Heat and salt threaten to end a tradition dating back hundreds of years. Farmers and scientists are fighting back.

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By Regina Lam

Away from the skyscraper clusters of Hong Kong’s business districts sits the weathered northern fishing village of Lau Fau Shan (Floating Mountain).

Chan Kwok Leung, known as “Brother Leung”, is a 58-year-old, sixth-generation oyster farmer. As a child he shucked oysters with his father during winters on the shore of Deep Bay where his village sits, on the eastern side of the Pearl River Estuary. 

The colder the weather, the fatter the oysters grow, farmers used to say. But chillier winters made harvesting harder. “The seawater felt icy cold and often numbed my hands,” says Chan. “It doesn’t feel like that any more.” 

Today’s subtropical Hong Kong rarely experiences the bitter cold days below 5C that Chan says he sometimes experienced while growing up in the 1970s and ‘80s.

Driven by climate change, warming, saltier water has slowed oyster growth and contributes to die-offs every year. “Super typhoons” now batter the bamboo rafts used for farming for more hours per year, pushing increasing numbers of aging growers to retire their practice.

Similar problems are plaguing those who rely on oysters in other parts of the world. The animals filter large volumes of water as they feed on microalgae, boosting water quality. Their growing shells trap carbon and create reefs that protect coasts and create habitats for other species. 

But warmer waters, shifting weather patterns and more damaging storms are straining many who farm or collect them.

Despite the hardship, Chan has not left oysters. Instead, he joined a team of scientists working to help the sector adapt and trying to revive this piece of Hong Kong’s cultural heritage, which enriches marine biodiversity. 

One solution they have been working on is to breed a “super oyster” that can better survive Deep Bay’s increasingly salty waters.

An Ancient Practice 

Historical records show an oyster business in Lau Fau Shan as early as 1667, operated by the Tang clan. Oyster farming lineages go back further still. Some farmers, including Chan’s father, migrated to the area in the 1960s from the coastal town of Baoan in Shenzhen, about 20 kilometers away, where their ancestors had farmed oysters since the Song Dynasty (960-1279).

Today, around 10,000 bamboo rafts float across Deep Bay. From each rope, dozens of oysters hang in the currents and grow fat before being harvested and sold to Hongkongers, who prize their size and flavor.

Most oysters produced here carry a local identity in their scientific name: Crassostrea hongkongensis. These are plumper and grow better in less saline estuary waters than the more common commercial species, the Pacific oyster.

Some Hong Kong oysters are sold fresh, often for hotpots or deep-fried dishes. Many others are dried along the shore before being traded in a narrow lane in the village lined with seafood stalls or dispatched to other markets in the city. 

Air-dried oysters, including both semi-dried “golden oysters” and fully dried varieties, are a beloved delicacy symbolising prosperity in Cantonese culture. During the Lunar New Year, families usually pan fry or braise them with mushrooms, vegetables and other seafood to wish for good fortune in the year ahead.

Massive Die-Offs 

For the oysters to thrive, “the winds and rains must come in good time,” Chan says. Farmers follow the traditional 24 solar terms of the Chinese lunar calendar to track seasonal changes and guide their work. “It’s a practice passed down from our ancestors,” he says.

But climate change, driven by greenhouse gas emissions, has disrupted the longstanding rhythms that earned Hong Kong oysters their loyal following. 

Traditionally, farms began to yield good harvests from the mid-autumn festival, in September or October. But recent winters have arrived later and with higher temperatures, pushing the harvest to start in January and February, shortening the previous six-month harvesting season to three months. 

Worse than poor harvests are the die-offs that increasingly occur when Hong Kong enters spring in March and April. Over a decade ago, farmers began reporting more frequent oyster die-offs, which wipe out large swathes of the farms in Deep Bay, killing oysters string by string, raft by raft. 

Farmers told Dialogue Earth that such events, which cause over 70% loss of oysters, used to hit the bay once every decade. They now strike every three to six years. Smaller mortality events, which see over 30% of oysters dying, have become an annual problem.

Scientists at the University of Hong Kong believe climate change is the likely culprit. Southern China’s temperature now spikes up earlier and faster in spring, said Thiyagarajan Vengatesen, a Professor at the university’s School of Biological Sciences. ‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬

The rainy season is also often arriving later, and does not dilute the salinity of waters in Deep Bay as it used to. This warming and high salinity, along with deoxygenation caused by nutrient pollution and limited sunlight in overcast spring, puts oysters under extraordinary stress. This leaves them more vulnerable to pathogen attacks. Once a group of oysters die, other follows, says Vengatesen. 

For farmers, this is devastating. “When you shuck the oyster, you can tell immediately something is wrong, as the flesh turns reddish,” Chan says. He still remembers vividly his first encounter with a mass mortality event in 2007. “It was unsettling. A whole year of my work was gone.” 

Die-offs of different levels of severity have happened almost every year since. Farmers now seek to harvest their shellfish before the high-mortality period and move rafts to less saline waters at the first sign of problems.

While this helps somewhat, Chan says a farmer’s life is “in the lap of the gods.”

Worse Typhoons Spell Disaster

Farmers feel even more powerless when intense typhoons hit. 

“We are seeing more super typhoons these days,” says Chan Shu Fung, an oyster grower in his 40s also from Lau Fau Shan, referring to the most intense tropical cyclones. Unlike mass-mortality incidents, “when typhoons hit right at the bay, there is nothing you can do about it.”

Last year, Hong Kong faced 14 tropical cyclones that either landed or passed close enough to trigger warnings, more than double the long-term average and the highest number in a single year since 1946.

Chan Shu Fung took over the family business when his father retired in 2014. Three years later, Super Typhoon Hato skirted Hong Kong. It was followed in 2018 by Super Typhoon Mangkhut. Together, the storms caused hundreds of injuries and billions of Hong Kong dollars’ worth of damage. 

Hato wreaked havoc on 60 operating oyster rafts that were now Chan Shu Fung’s responsibility, swallowing some half a million shellfish. After he rebuilt and reseeded nearly half of his rafts, the following summer he lost 90% of his crop again to Mangkhut.

Chan Shu Fung saw many elders in town hang up their shuckers after the storms, shrinking the scale of production in Deep Bay. At the industry’s peak in the 1960s and ‘70s, it supported around 300 oyster-farming households; today, about 70 remain, he says. 

Chan Shu Fung too thought of giving up after 2018. But he had just sunk new investment into the business after taking over from his father. “All I could do was hang in there, grit my teeth and carry on.”

Improving Survival Rates 

At his lab at the Swire Institute of Marine Science, Vengatesen is working with Chan Kwok Leung to investigate the struggles of the ancient industry and look for ways science can alleviate its modern problems. 

Vengatesen’s team of researchers have developed a way of predicting which oyster strains are more likely to survive under conditions of high salinity and other stressors, based on gene comparison and oyster survival data.

Commercial breeders can use this toolkit to analyze oyster DNA and identify parents with a better chance of surviving in the warming Hong Kong waters, which they can use to produce seeds in their hatcheries.

The team have also bred salt-tolerant shellfish themselves. Using their genomic selection technology, they have developed a more resilient animal they call the Hong Kong Super Oyster. 

This has a 30-40% survival rate in high salinity conditions, the team says, a significant improvement from the regular Hong Kong oyster’s less than 10%.  

Vengatesen aims to boost the survival rate to 80%. The more data that is entered to refine the models that predict survival, the more accurate it will become over time, he adds.

Chan Shu Fung began trialling the new strain on his rafts in September last year. “It will take a year for us to tell how good they are,” he told Dialogue Earth.  

Hemmed in By Concrete Jungle

Even if these new oysters can allow the village fishers’ traditions to continue, it is unclear how long Lau Fau Shan will remain as it is. A development project proposed by the Hong Kong government is set to transform the area into a hub for fintech, start-ups and residential buildings dubbed New Digi Bay. 

The initial proposal sparked concerns about the continuation of oyster farming. Chan Shu Fung, who frequently liaises with the government as the chair of farmers’ group the Deep Bay Oyster Cultivation Association, is hopeful though. He says the latest planning proposal pledges to conserve part of the bay and promote oyster traditions. Doing this while improving infrastructure could bring more tourists to experience its oyster culture, he hopes.

“If the urbanisation plan does not come into conflict with oyster farming and the ecosystem it depends on, it has more benefits than drawbacks,” he says.

Chan Kwok Leung fears the industry could decline further under seemingly unstoppable trends of urbanization, climate change and younger people reluctant to take up the hard life of an oyster farmer.

But he is determined to keep trying, adding modern innovations like the Super Oyster to an ancient tradition.

The forces battering Hong Kong’s oyster farms are strong, but Chan Kwok Leung cites a Chinese idiom that only gold remains after strong waves wash away the sand.

“We had our glory days,” he says. “I am trying to do something now. Hopefully, new technological breakthroughs may bring them back.” 

Featured image: The Swire Institute of Marine Science/University of Hong Kong.

This article was originally published by Dialogue Earth.

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About the author: Regina Lam is deputy ocean editor at Dialogue Earth, based in London. She joined in 2021 and has worked at major Hong Kong newspapers and has reported for the BBC World Service. She holds an MSc in global affairs from King’s College London. Regina is interested in global ocean governance, environmental justice and what makes compelling storytelling and robust investigation in environmental journalism. She speaks Cantonese, Mandarin and English.