Taiwan is home to a diversified coral ecology that is rarely seen in other subtropical areas around the world. However, as the climate is getting hotter and breaking historical records, Taiwan begins seeing widespread coral bleaching in its oceans. The Coral Reef Observation System of the National Oceanic and Atmospheric Administration (NOAA) upped the bleaching warning at the highest stress level in July and August respectively, as it means severe coral bleaching and significant mortality is underway.

A Greenpeace East Asia crew has documented a large-scale coral bleaching from Kenting since it got warning alert level 2, which is on for the entire Taiwan currently from Yehliu, Longdong in the northern part to Green Island, Orchid Island, and the Pratas Islands in the southern area.

Coral Bleaching Investigation in South Taiwan.© Yves Chiu / Greenpeace

What are the causes of coral bleaching in Taiwan? What are the impacts? And how can we prevent coral bleaching? 

What is coral?

A lot of people may have the wrong impression that a coral is a kind of “plant” growing in the sea. In fact, corals are actually animals with colonies of many identical individual polyps. Most of them are transparent. The riot of colors that we see comes from the algae called zooxanthellae that provide photosynthetic nutrients and form a symbiosis with the corals.

Taiwan used to be known as the coral kingdom. Although the coral reef communities widespread in Kenting, Green Island, and Orchid Island are less than one-thousandth of the world’s coral reefs in terms of scale, its various indeed is one-third of the world’s total. 700 species of stony corals in the globe, 250 species can be found along the coast of Taiwan!

Red coral on Wan Li Tong reef, Green Island, Taiwan.© Paul Hilton / Greenpeace

How important is coral to the ocean?

Coral is an indispensable part of the entire marine ecosystem. Coral reefs harbor many marine creatures. All manners of creatures inhabit, breed, feed, and avoid enemies in coral reefs, which naturally forms a rich ecosystem. There can be as many as 1,500 types of fish within coral reefs. That’s why it is dubbed the “tropical rainforest in the sea.”

What is coral bleaching?

Coral is the longest-lived animal, as long as the environmental conditions are good enough, it can grow for hundreds of years. Therefore, the death of coral colonies is usually due to the depressing living environment or the destruction of other creatures. 

Corals are extremely sensitive to the surrounding. Changes in environmental conditions, such as water temperatures, pH values, and turbidity will directly affect the symbiotic relationship between corals and zooxanthellae. When the living environment is not optimal, the symbiotic zooxanthellae will gradually leave the corals or be expelled by the coral, and the corals that lose their color sources will gradually bleach.

After the symbiotic algae leaves, the corals will not die immediately. If the environment becomes better, the bleached corals can regain the zooxanthellae and slowly recover for survival.   However, if they bleach for a long time, the corals will gradually weaken and die. Therefore, coral bleaching is the last distress signal for corals.

Causes of coral bleaching: global warming and human pollution

Global warming is bad for coral reef growth

With the drastic changes of climate in recent years, global warming has caused seawater temperatures to rise, and the greenhouse effect has also caused “ocean acidification” that weakened coral’s absorption of calcium carbonate. When coral reefs are not strong enough to resist natural erosion it will take longer for them to recover from bleaching. 

NOAA’s coral reef observing system uses satellites to monitor the sea surface temperature and marks areas with high water temperatures to alert the risk of coral bleaching. Due to the Pacific high this year, Taiwan has encountered fewer typhoons that lead to higher temperatures of the land and sea. The waters around Taiwan, including Pratas Islands and Taiping Island, have recorded sea temperatures of 30°C.

The optimal water temperature range for coral growth is 20-28°C. If the water temperature is lower than 18°C or higher than 30°C, most corals will expel the symbiotic algae in their body, causing bleaching or even death. If the number of typhoons in Taiwan this year is expected to stay low, the situation of coral bleaching will appear pessimistic while the sea temperature remains high. It is worth noting that short-term changes in sea temperature will not cause bleaching. The main cause of large-scale coral bleaching is often the continuous abnormal warming of the seawater.

The temperature of sea waters has continued to rise since May in southern Taiwan. This is a documentation that records coral bleaching at three diving sites in Kenting in the area in August.
© Yves Chiu / Greenpeace

Human activities are a culprit 

In addition, terrestrial and marine pollutants due to human activities can easily cause harmful impacts on coral reefs, such as agricultural pesticides flowing into rivers, industrial and household wastewater discharged into the sea, and even sunscreen products because they contain chemicals like Benzophenone and Octyl methoxycinnamate that will disrupt their reproduction and growth cycles. 

 Marine ecosystems are hit hard

The destruction and death of coral reefs has dealt a major blow to the marine ecosystem. In fact, the growth rate of corals is very slow. They only grow about one centimeter a year. Therefore, the coral reefs we see in the sea are often the results of decades or even centuries.  Once they’re damaged, they’ll need the same amount of time to resume their original size.

In addition to conserving diverse marine life, a healthy coral reef ecosystem also supports various human needs. It not only protects the adjacent coastline from ocean erosion but also has high economic values. It can generate billions of dollars in tourism revenue. Therefore, the decline of the ecosystem caused by coral bleaching will inevitably affect the livelihoods of industries that depend on coral reefs, such as tourism and fishery.

How to solve the problem of coral bleaching?

Energy-saving and carbon reduction to slow down global warming

 In the face of the unusual increase in seawater temperature caused by climate change, more ambitious carbon reduction targets should be set to replace fossil fuels with sustainable energy.   

Everyone can save the coral 

Beautiful corals provide habitat for diversified marine creatures. However, various human activities, excessive coastal development, or the unusual increase in seawater temperatures due to climate change have put great pressure on corals. As human beings get to know the importance of coral reefs, the related preservation work can be started on the individual level. 

Healthy Corals and Oceans are important to the Earth and humankind. © Paul Hilton / Greenpeace

“Coral is an indispensable part in the oceans, as it formed a convoluted ecological cycle for other species, such as a resting and reproducing area, as well as the food-finding place and avoiding dangers,” said Lena Chang, climate and energy campaigner at Greenpeace East Asia. “It’s dubbed the rainforest in the oceans because it can harbor up to 1,500 types of fish.”

“A healthy coral reef can bring upon high economic values,” said Chang. “It’s an asset to generate billions of dollars in revenues from tourism. And it protects the coastline from oceans weathering. If the entire ecology is damaged, the tourism and fishery industries will be obviously affected as well.” 

Greenpeace East Asia urged policymakers to declare a climate emergency, putting climate-related risk disclosure and carbon reduction targets on the agenda in accordance with the Paris Agreement.