February 27, 2024

EThursday around 12:00 a brown minivan pulls up in the alley behind the glamorous Peninsula Hotel at Victoria Harbor in Kowloon, Hong Kong. A porter rushes out to meet it at the back door of the hotel kitchen, dragging a large white bag of rice. The driver weighs the bag on a hand scale – it’s 40 kg (88 lb) – then tucks it into the back of the vehicle with a surprising thud.

The van takes the bag to a recycling facility just outside the city, and reveals the contents: not rice, but hundreds of oyster shells. They will lie in the sun for a year to ensure any rotting flesh and bacteria are destroyed, before being reintroduced to Hong Kong’s bays as part of a series of restored oyster reefs.

Located between the South China Sea and the Pearl River Delta, Hong Kong has historically been seen as an oyster hotspot. “They have supported our livelihood since ancient times,” says Anniqa Law Chung-kiua project manager at the Nature Conservancy (TNC) in Hong Kong. “Both oysters and their shells are treasures for humans.”

oyster shell lying on the serabed
The shells are put back into the sea to create a substrate for oyster larvae. Photo: TNC

However, over the past five decades, the city’s sprawling urban development, water pollution, as well as overharvesting and regular seabed dredging by the lime industry – which uses the crushed shells to make construction material – have destroyed Hong Kong’s oyster habitats and made the waters less hospitable for biodiversity made.

The more oyster colonies falter, the worse the problem becomes: oysters are filter feeders and purify water by swallowing impurities. Only one Hong Kong oyster can filter up to 200 liters of water per day, more than any other known oyster species. But decades of rapid industrialization have largely ceased their water purification services.

The depletion of Hong Kong’s natural oyster reefs is also affecting the ability of local farmers to grow their oysters sustainably in a healthy environment, damaging the reputation of the city’s 700-year oyster farming tradition, designated by Unesco as an “intangible cultural heritage”.

Residents of the coast feel abandoned, says Ken Cheng Wai-kwan, the community leader of Ha Pak Nai on Hong Kong’s Deep Bay, which faces the commercial city of Shenzhen in China. “This place is forgotten,” says Cheng. “Oysters have been rooted here for more than 400 years. I ask the question: do we want to lose it, or not?”

A group of activists and scientists are taking on the challenge by collecting discarded oyster shells and recycling them to rebuild some of the reefs that have been destroyed and forgotten in the hope that the oysters can make a comeback. They chose places around the island where data they collected suggests that ecosystems still have the potential to be recharged, and there are still enough oyster larvae to recolonize and repopulate reefs. Ideally, this will have a positive effect on local biodiversity as a whole, and farming communities.

farmers pick oysters
Oyster shells are also collected from farmers for recycling. Photo: TomChan/TNC

Farmers from Ha Pak Nai were among the first to hand over their discarded shells to the TNC team for recycling. Law’s team works with eight oyster farmers from Diep Bay to recycle up to 10 tonnes of shells each year. They collect an average of 870kg per week from 12 hotels, supermarkets, clubhouses and seafood restaurants in the city, including some of its most fashionable establishments. Around 80 tonnes of shells have been recovered since the project started in 2020.

Restaurants will soon be further incentivized to recycle the shells when Hong Kong introduces a new fee for waste disposal – something that is routine in many countries, but only became law in Hong Kong in July and stay contentious.

Anniqa Law Chung-kiu holding a box of oysters
Anniqa Law Chung-kiu: ‘Both oysters and their shells are treasures for people.’ Photo: The Nature Conservancy

“In many ways, [the recycling scheme] provides a deeper understanding of the importance of sustainability for our team members,” said Leung Shun Wai, General Manager at the five-star Peninsula. But persuading smaller businesses to join the project is complex; separating oyster shells takes extra time and requires storage facilities.

So far, shells have been used in four projects, including a restored reef in the east and one near the city’s airport island. The team recreates the reefs by placing piles of recycled oyster shells in selected parts of the bay to create a substrate for oyster larvae – and other marine organisms such as sea sponges – to settle in, make a home in the nooks and crannies and grows in well-structured reefs.

Preliminary data shows the restored reefs have started to increase levels of biodiversity, but more research is needed to determine the extent to which they contribute to the filtration of the water, says Law.

Scientists from the City University of Hong Kong also want to use oyster shells to increase biodiversity on the city’s concrete seawalls. They hope to provide small, wet shelters around the seawall in which organisms can find shelter during low tide.

“It’s a form of soft engineering, like a nature-based solution,” says Charlene Lai, a research assistant on the team.

Bayden Russell and a colleague, Marine Thomas, study oysters in Hong Kong.
Bayden Russell and TNC’s Marine Thomas study oysters in Hong Kong. Photo: Edges of Earth/Adam Moore

Key questions remain unanswered the extent to which oysters can helping to restore ecosystems along Hong Kong’s heavily developed coast. A review of oyster reef restoration projects around the world suggests that while biodiversity can be improved, “The time to full recovery has yet to be quantified”.

However, there is reason to hope if the project succeeds. “Oyster reefs are kind of the ugly ducklings of the coastline,” says Bayden Russellco-director of the University of Hong Kong’s Swire Institute of Marine Sciencewhich runs a project that surveys the city’s bays to fully understand, record and analyze the condition of its oysters and their future potential for recovery.

“But you’ll see more fish, you’ll see more crabs, more birds,” he adds. “That diversity of other organisms will be evident.”

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