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Bamboo reefs to feed sturgeon in ‘desert’
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BIOLOGISTS are creating an “ocean pasture” by building bamboo reefs on the seashore of Shanghai’s Chongming Island, attracting a wide range of marine life to sustain endangered Chinese sturgeon and lure back large fish.
Planting seeds and trees fights the encroaching desert in China’s north and west, while scientists battle marine “desertification” — loss of biodiversity — by planting bamboo poles and spreading aquatic organisms in intertidal zones.
“Shanghai, located in the Yangtze River estuary, is definitely facing marine desertification and loss of species,” says Liu Jian, director of the department for sturgeon protection in the Shanghai Yangtze Estuary Nature Reserve.
The estuary is known as the sturgeon’s “kindergarten” where juveniles spend time before heading out to the ocean for two years. Scientists have been monitoring marine life in the estuary, including around Chongming Island (County) since 2004 and have documented the degradation of the environment.
And they are trying to revive it.
From 2012-13, scientists created an artificial marine habitat, the beginnings of a reef that they call an ocean pasture on the eastern shore of Chongming. The pasture, with a reef skeleton of bamboo poles, covers 256,000 square meters and has already attracted a range of aquatic life, from algae and plants to clams, barnacles, worms, shrimp, hairy crabs and small fish.
Because of pollution and human development, marine animals have almost disappeared from the estuary.
It is hoped that the creatures gathering around these hollow, perforated poles, will eventually come together and form a living reef that provides food for larger fish, such as the rare and costly daoyu or knife fish.
Already they are gathering and slowly reefs are forming.
“The reefs are working as expected, but it’s far from enough,” says Chen Jinhui, deputy director of the nature reserve department protecting the sturgeon.
The next phase of the project will be launched this month on Chongming, covering an additional 400,000 square meters with bamboo poles and introducing more marine life. The design may be changed and horizontal pieces may be added.
The Yangtze River estuary is important in the life cycle of the endangered Chinese sturgeon, which breeds in the upper reaches. The estuary is where mature fish fill up on food and prepare for their journey upstream.
Twenty years ago, the estuary used to be full of Asian clams, razor clams, shrimp, crabs and other marine animals that sturgeon feed on. A survey in 2010 showed that in each 10 square meters on the eastern shore there was not a single small marine animal, known as benthos.
Today the Chinese sturgeon that used to feed only on shrimp and crabs are now eating anything, including leaves and roots, says Chen, the sturgeon expert.
“That’s very sad. It means that regardless of all our efforts to save the sturgeon, we cannot protect them from extinction if they cannot find food in their natural habitat,” he says.
To address the problem, scientists launched the “ocean pasture” project in 2012, after extensive studies.
Though the idea for tackling ocean desertification is not new, this reef project is believed to be the first launched in an estuary anywhere, according to Chinese scientists.
The different sand quality, water currents and human activity make estuary regeneration very different from reef creation in the ocean, where China also creates reefs.
The Chongming intertidal zone, which is covered during high tide, is known locally as tie ban sha because it’s packed hard. Other common approaches, using cement structures and broken ships, were ineffective and were easily washed away or buried. There was no way they could attract marine life and thus form a reef in the estuary.
“All those structures were partially buried on the second day and disappeared on the third day, regardless of their shape,” Chen says. “A heavy reef structure cannot work here.”
The idea of a bamboo reef to attract fish occurred to Chen when he noticed that barnacles had collected on a timber pole used to moor fishing boats.
Instead of using carefully designed artificial reefs, scientists used rows of simple, 2.3-meter bamboo poles inserted deep in the sand and extending 50cm above the water at high tide. They are placed every 1.5 meters.
The light poles soften the sand in a 15cm radius and create a perfect habitat for benthos that eventually merge between the poles, Chen says.
“Rows of bamboo poles can help create broader habitats and improve biodiversity in a larger area without reefs,” he says.
In an early trial, his team inserted around 100 bamboo poles and found that within a week, large numbers of benthos were gathering. Biologists worked out the best layout and design so these future reefs could survive even typhoons.
In late 2013, they introduced around 200 tons of small organisms, including Asian clams, marine clams, worms and other life, to accelerate the process and lure more animals to the poles.
It seems to be working.
A study in late April found that on average more than 100 benthos gathered around each pole, compared with only 10 before they were introduced. The poles were anchored securely. In the same area scientists also found shrimp and hairy crabs, which they had not introduced. In nearby areas without poles, they also found more estuary life.
The Chinese sturgeon used to breed in November in 20 areas upstream, but they were blocked by dam and other construction. They adapted and found one new area. Last year, no sturgeon were detected in that area by the Ministry of Agriculture — it was the first time none of the great fish was spotted in more than 30 years of surveys.
And if no juvenile sturgeon are found in the estuary this year, from May through October, it will be bad news: virtually no newborn sturgeon.
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