Every Thursday around noon, a brown minivan pulls up in the alley behind the glitzy Peninsula hotel at Victoria Harbour in Kowloon, Hong Kong. A porter rushes out to meet it from the back door of the hotel kitchen, lugging a large white rice sack. The driver weighs the bag on a handheld scale – it’s 40kg (88lb) – then chucks it into the back of the vehicle with a surprising clank.
The van takes the sack to a recycling facility just outside the city, and tips out 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 into Hong Kong’s bays as part of a series of restored oyster reefs.
Nestled in between the South China Sea and the Pearl River Delta, Hong Kong has been seen historically as an oyster hotspot. “They have been supporting our livelihood since ancient times,” says Anniqa Law Chung-kiu, a project manager at the Nature Conservancy (TNC) in Hong Kong. “Both oysters and their shells are treasures to humans.”
Over the past five decades, however, the city’s sprawling urban development, water pollution, as well as the over-harvesting and frequent seafloor 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.
The more oyster colonies falter, the worse the problem gets: oysters are filter feeders and purify water by gobbling up impurities. Just one Hong Kong oyster can filter up to 200 litres of water a day, more than any other known oyster species. But decades of rapid industrialisation have largely halted their water-purifying services.
The depletion of Hong Kong’s natural oyster reefs also affects the ability of local farmers to sustainably cultivate their oysters in a healthy environment, denting the reputation of the city’s 700-year oyster farming tradition, designated by Unesco as an “intangible cultural heritage”.
Inhabitants of the coast feel abandoned, says Ken Cheng Wai-kwan, the community leader of Ha Pak Nai on Hong Kong’s Deep Bay, facing the commercial city of Shenzhen in China. “This place is forgotten,” Cheng says. “Oysters have been rooted here for over 400 years. I ask the question: do we want to lose it, or not?”
A group of activists and scientists are taking up 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 the oysters may make a comeback. They’ve selected locations around the island where data they’ve collected suggests ecosystems still have the potential to be rebooted, and there are still enough oyster larvae to recolonise and repopulate reefs. Ideally, this will have a positive effect on local biodiversity as a whole, and farming communities.
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 Deep Bay to recycle up to 10 tonnes of shells every year. They collect an average of 870kg every week from 12 hotels, supermarkets, clubhouses and seafood restaurants in the city, including some of its most fashionable establishments. About 80 tonnes of shells have been recycled since the project began in 2020.
Restaurants will soon be further incentivised to recycle the shells when Hong Kong introduces a new fee for waste removal – something that is routine in many countries, but only became law in Hong Kong in July and remains controversial.
“In many respects, [the recycling scheme] offers a deeper understanding of the significance of sustainability to our team members,” says Leung Shun Wai, chief steward at the five-star Peninsula. But persuading smaller enterprises 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 heaps of recycled oyster shells in selected areas 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 grow into well-structured reefs.
Preliminary data shows some of the restored reefs have started to increase the levels of biodiversity, but more research is needed to determine to what extent they are contributing to the filtering of the water, says Law.
Scientists from the City University of Hong Kong are also looking to use oyster shells to increase biodiversity on the city’s concrete seawalls. They hope to provide tiny, wet shelter spots around the seawall in which organisms can find refuge during low tide.
“It’s a form of soft engineering, like a nature-based solution,” says Charlene Lai, a research assistant on the team.
Key questions remain unanswered about the extent to which oysters can help 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 is yet to be quantified”.
There’s reason for hope though, if the project succeeds. “Oyster reefs are kind of the ugly ducklings of the coastline,” says Bayden Russell, associate director of the University of Hong Kong’s Swire Institute of Marine Science, who is running a project surveying the city’s bays to fully grasp, record and analyse the state of its oysters, and their future potential for restoration.
“But you’ll see more fish, you’ll see more crabs, more birds,” he adds. “That diversity of other organisms will be obvious.”
