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Thermal Extremes Threaten Hong Kong’s Tidal Zone

According to scientists around the world in July 2023 was the hottest month ever recorded on earth, while 2023 is on track to become the hottest year since records began.

Thermal Extremes Threaten Hong Kong’s Tidal Zone

As the planet now experiences frequent extreme weather events, this has meant longer, hotter summers in Hong Kong, with higher air conditioning bills to cope with overwhelming heat and humidity, and more time at the city’s beaches as residents try to cool off.

But the beaches are also feeling the heat. In particular, the intertidal zone where the land meets the sea and which is periodically uncovered by the fall of the tides. The rocky habitats that are exposed during low tide, and the marine organisms that live in this harsh environment, are also suffering from dramatic rises in temperature.

Professor Gray A. Williams, Director of the Swire Institute of Marine Science (SWIMS) and Professor in the School of Biological Sciences at The University of Hong Kong, said the rocks often heat up to over 50 degrees Celsius at low tide and the animals basically start cooking as they heat up and lose water.

“This puts a huge physiological stress on these organisms,” Professor Williams said. “And we're interested in how they can actually manage and cope with that thermal stress.”

Thermal Extremes Threaten Hong Kong’s Tidal Zone
Thermal Extremes Threaten Hong Kong’s Tidal Zone
Thermal Extremes Threaten Hong Kong’s Tidal Zone  

As part of an ongoing study into thermal stress on marine organisms, Professor Williams and his team are researching intertidal animals, including small snails called periwinkles, to see how they have adapted to deal with the temperatures on the intertidal rocks.

“The reason we chose to work on these species is because they are in this very extreme environment.,” he said. “And what we're seeing is that they're extremely well adapted to these very dry, hot conditions. And so it seems that these species are already able to cope with today’s very high temperatures. The question is what happens as we push them further?”

Dr Sarah Lau, a HKU researcher studying the physiological and behavioural adaptations of the periwinkles, believes they have evolved to stay alive by regulating their temperature using simple behaviours such as raising their bodies from the rock and standing on top of each other to form ‘snail towers’.

“They are basically reducing their contact with the hot rocks where they gain all the heat from,” Dr Lau said. “And then they're also exposing themselves to moving air currents so that they can be cooled down more effectively”.

Professor Williams said Hong Kong is ideal for this type of research due to its biodiversity, and because of its weather, geographic location and its unique marine environment.

“We have 25% of all the marine species known in China in an area which is 0.03% of Chinese waters, and that's quite remarkable,” he said. “And there are many reasons for that. There's our geographic location near the tropics and the influence of the Pearl River, for example, which gives us saline water to the east, freshwater to the west as well as our complex coastline; all of which create a rich series of habitats for marine organisms which we need to protect.”

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