Oysters help clear the waters in Hong Kong

September 27, 2022

HONG KONG – Recycling campaign and artificial reefs result in series of benefits

Few Hong Kong residents are aware that numerous oyster reefs are turning murky waters crystal clear at a seawall under the newly reclaimed third runway at the city’s airport.

An “underwater zoo” of marine life has formed in waters around these reefs. Baby oysters and fish eggs can be found, while crabs, starfish and mussels burrow in the reefs, surrounded by shoals of fish.

These reefs are not natural, but are artificially formed.

In June 2021, on instructions from the Airport Authority of Hong Kong, a team of divers placed reefs comprising 500 kilograms of discarded oyster shells seeded with 300 live oysters under a 600-square-meter area of the northern third runway seawall.

It was the first oyster restoration project launched on artificial seawalls in the city to improve water quality and biodiversity close to Hong Kong International Airport.

Successful implementation of the project is largely due to The Nature Conservancy, or TNC, a global nongovernmental environmental organization working on conservation in more than 70 countries and regions.

The project spread word about oysters’ ability to restore ecology in Hong Kong — bringing an “oyster reef restoration model “to the city. The recycled shells used by the airport authority were provided by TNC.

Anniqa Law Chung-kiu, conservation project manager for TNC Hong Kong, said that although the city has a 700-year history of oyster farming, many residents knew little about the benefits of oysters and oyster reefs when the project was launched.

The project was a new idea for Law, who worked in marine conservation for seven years before TNC launched its oyster reef restoration project in Hong Kong in 2016.

The reefs positioned near the airport work by allowing dense clusters of live oysters to grow around the shells of dead oysters.

One of the city’s favorite seafoods, oysters are also natural filterers, with just one oyster capable of filtering 200 liters of water per day. Marine experts even refer to oysters as “ecosystem engineers”.

Oyster shells can be recycled for use as natural materials, and are a perfect surface for reefs to grow on.

The oyster reefs also filter water, creating a healthier environment for marine life. These reefs — habitats for species such as seagrass, horseshoe crabs and shore birds — help increase biodiversity. In addition, they enhance coastal defenses against storms, and stabilize shorelines.

However, oyster reefs are now some of the most endangered habitats on Earth, as the oyster population has fallen significantly due to overexploitation, coastal reclamation, pollution and the decline in farming, among other factors.

Law said, “Eighty-five percent of oyster reefs globally have disappeared over the past 150 years.”

Many countries have taken action to save these reefs.

In the United States, two educators founded the Billion Oyster Project in 2014, a nonprofit organization based in New York City aimed at restoring a billion oysters to New York Harbor by 2035. To date, some 75 million have been restored.

In addition, TNC has launched oyster restoration projects in more than 150 countries, including Australia and New Zealand. It began efforts to restore the oyster population in Hong Kong in 2016.

This work was not easy. When Law and her team started the project, they could not find any data about the city’s oyster reefs, related studies at local universities and research institutes, or news about previous oyster restoration activities in Hong Kong.

However, the situation quickly improved with help from the local community. In the next few years, residents from all walks of life, the government, university research institutes and volunteers offered their help.

Risk avoidance

TNC recycles oyster shells through voluntary work, the catering industry and oyster farmers.

The recycled shells are taken to a site in Ha Pak Nai village, Yuen Long, where they undergo natural weathering to get rid of organic materials — avoiding the risk of spreading disease or parasites in the sea.

The cleaned shells are placed in the sea in batches to act as surfaces for young oysters to grow on.

Recycling the shells is the basis for subsequent work. As many shells are left on the beach, TNC launched a volunteer campaign in late 2019, calling for residents to collect these shells.

Once or twice a month, 20 to 40 volunteers led by Law visited Lau Fau Shan, Hong Kong’s best-known oyster-raising site, or Pak Nai, a wetland area renowned for its rich biodiversity, to gather reefs and abandoned shells.

Many residents volunteered for this work, including Jonathan Chan Pok-chi, who did so on a friend’s recommendation.

Chan, who heads a local nongovernmental fishing organization, led some 20 members on a visit to Lau Fau Shan on July 23. This day, the hottest of the year according to the Chinese lunar calendar, is known as dashu, which translates as “major heat”.

The volunteers removed Spartina alterniflora, an invasive cordgrass that turns wet mudflats into dry land along the beach. They gathered discarded oyster shells, selecting those to use. They also got rid of mud on the abandoned natural reefs.

At 11 am, wearing rubber boots, Chan stepped into the wetlands under a scorching sun. He was unable to move, as when he stood upright, his knees were submerged in mud, and he was sinking into the mire.

The volunteers then decided to stand at arm’s length from each other, forming a line to pass along the shells and reefs one by one, with the person at the end of the line placing them into bags.

Drenched in sweat, they ended their work at 5 pm. Chan, freed from the mud, drank three liters of water throughout the day, with his clothes covered in dirt. “But it was worth it,” he said.

When passing the reefs, he saw small crabs burrowing — immediately realizing the significance of this activity.

He said: “A single spark can start a prairie fire, and small actions by each person, when combined, will generate great power. Lau Fau Shan is near Shenzhen Bay, and if its environment is protected, it will benefit economic development and environmental conservation throughout Shenzhen.”

By the end of July, more than 7,600 people had taken part in activities related to the restoration project. They gave talks to audiences, held events to promote oyster reefs, or joined work to recycle shells from the beach, according to Law.

Waste crisis

Last year, Hong Kong ranked second for seafood consumption in Asia and eighth in the world. However, Law said, “Most discarded shells were treated as garbage by the food and beverage industry, ending up in Hong Kong’s landfills.”

In 2020, food waste took up the largest share — more than 30 percent — of the 10,809 metric tons of solid municipal waste each day in Hong Kong. That year, the city’s per capita municipal solid waste disposal rate per day rose to 1.44 kilograms, up from 1.27 kg in 2011.

As Hong Kong’s three landfills are expected to be full by the 2030s, and local land supply is precious and limited — making it hard to build more landfills, the city faces a huge waste crisis.

In August 2020, TNC launched Save Our Shells, a project aimed at recycling discarded shellfish shells from the local catering and oyster farming industries.

Law phoned and visited many local hotels and restaurants, including Cordis Hotel, a five-star establishment in Mongkok.

Paul Mcloughlin, culinary director of Cordis Hong Kong, who comes from Canada and has lived in Hong Kong for 14 years, was surprised when Law approached him to discuss oyster shells.

“I knew a little about the benefits of oysters, but this was the first time I had learned about their advantages in such a comprehensive way,” he said.

Touched by Law’s passion, and eager to contribute to the environment, Mcloughlin’s team partnered with TNC. Cordis Hotel was the first enterprise to join the project.

With no experience to draw on, the team members designed a recycling system. They bought dozens of buckets, printed “Save Our Shells” in green on the outside of them, and placed one bucket on each dining table at the hotel.

Signs were positioned beside each bucket, introducing the shell recycling project and advising customers to place their discarded oyster shells in the buckets.

After each meal, waiters placed the discarded shells in a bin, before they were washed, sterilized and packed in bags by kitchen staff members. The bags were placed in a room at the hotel to await collection by TNC representatives twice a week.

In November 2020, the hotel first tried recycling in its European-style restaurant and bar that specializes in seafood. Each week, up to 50 kg of oysters was recycled.

After becoming more familiar with the process, the hotel tried the recycling process in its buffet restaurant in August last year.

The hotel’s recycling rate was more than 50 percent, with an average of 200 kg of oyster shells recycled every week. It recycled 6.2 tons of shells from October 2021 to July, even though it was closed for three and a half months due to the COVID-19 pandemic.

Mcloughlin was proud that food waste was reduced during this process, and that the hotel enabled thousands of customers to learn about oyster recycling.

The hotel footed all costs for recycling on its premises, such as human resources, storage space, and production of materials.

“I have lived in Hong Kong for 14 years, and it is my second hometown. I feel an obligation to take responsibility for protecting the city’s environment,” Mcloughlin said.

He called for more restaurants to recycle oyster shells, as by doing so, they can help consolidate resources, share transportation costs and educate consumers.

Eleven outlets in the local restaurant industry had taken part in the Save Our Shells project by the end of July, with TNC receiving five or six calls from restaurants each month to learn about the recycling project, Law said.

Joint efforts

Chan Shue-fung, head of the Deep Bay Oyster Cultivation Association, was born to a family with a history of more than 50 years in raising oysters. In 2014, he inherited the family oyster farm at Lau Fau Shan from his father. Four years later, Law approached Chan about recycling the oyster shells.

Chan’s family members recycled such shells several years ago, but for commercial purposes. They ground the shells into powder and sold them as soil additives or fertilizer supplements. Chan stopped this practice when it was no longer lucrative — later restarting it to protect the environment.

He began recycling shells for TNC. After the oysters matured, he removed the meat to sell it, collected the shells, and sent them to his farm for twice-monthly collections by TNC.

For a year, his farm produced about 8 tons of oysters and provided some 3 tons of shells to TNC. With the emergence of the pandemic, oyster production at the farm fell, but Chan still saved the shells for TNC, and called on members of his association to join the recycling effort.

With the help of local communities, as of July 21, TNC had collected 25.2 tons of discarded oyster shells, with 3.1 tons gathered by volunteers, 19.7 tons from restaurants, and 2.4 tons from oyster farmers.

About 21 tons of oyster shells have been placed on the seabed in four TNC projects.

The organization’s first pilot reef was launched in Lau Fau Shan in May 2018 in partnership with the Swire Institute of Marine Science at the University of Hong Kong, or SWIMS. A year later, TNC introduced its second pilot reef at Tolo Harbour in the New Territories.

Working with the airport authority, TNC conducted the city’s first oyster restoration project on Lantau Island, west of Hong Kong Island, in June last year. It also initiated a new restoration plan in Tolo Harbour in June.

In addition, TNC is talking to key players in the Guangdong-Hong Kong-Macao Greater Bay Area about introducing the oyster recycling project to coastal areas of the Chinese mainland.

After observing the pilot reef in Lau Fau Shan, SWIMS found that an oyster species from Hong Kong with the scientific name Crassostrea hongkongensis can filter up to 30 liters of water an hour in summer temperatures, among the highest filtration rates recorded from an oyster species.

SWIMS also found that more than 80 marine species are growing around the pilot reef in Lau Fau Shan, including fish, shrimps and crabs. Some 60 percent of these species, although not newly discovered, can only be found at TNC’s pilot reefs in Hong Kong.

A tiny crab, Nanosesarma pontianacense, which is mainly found on Indian Ocean shorelines, was also recorded in Hong Kong for the first time by SWIMS on the pilot reef.

The airport authority said it is considering further expanding the pilot study and introducing more oyster reefs in local waters.