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Friday, December 01, 2017,17:35
Desert in the depths
By Honey Tsang
Friday, December 01, 2017, 17:35 By Honey Tsang

Hong Kong is struggling to save its dying fisheries. The once bountiful are becoming barren, as the effects of global warming reveal themselves close to our shores, Honey Tsang reports.

On a clear morning, with the summer heat lingering into autumn, Ng Wai-keung sat bemused reflecting on days gone forever, when his family could make thousands of dollars a day harvesting sea urchins. They were so good they could be eaten raw. Today only a few remain and the fishery is almost gone.

“Back then, the sea urchin was a staple in Sai Kung waters. It’s a plump, scrumptious delicacy,” he said. Those days have passed and are not likely to return, thanks to human activity in and around the sea urchin habitat.

In the 1970s and 80s, Ng’s family could sell bucketfuls of sea urchin roe to Japan. Profits were so good, the family was comfortably well off. Later, by the late 1990s, overharvesting by licensed fishermen and illegal fishing by non-local vessels put the local sea urchin population in peril.

The daily harvest plummeted. Some days the harvest would amount to a few bowls worth only a few hundred dollars. It’s never come back.

Ng quit fishing at last, ending a family tradition spanning four generations. He was among many who turned their backs on the sea. 

SOURCE: ENVIRONMENTAL PROTECTION DEPARTMENT (EPD)

Hungry urchins

The native sea urchin, or Anthocidaris crassispina, deep purple in color, had always been battered by destructive plunder. But, a new threat, global warming — another pernicious influence barely noticed in the past — began to take its toll from the 1990s onward.

“We saw local sea temperatures rising and marine populations dropping,” Ng said. “We believed they were linked, but couldn’t wrap our minds around how one led to another.”

Kenneth Leung Mei-yee, professor of Biological Sciences at the University of Hong Kong (HKU), helped to make the connection. In 2015, he made the discovery that Sargassum siliquastrum (S. siliquastrum) — a brownish algae and the mainstay of the sea urchin diet — has been perishing all over the waters.

S. siliquastrum is the dominant species of seaweed found in Hong Kong waters. It is edible and used in Chinese medicine. It’s a perennial organism, flourishing and reproducing in winter and dying back in summer.

To scientists, Sargassum plays a vital role in the ocean. It creates a canopy, doubling as the undersea jungle, to give camouflage, shelter and food that feeds specialized marine creatures, from the bottom up along the food chain. 

The fact that S. siliquastrum is vanishing in both pristine, protected marine parks and heavily fished areas shocked Leung, as he undertook his decade-long research of the city’s marine ecology.

The warming sea temperatures in recent years, he observed, are making Hong Kong waters inhospitable to S. siliquastrum.

Among the 400 Sargassum species worldwide, S. siliquastrum is a temperate zone species. In times past it would flourish in cooler months from December to January, when the sea temperatures remained between 18 C and 20 C.

“Climate change is making the city’s coastal waters too hot for S. siliquastrum to procreate during winter,” said Leung. 

In 1986, the average sea temperature at Port Shelter waters, south of Sai Kung, was around 18.97 C in December, according to the Environmental Protection Department. Three decades later, in December 2016, it increased to 21.83 C, at a rate of about 0.95 C per decade.

Leung wasn’t the only ecologist who saw this coming. Ang Put, professor of  the Marine Science Laboratory at the Chinese University of Hong Kong (CUHK), who spent years studying Sargassum, was alarmed by the declining of S. siliquastrum

In recent years, Ang observed, the reproductive period of temperate Sargassum species, like Sargassum hemiphyllum, has been pushed back two months, from March to May. He deduced, the warming seas had upset the reproductive timing of temperate Sargassum species, which probably led to recent sharp decline of S. siliquastrum.

It’s a proposition widely shared among scientists that the marine creatures had been undermined by the delayed onset of winter, and the earlier arrival of summer than in the past — irrefutable signs of climate change.

Weather records tend to validate the assumption. Last year, a record-breaking 38 “very hot days” of 33 C or above were recorded, a 540 percent increase over 1986, when only seven days of extreme hot weather were recorded, according to the Hong Kong Observatory.

The number of “cold days” of 12 C or below also fell, from around 29 days between 1885 and 1914 to 16 days between 1987 and 2016.

“As a result, Sargassum has fewer cool days to germinate. Then the warmer weather of summer induces an early onset of the annual die off, largely upsetting its normal life cycle,” Ang explained.

However, there are many other factors at play in ocean waters, Ang stressed, and cited a research he conducted in 2007 in Tung Ping Chau Marine Park, where a bloom in the sea urchin population consumed the entire algal bed, leaving it barren. The explosion of sea urchin colonies was caused by the ban on commercial fishing in the park since its designation in 2001. It was a “well-intentioned” marine project, yet, one that led to unanticipated negative impacts, aside from climate change, on S. siliquastrum.

As for non-protected seas, land reclamation and man-made pollution might be other potential factors that have contributed to the decline of the algae, Ang added.

SOURCE: EPD

The bad spreads

Now, only a small quantity of Sargassum remains, scattered in Tung Ping Chau Marine Park and some non-protected waters in Sai Kung, where the sea temperatures are still cold enough for the algae to grow.

Professor Leung agrees warming seas are to blame. “The decline of Sargassum has reverberated along the marine food chain, with far-reaching implications,” he said.

With Sargassum depleted, its main predator, sea urchin, has turned to attacking the algae attached to coral reefs. Coral in Sai Kung, mostly the grooved Brain Platygyra Coral, has been ripped open by sea urchins questing for food.

“The feeding process can be very destructive,” said Leung. “It poses an added threat to the city’s coral, already bleaching out under global warming.”

Humans, at the top of that food chain, are now beginning to experience the effects. A fisherman who operates an aquatic farm near High Island at the southeast of Sai Kung suspects the dwindling S. siliquastrum, for one reason or another, is menacing the yields: “The sea urchin harvested these years was not as meaty as before,” he said.

The sea matters

Hong Kong harbors a wealth of marine organisms. Its 1,651 km2 marine area is home to around 6,000 marine species, amounting to 26 percent of all marine species recorded in the mainland, according to a 2016 study by HKU.

Hong Kong has more hard corals than the entire Caribbean Sea and more mangrove tree species than are found in East Africa.

Scientists credit the city’s geographical position, between temperate and tropical regions. Local waters are swept by the Kuroshio, Taiwan and Hainan ocean currents, making the city’s waters hospitable to both tropical and temperate species. But it’s also a situation that makes Hong Kong waters more susceptible to climate change, scientists agree.

Some marine creatures, unable to bear the warming temperatures, will be lost.

Ng Wai-keung (left), who ran a family fishing business during the 1970s-80s, and his wife Wong Sze-man recollect past times when the sea urchin industry waxed and waned. (EDMOND TANG / CHINA DAILY)

In the heated soup

Climate change is proving worse than early expectations. Carbon dioxide (CO2) from burning fossil fuels is also turning the sea more acidic, as CO2 absorbed in the waters is transformed into carbonic acid. 

An increase in seawater acidity impedes the growth of fish larvae, making them more likely to perish before reaching the adult stage.

Since the onset of the Industrial Revolution in 1760, ocean acidity has increased 30 percent owing to human activity. The average pH of the world’s oceans has fallen from pH 8.2 to 8.1 on a logarithmic scale — pH 7 is considered neutral, pH 1 highly acidic.

In Hong Kong, the annual average pH of Mirs Bay waters, a bay lying next to Sai Kung, from 1986 to 2016, fell from pH 8.2 to pH 7.9.

Acidification affects sea creatures composed of calcium carbonate like shellfish, echinoderms, calcifying coral and algae. The calcification of marine larvae is already happening. 

In 2015, acidified waters killed countless oyster larvae in the US Pacific Northwest. The loss costed the fishing industry nearly US$110 million and affected 3,200 workers. 

Global warning

Ng and his forefathers, dubbed the “boat dwellers”, lived on a junk, off Sai Kung. Back then, they paddled out to sea at 6 am, spending a long stretch hunting for sea urchins — the hard way, with a long rod with a hook at the end.

 “Locals didn’t venerate the gifts of the sea. They pillaged the waters as if it was up for grabs,” Ng said, with emotion.

 Two-thirds of the earth’s surface is covered by water that has become a “CO2 sink”, a garbage disposal for man-made emissions of carbon dioxide. The absorption of CO2 into the oceans, until now, has served as a brake to lessen the greenhouse effect. But the oceans’ capacity has limits, and their capacity to absorb more emissions will run out. When that day comes, it may be too late to save the planet from catastrophic change. 

Cooling down the threat

The HKSAR has advanced protective policies to prevent further deterioration of the marine environment. A prohibition on trawling in local waters was ordered in 2012. Five marine parks and one marine reserve have been designated since 1996, to safeguard habitats and marine species. 

We saw local sea temperatures rising and marine populations dropping. We believed they were linked, but couldn’t wrap our minds around how one led to another

Ng Wai-keung, former sea urchin harvester in the 1970s-80s in Sai Kung

Marine parks contain about 25 percent more fish species than non-protected areas in Hong Kong, according to last year’s study by Professor Kenneth Leung of HKU. Only indigenous fishermen are permitted to fish in marine parks, except Cape D’aguilar Marine Reserve where all fishing is banned. Creatures in marine parks grow unimpeded. Eventually, the parks will overflow and contribute to the restoration of local fisheries resources, Leung said.

Still, marine protected areas account for only 24.3 km2 — around 1.5 percent of Hong Kong’s total marine area. Scholars argue that these scattered protection zones offer little ecological protection.

Larger, highly mobile marine species like Chinese white dolphins, listed since 2010 on the Red List of Threatened Species (International Union for the Conservation of Nature), might obtain no benefit from the protected areas. 

Conservationists and marine scientists demand better mapping of protected areas and expansion of conservation to create a chain of protected areas.

Legislative Council member Ho Chun-yin, of the Agriculture and Fisheries functional constituency, acknowledged the decline in fisheries near our shorelines — moderate, so far, but accelerating.

In 2015, a massive red tide — an excessive multiplication of the algae Karenia mikimotoi — broke out in Tolo Harbour, Tai Po. The bloom consumed much of the oxygen in surrounding waters. More than 36 metric tons of marine life in nearby fish culture zones suffocated.

Professor Ang Put of CUHK suggested the best approach is to work on the root cause, the emission of CO2, by cutting greenhouse gases and relying more on clean, renewable wind and solar energy.

In 2017, Hong Kong set out its Climate Action Plan 2030+, pledging to reduce CO2 emissions by around 70 percent by 2030, compared to 2005 levels. 

Much can be achieved by scaling back coal power and increasing use of non-fossil fuel sources. From now until 2030, Hong Kong expects about 3 to 4 percent of its energy needs will be produced by renewable sources, wind and other forms such as solar energy and conversion of waste materials, according to the action plan.

Contact the writer at honeytsang@chinadailyhk.com


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