Hong Kong’s coral communities have been found to be “generally in a healthy condition,” according to an annual survey organised by the Agriculture, Fisheries and Conservation Department (AFCD) and the Hong Kong Reef Check Foundation, despite some bleaching incidents likely caused by higher water temperatures.
More than 100 dive teams, consisting of over 1,150 volunteer divers, participated in the five-month review of 33 coral sites, which began in June. They recorded coral coverage, the health of the reefs, and indicator species – marine animals whose presence serves as a measure of environmental conditions.
“Coral bleaching was observed this summer at six survey sites, including Kai Kung Tau of Kat O, Au Yue Tsui of Yau Chau Tong, Wu Pai of Crescent Island, Coral Beach of Hoi Ha Wan and Siu Long Ke. The impact was minor and localised. It could be caused by the elevated water temperature in this summer,” an AFCP spokesperson said on Sunday.
Corals turn white when they are exposed to stressors, such as heat. While they can survive bleaching episodes, warmer waters linked to the climate crisis threaten the survival of coral reefs. According to a 2020 report from the United Nations Environment Programme, all of the world’s reefs will bleach by the end of the century unless carbon emissions are rapidly reduced.
Last year, record-breaking summer temperatures contributed to the biggest bleaching event recorded in years, exceeding notable bleaching seen in 1997 and 2017. A survey conducted last August by the AFCD, the Chinese University of Hong Kong (CUHK) and Hong Kong Baptist University found bleaching at 18 of 19 sites visited.
“Corals bleach during the hottest and coldest months in Hong Kong, but it’s usually minor, and they usually recover,” Apple Chui, a coral specialist and research assistant professor at CUHK, told a university publication last December.
“The massive bleaching events [in 2022] were due to unprecedented elevated seawater temperature. Fortunately, tagging and follow-up monitoring in October and November revealed progressive recovery of more than 96 per cent among the 102 corals tagged,” Chui added.
During the recent reef check, divers assessed the health of coral at 10 sites using the Coral Watch tool, a colour chart designed to measure how well reefs are doing, with deeper colours meaning healthier coral. The average health index of those sites was 4.28, slightly better than last year’s 4.06.
“The corals are generally in a healthy condition,” the AFCD said.
All 20 of the assigned indicator species were spotted during the survey, with butterfly fish, groupers, wrasses, snappers, sea cucumbers, sea urchins and cowries found in abundance. “A majority of the survey sites were found to have a high species diversity,” according to the AFCD.
The highest coral coverage was at A Ma Wan bay, off the small island of Tung Ping Chau in Hong Kong’s northeastern waters. Of the 84 species of reef-building corals found in Hong Kong, 65 grow around Tung Ping Chau.
Globally, Hong Kong waters make for a compelling study for marine scientists, as the turbidity, low salinity and cool winter water temperatures provide relatively harsh conditions. Corals that grow in Hong Kong waters are dubbed “super-coral.”
“Hong Kong is not an easy place for coral …The water quality has improved a lot over the last decade which had given us one important condition to keep the corals healthy. However, there are some external factors like red tides and typhoons which could take away our efforts in a blink of an eye,” Vriko Yu, a PhD student involved in a coral restoration project, told HKFP in 2020.
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