In the shallow sea, beyond the vibrant coral and schools of fish, you may also catch a glimpse of green along the seafloor. These plants, growing at the boundary between land and sea, are seagrasses. They may seem inconspicuous within the marine ecosystem, yet they play an extraordinarily important role in carbon reduction, ocean ecology, and even our daily lives.
High Efficiency, Vast Extent: Blue Carbon Emerges as a Key Carbon Sink
As the world moves toward net-zero carbon emissions, the role of nature's "carbon storage vaults" — which absorb and store carbon dioxide — is indispensable. Depending on the type of "vault," these are divided into three broad categories: green carbon, yellow carbon, and blue carbon. Green carbon refers to terrestrial plants such as forests and bamboo groves that absorb and store CO₂; yellow carbon broadly refers to soils, including farmland, black soil, and permafrost; blue carbon encompasses the organisms found in estuaries and oceans that store carbon, exemplified by the so-called "Blue Carbon Big Three": mangroves, salt marshes, and seagrass beds. Blue carbon has attracted significant attention in recent years because its carbon sequestration efficiency surpasses both green and yellow carbon, and because the majority of Earth's surface is covered by water and ocean, making carbon storage in the seabed more stable. This article focuses on seagrass beds — one of the Blue Carbon Big Three — exploring their carbon sink benefits, their ecological contributions, and the crises they now face.
The Ocean's Indispensable "Meadows"
Seagrasses are flowering plants that live in shallow coastal waters. Unlike the algae commonly found attached to rocks, seagrasses have roots, stems, and leaves; their roots anchor firmly in the sediment to absorb nutrients, and they also carry out photosynthesis. Seagrasses play a vital role in coastal ecosystems — they are not only habitat for numerous marine organisms, but also a food source for sea turtles, dugongs, and other marine life. Like the "meadows" of the ocean, they underpin shallow-water ecosystems.
Beyond serving as critical habitat and a source of nutrients for marine life, when seagrass beds reach a sufficient scale they form a natural breakwater along the coast, reducing the height and force of waves and thereby helping to prevent coastline erosion. The root systems of seagrasses stabilize sediments, making them an important frontline defense that protects coastal communities from the impacts of flooding.
Research has also revealed that seagrass beds offer exceptionally high carbon-reduction benefits. Their carbon sequestration efficiency is 40 times greater than that of terrestrial forest soils. The U.S. National Oceanic and Atmospheric Administration (NOAA) notes that seagrass beds store carbon at a rate 3 times higher than tropical rainforests and 10 times higher than terrestrial grasslands.
A 7% Annual Loss: Seagrasses Face a Disappearing Crisis
Although seagrasses represent just a small part of the ocean, they hold an irreplaceable position for marine ecosystems, the climate, and society. In recent years, however, seagrasses have been facing multiple crises. Research indicates that before 1940, seagrass meadows were disappearing at a rate of roughly 0.5% per year, but since 1990 that rate has accelerated to 7% per year — a level of severity comparable to tropical rainforests and coral reefs. One driver is rising sea temperatures caused by global warming: between 2010 and 2011, a marine heatwave struck Shark Bay in Australia, causing large-scale die-offs of 1,000 km² of seagrass beds and releasing 9 million tonnes of CO₂ into the atmosphere. Subsequently, heatwaves in Western Australia also caused seagrass die-offs in that region, further depriving local dugong populations of their food source.
Another crisis threatening seagrass comes from human development and pollution. Distinguished Professor Lin Hsing-Juh of the Department of Life Sciences at National Chung Hsing University has pointed out that Taiwan may have already lost as much as one-third of its seagrass. Seagrasses are highly sensitive to environmental changes; turbid water quality alone can prevent photosynthesis and cause die-offs. Many seagrass-bearing areas in Taiwan — such as Kenting and Penghu — have seen their seagrass environments degraded due to port construction, coastal development, and related disturbances. By contrast, the seagrass communities at Dongsha Atoll have remained comparatively stable due to lower levels of human disturbance.
Seagrass Conservation and Its Challenges
In recent years, the importance of seagrasses has gradually gained recognition. In 2020, seagrass bed ecosystems were formally incorporated into the Global Biodiversity Framework and the Convention on Biological Diversity (CBD). Taiwan's Ocean Conservation Administration (OCA) also issued Seagrass Restoration Guidelines last year. The restoration principles outlined in the guidelines include "prioritizing the protection of existing seagrass beds," "eliminating the factors driving seagrass decline," and "creating favorable conditions to support seagrass bed recovery." Through these guidelines, governments and organizations can tailor their seagrass restoration efforts to local conditions. The Fisheries Research Institute under the Ministry of Agriculture has also achieved results in Penghu seagrass restoration through vegetative (asexual) propagation techniques.
Nevertheless, many technical challenges still need to be overcome. Professor Lin notes that current knowledge of seagrass remains insufficient, making it difficult to fully understand the light, temperature, and other conditions required for their growth. Hsu Chia-Min, an assistant researcher at the Eastern Fisheries Research Center of the Fisheries Research Institute — which oversees seagrass restoration on the main island — has also pointed out that the number of seedlings available for restoration in Taiwan is still inadequate, and that if coastal development and pollution continue, restoration efforts may deliver diminishing returns.
As stated in the Seagrass Restoration Guidelines: "Seagrass restoration should not be regarded as compensation for or a substitute for coastal development, nor can it replace the protection of healthy habitats. Truly sustainable restoration should prioritize improving environmental conditions and addressing the root causes of decline, so as to facilitate the natural recovery and expansion of seagrass beds." The importance of seagrasses to ecosystems, the climate, and humanity alike reveals how deeply interconnected species are with one another. At a moment when environmental crises have become an ongoing reality, we must rethink how the relationship between people and the environment can become healthier and more sustainably symbiotic.
References
- Mongabay, Why saving seagrass meadows could help save the world's coastlines
- NOAA, Understanding blue carbon
- PNAS, Accelerating loss of seagrasses across the globe threatens coastal ecosystems
- 中央社, AI淨零／台灣1/3海草床消失無性繁殖之外更待播種復育| 生活 | 中央社 CNA
- 海洋保育署, 海草復育指引
※ This article is reprinted from the Delta Electronics Foundation Low Carbon Life Blog: Are the "Meadows" of the Ocean Disappearing? Why Seagrass Beds Matter for the Climate, co-produced by BlueTrend.
