By Christy Choi
When people think of Hong Kong, they usually picture the city’s imposing skyline. But less well known, perhaps, is Hong Kong’s equally impressive underwater architecture.
In fact, the waters off the city’s coast contain more than 90 species of hard corals – more than the Caribbean. This aquatic environment provides an unrivalled opportunity for scientists to study how corals react to pollution and other human threats.
In particular, scientists are trying to learn from what was once one of the city’s most polluted expanses of water, Tolo Harbour in north-western Hong Kong. In the 1970s, the construction of a large residential project in Tolo Harbour caused a slew of human-generated pollutants to enter the water.
“That massive development really crushed corals in inner Tolo,” says David Baker, assistant professor at the University of Hong Kong’s School of Biological Sciences.
But more recently, Baker and his team have been reintroducing corals into parts of this 10-kilometre stretch of water to see if the environment has improved enough for them to grow again.
“They have not only survived, but some of them have appeared to thrive, growing as fast as any coral in the tropics would,” Baker says.
“We started off with coral fragments like this,” he says, holding up his index finger. “And in a year they were like this,” he continues, stretching out his entire hand. “That’s 1,100 per cent growth in one year. It’s impressive.”
Globally, coral reefs are facing a greater threat than ever from climate change and human development. The World Wildlife Fund estimates that roughly a quarter of coral reefs worldwide are damaged beyond repair, with another two thirds under serious threat.
Earlier this year, Australia’s Great Barrier Reef experienced some of the worst bleaching in its recorded history. Around 8,000 kilometres of the reef have been severely damaged.
Restoration work on the Great Barrier Reef is probably impossible, because of its size, Baker says. But reef restoration in a place like Hong Kong could have a substantial ecological impact.
“Increasing the coral area by even a small fraction of a per cent would be a major increase in habitat for other species, like fish and crustaceans,” he says.
The team hope their findings might also be useful across the border in mainland China. “With coastal development in China, they’re taking about a New Great Wall, because most of China’s coastline is now artificial,” Baker says.
One of the reasons China is building new coral reefs is to help guard against storms and flooding, he adds, since it is cheaper than building artificial breakwaters.
“Corals will grow and reproduce, mangroves will grow and reproduce. They’re constantly building these sea walls. The amount of energy these ecosystems can absorb and dissipate from storms and surge is massive.”
Reefs reduce wave energy by an average of 97 per cent, according to a 2014 study published in the scientific journal Nature.
The same study showed the median cost for building artificial breakwaters was 19,791 US dollars per metre, compared to 1,290 dollars to restore a metre of coral reef.
So far, global coral restoration has been a haphazard affair consisting of a smattering of grassroots efforts that often do not follow any scientific method.
“You really need to study what kind of coral community will benefit that area,” says Samantha Lee, WWF Hong Kong’s conservation manager for oceans. “Look at the fish species and invertebrates that are found there and how the corals would benefit them.”
Staghorn corals, for example, branch out and create hiding spaces that can be used by young fish, she says.
The health of coral can be affected by everything from water flow to pollution, temperature, pH levels and the presence of sea urchins, according to Lee.
Baker and his team are studying the effects of pollution, sequencing the coral genome and studying the ecological history of Hong Kong’s seabed by using a method called coring, in which they insert hollow rods into the seabed to find out more about the ecology of the sea floor.
Studying the effects of pollutants will help them to identify places with good enough quality water for coral restoration to occur, and sequencing the coral’s genome will help them identify which genetic traits help to ensure survival.
It may also be possible to plant corals with a range of different genetic traits, so that disease would not wipe out an entire population.
The Hong Kong restoration, if it continues to go to plan, could be implemented more broadly in the region and elsewhere.
On the Dongsha Atoll, part of a marine reserve administered by Taiwan but closer to Hong Kong, for instance, there are some 300 species of coral, far more than the 100 or so in Hong Kong. – DPA
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