Through the documentary City of Shells, Marine Thomas and her team highlight the near-total disappearance of wild oyster reefs in Hong Kong. These essential ecosystems, which once filtered water and supported coastal biodiversity, also played a significant role in the region's economic and architectural history. As the conservation lead at The Nature Conservancy in Hong Kong, Thomas advocates for their protection and reintroduction.
A Franco-Hongkonger Committed to the Ocean
You were born in Hong Kong. What led you to focus on marine conservation?
I was born and raised in Hong Kong, immersed in both French and Hong Kong cultures. My love for nature has been with me since childhood. At 13, I began scuba diving, which truly ignited my passion for the ocean. After several years in the luxury industry, I decided to start anew and work in conservation. Today, I lead the conservation team at The Nature Conservancy in Hong Kong.
A Millennia-Old Story Submerged
Why are oyster reefs central to your efforts?
Because they are both essential and forgotten. People often think of oysters as food, but they are ecological pillars. They filter water, absorb excess nutrients, promote biodiversity, and stabilize coastlines. Historically, oyster reefs covered the entire coast of Hong Kong, especially in North and South Lantau. They also played a major historical role: their shells were used to produce lime, essential in constructing the walls of Macau and even in Hong Kong.
What happened to these reefs?
Like in many large coastal cities, they were overexploited and destroyed by urbanization and pollution. Today, 85% of oyster reefs have disappeared worldwide, and in Hong Kong, it's almost a functional extinction. We've forgotten that they once formed real reefs, comparable to coral reefs, but in estuaries.
City of Shells: A Project of Memory and Future
How did the documentary City of Shells come about?
It's a project born in the field. We were exploring the seabeds of South Lantau, searching for traces of ancient reefs, when filmmaker Mike Sakas joined us. For three years, he documented our fieldwork, discoveries, and partnerships with local oyster farmers and researchers. The film traces this scientific and human adventure and sheds light on a forgotten ecological story.
What does the film specifically show?
The film outlines the steps of a pioneering restoration program. We started by identifying former reef areas using old maps and scientific data. Then we conducted diving expeditions, often blindly. We restored a pilot reef near Hong Kong Airport in partnership with the Airport Authority and observed the first signs of colonization by oysters and other marine species.
Restoring an Ecosystem Means Recreating a Chain of Life
How do you restore an oyster reef?
It's a long and complex process. It's not just about placing shells at the bottom of the water. First, we need to rebuild the reef structure, then reintroduce oysters, often by purchasing juveniles from local oyster farmers or raising them in laboratories. In South Lantau, we're fortunate to still have wild larvae in the water: sometimes, simply placing a hard substrate is enough for them to settle naturally.
Why are these efforts so important for biodiversity?
Because oysters play a foundational role in the ecosystem. They are natural filters that improve water quality and habitat builders. Their presence supports an entire food chain: worms, crustaceans, fish, birds... A healthy reef is a hotspot of marine life and also serves as a natural defense against coastal erosion.
Taking Action Now
What message do you convey through this film?
The message is clear: we must protect and restore these ecosystems before it's too late. The film supports our awareness campaign and advocacy within the public consultation on the Biodiversity Strategy and Action Plan (BSAP). We are calling for official recognition of oyster reefs as a priority marine habitat and for the expansion of marine protected areas in Hong Kong.
Do you have the necessary support?
We have partners, scientists, and even companies like Hermès supporting us. The real challenge today is administrative hurdles: access to marine areas, lack of regulatory frameworks. We need an ambitious political vision. But every citizen can make their voice heard. The public consultation is open until July 11. This film is an invitation to act.
The documentary City of Shells is available on The Nature Conservancy's website and is part of a campaign to protect oyster reefs. The BSAP public consultation is open until July 11.
For more information and to watch the documentary, please visit The Nature Conservancy's website.
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