Restoring oyster reefs would produce major benefits

The restoration of oyster reefs could lead to enormous environmental benefits, according to a new study led by the University of Hong Kong. Restoring lost oyster reefs would help mitigate some of the destruction associated with coastal development, such as damage from storm surge and biodiversity loss.

Shellfish reefs were once abundant along the shoreline of Hong Kong. A number of stressors, including over-harvesting and pollution, has caused shellfish populations to drastically decline. 

“Globally, we have lost 85% of shellfish reefs, making it the most endangered marine habitat on earth,” said study co-author Marine Thomas. “Most people associate oysters with food, but less well-known is that oysters create reef habitats that support coastal marine life. Only by restoring these lost habitats can we start to bring back some of the associated environmental benefits.”

The experts report that just seven square meters of oyster reef can filter enough water to fill up an Olympic swimming pool each day. A single Hong Kong oyster can filter up to 30 liters of water per hour at summer temperatures. This is one of the highest filtration rates of any oyster species.

Oyster reefs also provide habitats for many native species that are otherwise lost. In a recent study from the Swire Institute of Marine Science (SWIMS), researchers found that these reefs house six times more species than bare shores. 

Out of more than 80 species that the team identified along the muddy shores in Deep Bay, 95 percent of them were found in oyster reefs, and almost 60 percent of those species were found exclusively in those reefs.

“A previous SWIMS study found that Hong Kong is home to approximately 6,000 marine species and 26% of all marine species in China. This new research adds to that list, as we’ve identified a small crab previously not seen in Hong Kong. This shows us just how understudied these ecosystems are,” said Dr. Bayden D Russell.

Restored reefs also increase the production of commercially and recreationally valuable fish and crabs. According to the research, oysters could be naturally recruited in Hong Kong, which would eliminate the need for transplanting the shellfish from hatcheries. 

“We were excited to find high natural recruitment levels which suggests that oyster reef restoration is possible without hatchery intervention,” said Dr. Russell. “We think that this recruitment is because traditional oyster farming in the Pearl River Delta has maintained populations of native oysters in the system in spite of the loss of oyster reefs and these farms could potentially act as a source of larvae.”

Across ten different sites that were examined for the study, the team found that large oysters beyond a year old were very hard to find due to overharvesting.

“While we are excited by the biological feasibility of restoration, unfortunately the human aspect remains our biggest challenge to bring these habitats back at scale. Shellfish habitats are still severely under protected in Hong Kong, with very little public awareness of their ecological value,” explained Thomas.

“Wild harvesting is a huge problem – as soon as oysters or mussels are big enough to eat, someone will harvest them. 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.”

The study is published in the journal Restoration Biology.

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By Chrissy Sexton, Earth.com Staff Writer