Some coral communities in the waters off Sai Kung are dying at a faster rate than in previous years and in other areas, divers and green activists have warned.
And they say the chemicals in some sunscreens used by beach-goers and snorkellers could be contributing to the problem.
Coral bleaching was found at a site popular with divers off Sharp Island, Sai Kung, in June, during a survey by the Eco-Education and Resources Centre and Green Power.
They found an area of coral stretching about 100 square metres that had turned completely white – a sign the coral is dying.
The divers carrying out the survey said some of the coral had deteriorated quickly – and within the survey period of two weeks it was almost dead.
“It just happened within one or two weeks and the coral went from a brownish colour to completely white. We’ve never seen this before,” said Ken Ching Sze-ho, a diver from the centre.
Ching surveyed a 500 square metre area west of Sharp Island; his colleagues investigated the area south of there.
Coral bleaching is a worldwide phenomenon in which coral whitens as the algae zooxanthellae – that coexists with the coral, provides food and gives the coral its colour – disappears. Some say rising ocean temperatures are to blame for bleaching, but the exact causes and process are not fully known.
Bleaching affects many species of coral – even the hardy pavona decussate, which is common in Hong Kong waters.
The problem has also been found to a lesser extent in other waters off Sai Kung, including near Pak Lap Tsai, Ung Kong and Tai Shue Wan. The condition of coral in these places was found to be worse than in the northeastern part of Sai Kung, near Tap Mun and Crescent Island.
The divers did not see any butterfly fish, which feed on algae, near the affected coral.
It was unclear if bad weather in June had triggered the bleaching, Ching said.
“The sea in June was exceptionally turbid. But we don’t know if that had any impact on the algae being able to conduct photosynthesis,” he said.
Dr Cheng Luk-ki, the head of science and conservation at Green Power, said there was no evidence of any long-term worsening of the water quality in Port Shelter, the harbour south of the Sai Kung peninsula.
Cheng said government data show that levels of nitrate and ammonia, the two most common pollutants, have been stable there in recent years.
But he said figures from the Observatory showed that average temperatures in Sai Kung’s southeastern waters had risen by 0.46 degrees Celsius from the 1948-1962 period to 1971-2000.
Cheng said the temperature rise was in line with what was happening worldwide, and it was not clear what impact the warmer sea would have on coral.
Activists have also warned of the potential adverse impact on coral of a chemical found in certain sunscreens, citing recent research by scientists from the United States, Israel and Singapore published in the journal Ecotoxicologyearly this year.
According to the research paper, the scientists found that the chemical benzophenone-2, which is used in some sunscreens, could be deadly for coral – even in tiny amounts.
The activists urged anyone going in the water to use biodegradable sunscreens, or those made from titanium dioxide or zinc oxide, or to wear ultraviolet protective swimming costumes.
A spokeswoman for the Agriculture, Fisheries and Conservation Department said it could not confirm the report of coral bleaching near Sharp Island without the exact location details.
She admitted coral bleaching had been found south of Sharp Island, near Pak A, Crescent Island and Chek Chau during the annual reef check, which is currently under way.
“We will keep monitoring the situation closely and continue our efforts to publicise, educate and remind the public of the importance of coral conservation,” she said.
Photo caption: Coral in the waters off Sharp Island in Sai Kung has turned white – a sign that it is dying. Photo: Eco-Education and Resources Centre
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