 

In 2009, the concept of blue carbon was introduced to draw attention to the degradation of marine and coastal ecosystems and the need to conserve and restore them to mitigate the impacts of climate change and to recover for the other ecosystem services they provide. 

Just recently, five Filipino scientists have come up with a study, entitled, “Status, limitations, and challenges of blue carbon studies in the Philippines: A bibliographic analysis.” 

 Corcino is the lead author of the study. The other four were Maria Elisa B. Gerona-Daga, Shaina C. Samoza, John Kenneth R. Fraga, and Severino G. Salmo III. The study was funded by the Department of Science and Technology (DOST) through the Philippine Council for Industry, Energy and Emerging Technology Research and Development (PCIEERD) and partly-funded by the United States Agency for International Development (USAID) through the Partnerships for Enhanced Engagement in Research (PEER) program. 

Philippine experience 

“Mangrove and seagrass ecosystems (in the Philippines) have been studied since the 1970s but only recently on its carbon storage capacity,” they wrote. 

“From our study, we computed that the amount of carbon stored in the country’s existing mangroves and seagrasses alone is around 80,000 times more than our carbon reduction commitments to the United Nations,” Corcino explained in an exclusive interview. 

They found out that the carbon storage rate of Philippine mangroves is at 400 Megagram per hectare (Mg/ha), while that of seagrasses is at 80 Mg/ha. “This rate is around half of the average global carbon storage rate,” she said, but added that the estimates were based on very few data points. 

In their study, the estimates came from three collected data for seagrass and less than 30 for mangroves. “(This is) not quite representative for an archipelagic country like the Philippines,” Corcino said. “If we can increase our data on blue carbon storage, then probably the carbon stock values can increase and might even exceed that of other Southeast Asian countries.” 

Mangroves versus seagrasses

 On why more estimates were from mangroves and less for seagrasses, she explained, “This is actually surprising and sad at the same time since around the 1990s, seagrass studies exceeded those in mangroves. It was only around the late 2000s, from 2009 onwards, when mangrove studies increased gradually.”  

Since there were no studies at hand, the researchers could only surmise the factors contributing to this difference. “These include the lack of experts, the difficulties in the logistics of studying seagrass as compared to mangroves, and the difference in appreciation and prioritization.” 

According to Corcino, mangroves are explicitly mentioned in the list of protected areas declared by the Department of Environment and Natural Resources (DENR) or even in policies. There is even a national law in the Philippines explicitly restricting the cutting or harvesting of mangroves.  

“This gives mangrove-related projects higher chances of approval since they are a priority by law,” Corcino argued. “On the other hand, seagrasses do not have this edge. Protection for seagrasses are usually just ‘by-products’ or ‘side-targets’ of protecting other ecosystems like coral reefs or mangrove forests.”  

Another possible reason why seagrasses were left in most recent studies is the difficulty in studying them. “Conducting surveys in seagrasses is also challenging given its underwater nature,” she said. “There is the need to learn to dive and retrieve waterproof or underwater equipment. These are usually more expensive than just walking in the forest. Even remote sensing techniques for seagrasses are still being developed to account for their underwater nature. 

Most of all, perceptions and awareness also mattered. Most Filipinos look at mangroves as forests, which are easily connected to other forest types, as areas that give shade and protection. Since they are decreasing like most of our forests, they must be protected.  

But such is not the case of seagrasses. “They are seen as ‘grasses’ and what is the usual mindset when people encounter grasses?” Corcino said. “They are seen as weeds that must be cut or trimmed. I believe, if we can change these views, we could improve appreciation and thus initiatives for seagrasses.” 

Vanishing mangroves and seagrasses 

Nevertheless, both mangroves and seagrasses are suffering the same fate. “They are at great risk of being lost and if the trend continues at current rates, a further 30-40% of seagrasses and nearly all unprotected mangroves could be lost in the next 100 years,” deplored Dr. Fortes, the first Filipino to receive the prestigious International Biwako Prize for Ecology. 

Now, if these mangroves and seagrasses disappear, “their carbon sink capacity is lost or adversely affected, and the carbon stored is released, resulting in emissions of carbon dioxide that contribute to climate change,” the IUCN warned.

Mangroves can sequester carbon dioxide from the atmosphere more than twice than tropical rainforests. (Henrylito Tacio)

 That warning must be heeded. “Mangroves and seagrasses still continue to experience damages or clearing from natural disturbances and human activities,” Corcino said.

 On the brighter side, however, there are local sites that are effectively managed, according to Corcino. “There are also more programs and projects nowadays that push for mangrove and seagrass conservation and restoration,” she said. “We still hope that, someday, conservation and development would find a middle ground and achieve true sustainability.”

 Now, going back to blue carbon. Corcino stressed that their study emphasized the huge potential of mangroves and seagrasses “Our study emphasizes the huge potential of mangroves and seagrasses in reducing the carbon released to our atmosphere,” she stressed.  

“Because of this, they are also large carbon reservoirs. The carbon remains stored as long as these ecosystems are intact. But if they are destroyed, their carbon gets released to the atmosphere as carbon dioxide. This further strengthens the need to conserve them.”  


In their study, the researchers provided several recommendations on how to better conserve blue carbon in the country. “In addition, our study identified the gaps that must be addressed for more optimized research, conservation, and restoration of blue carbon ecosystems. 

Corcino enumerated some of these: “These include the urgent need to assess and monitor our blue carbon ecosystems especially seagrass meadows; translation of existing information into policy and ‘laymanized’ knowledge; and utilizing networks to further expand assessment and conservation works to other sites.”

 In their study, the researchers also provided some recommendations. “Our project has proposed and advocated three major steps for this: Connect, Protect, and Mitigate. Connecting would be the most important, since without the cooperation of stakeholders and involved agencies, it would be impossible to sustain the ‘Protect’ (that is, blue carbon research and conservation) and ‘Mitigate’ (that is, climate change mitigation) part.”  

Blue carbon is recognized by most experts as a major solution for climate change mitigation. Although it is already widely accepted in most countries, it is still an emerging concept in the Philippines. 

The good news is: Studies on blue carbon in the country are increasing steadily, although more work still needs to be done especially on seagrasses.  

“Currently, almost 80% of blue carbon studies in the Philippines are foreign-funded, ergo, it lacks local funding support,” Corcino said. “We encourage everyone, whether members of the academe, government, institutions, up to the laymen, to do their part in our fight against climate change.  

“This could be by studying mangroves and seagrasses, participating in activities for their monitoring, conservation and protection, spreading awareness on blue carbon, or supporting these actions with the necessary resources like funding, equipment, or manpower,” Corcino said. 


 “Mangroves in the Philippines have long been ‘ecologically disturbed’ by rampant cutting for timber products and massive conversion of forests into aquaculture ponds,” read the introduction and overview of the “State of the Mangrove Summit” some years back. 

Almost half of the country’s remaining mangroves were lost over the past years: from 500,000 in 1918 to 240,824 in 2010, according to Dr. Severino Salmo III, an associate professor at the University of the Philippines Diliman Institute of Biology. 

Meanwhile, the Philippines has the second highest number of seagrass species in the world. It is home to 16 of the world’s 50 seagrasses; only Western Australia has more – with 17 species.

 Dr. Fortes, who had spent most of his life in the study of various blue carbon ecosystems, said all 16 seagrass species are widely distributed from Bolinao Bay in the north, Palawan and the Cebu-Bohol-Siquijor area at the center, and Zamboanga and Davao in the south. Seagrass beds cover an estimated area of about five million hectares. 

Photos by Henrylito Tacio

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