New research produced jointly by the Swire Institute of Marine Science (SWIMS) of the University of Hong Kong (HKU) and The Nature Conservancy (TNC), published recently in the scientific journal Restoration Ecology, shows the enormous potential of restoring lost oyster reefs, bringing significant environmental benefits.
Hong Kong was once home to thriving shellfish reefs, but due to a combination of factors including over-exploitation, coastal reclamation and pollution, shellfish populations have declined drastically.
The study revealed that restoring oyster reefs along urbanised coastlines can mitigate some of the environmental problems typical of coastal development, such as damage from storm surge and loss of biodiversity.
A primary benefit that healthy oyster reefs contribute to coastal environments is their role as natural water purifiers. This new study found that, just seven square metres of Hong Kong oyster reef can filter up to one Olympic-size swimming pool of water each day.
A single Hong Kong oyster (Crassostrea hongkongensis) can filter up to 30 litres of water per hour at summer temperatures, among the highest filtration rates recorded of any oyster species.
Even more importantly, oyster reefs provide habitat and nursery grounds for many native species that are otherwise lost from Hong Kong’s shores. Another recent SWIMS study conducted in partnership with TNC found that these reefs house six times more species than bare muddy shores.
The research found over 80 species on intertidal muddy shores in Deep Bay, with 95 per cent being found in oyster reefs and almost 60 per cent being found exclusively in those reefs.
Another benefit of restored reefs is increased production of commercially and recreationally valuable fish and crabs. Further, the researchers claim that demonstration of successful restoration in one of Asia’s coastal mega-cities can also act as a model, providing evidence for the environmental and societal benefits of ecological restoration within the region.
In some parts of the world, oyster reef restoration has only been successful by transplanting juvenile oysters cultivated in hatcheries into the wild. However, this new research demonstrates that natural recruitment of oysters in Hong Kong is high, meaning that restoration can potentially be achieved without the need for hatchery-reared oysters.
In assessing 10 sites where small remnant shellfish habitats are found in Hong Kong, the study also found that large oysters (beyond one year old) are very hard to find in the wild, due to on-going harvesting pressures.
“As soon as oysters or mussels are big enough to eat, someone will harvest them,” said Ms Marine Thomas, conservation project manager for TNC in Hong Kong. “We are working with government on gaining more protection and recognition for these important ecosystems and hope to include them in the next Hong Kong Biodiversity Strategy and Action Plan (BSAP).”
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