Three-runway System Project – Pilot Study of Shellfish Reef Deployment

Airport Authority Hong Kong (AAHK) has been implementing various environmental initiatives in order to enhance biodiversity and fishery resources in the waters nearby Hong Kong International Airport (HKIA).

After seeking advice from the Advisory Council on the Environment, green groups and other stakeholders, the AA is carrying out a 1-year pilot study on using recycled oyster shells, limestone and live oysters to deploy shellfish (oyster) reefs on the newly built seawall under the Three-runway System (3RS).

Peter Lee, General Manager, Sustainability of AAHK said, “This study is beneficial in that the use of recycled shells helps to reduce waste, while also conserving the coastal environment. The pilot study will be the first of its kind on artificial seawall units in Hong Kong. If the results meet our expectations, the findings and experience gained by our study will benefit other future similar projects.”

The pilot project was carried out in collaboration with The Nature Conservancy and The University of Hong Kong. The research team collected recycled oyster shells, discarded shells of mussels and scallops from local oyster farms in Lau Fau Shan, hotels and restaurants.

The shells were then sorted at a recycling site and underwent natural weathering to get rid of any organic materials to avoid any risk of spreading diseases or parasites in the waters.

The team used the recycled shells as substrates, on which they grew live oysters and created new reefs, which were expected to provide nursery and breeding grounds for different marine organisms. Amongst all others, the shells of local Hong Kong oyster species (Magallana hongkongensis) were considered most useful for reef restoration.

Marine Thomas, Senior Conservation Program Manager, The Nature Conservancy Hong Kong, said, “The reason why we like the Hong Kong agriculture species is that it is a native species, and its shell is big and thick, which can recreate the structural complexity of reefs a lot faster.”

In June 2021, the team deployed a total of 500kg of recycled shells with the assistance of divers on around 600 m² at the northern 3RS seawall. A total of 3000 live oysters were seeded in the area.

After two months, the team took 36 samples for preliminary analysis. The oyster reefs had grown steadily, and different marine organisms were found settling on the reefs - for example, crabs, sea stars, oysters, mussels, fish eggs and fishes, and more.

Dr Bayden Russell, Associate Professor, School of Biological Science, Faculty of Science of the University of Hong Kong observed, “We are really surprised not only with the number of oysters and mussels that have settled in such a short time, but also by all of the other organisms that are starting to settle. We are finding that fish have started to lay eggs, which indicates that the population of fish in the area is also enhancing.”

The team will collate the findings after a year of the reef deployment. AAHK will then evaluate the effectiveness of the study.

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