Hong Kong's algal blooms - red alerts from nature
Environmental degradation is the most likely cause of a flood of colourful tides that washed up on Hong Kong's shores last month
The end of November saw areas of inshore waters across Hong Kong and east Shenzhen turn improbably colourful due to extensive red tides. Nighttime scenes were even more arresting, as seawater stirred by ferries flashed blue-green with luminescence.
The main phytoplankton in the blooms even turned out to be a bizarre microorganism.
It's scientifically fascinating but the red tides might be a sign that intense development in and around Hong Kong is increasingly unsustainable.
Red tides are formed by blooms of microscopic algae. They can occur naturally but they are often linked to pollution, such as phosphates from sewage and fertilisers. In the first six months, red tides were recorded on 35 days, reportedly the most since 1988.
A few red tide algae contain highly toxic chemicals. In 1998, one such species caused massive fish kills at fish farms. Otherwise, red tides are mostly harmless.
The Agriculture, Fisheries and Conservation Department said the main species causing November's red tides was Noctiluca scintillans. It's a dinoflagellate - a single-celled organism with two tiny whip-like structures, making it a feeble swimmer. Though unable to photosynthesise, N. scintillans can sometimes have a green algae cell inside, and form green blooms.
More typically, N. scintillans feeds on other microscopic life, and if these abound it can multiply to form tomato soup-like red tides.
This description fits the red tides I saw at Cheung Chau late last month. I also saw the bright, flashing bio-luminescence that has earned N. scintillans its sea sparkle name.
It's impressive to see the sea glow in the wake of a night ferry but the sparkling sea may reflect deep malaise.
Climate may have played a role in Hong Kong's recent red tides. Last month was unusually still and warm, and these conditions along with excessive pollution, likely resulted in the red tides.
While red tides have become commonplace in polluted western and central Hong Kong, it's unusual to have a large bloom in the east.
Indeed, as a red tide appeared at the Dameisha resort in eastern Shenzhen, some people wondered if the waters were red with blood from a shark attack, or if Judgment Day had arrived.
But Dameisha is right beside Yantian, a thriving new container port, with towering cranes and new tower blocks that have sprouted in the past decade. Pollution from here likely caused the red tides, which will become more frequent in the future.
Yantian is easily seen from still-tranquil northeast Hong Kong. If you visit Mai Po in the northwest, you see wall-to-wall developments that now throng the Shenzhen side of Mirs Bay. Close to Tai O, in the far west, work continues apace on the Hong Kong-Zhuhai-Macau Bridge.
Grandiose and mundane construction projects abound, as the Pearl River Delta continues to be transformed at a rapid pace. Nine cities are home to perhaps 60 million people and almost merge into a giant megalopolis, with no end in sight to the construction or the soaring population.
Hong Kong Chief Executive Leung Chun-ying seems unfazed, claiming it's possible to balance city construction and a healthy environment.
Though Leung surely did not see the red tides, he need only look out of the window to see the choking pollution that blights the region, or read reports to learn of freshwater shortages and severe heavy metal pollution of the delta's soil.
"Stretch a bow to the full, and you'll wish you had stopped in time," Taoist philosopher Lao Tzu warned long ago. Yet the rush continues, powered by greed and vainglorious notions, and with no time for ancient wisdom or common sense.
Scientifically, it's fascinating to witness and learn of the impacts of such growth. The recent red tides were astonishing, and it's intriguing to wonder about the effects of rising sea levels, particularly in a region historically prone to storm surges that could kill thousands.
But as a member of the most intelligent species we know of, it's infuriating and deeply troubling to be both witness to and a small player in this unfolding ecological disaster.
There's no comfort in knowing this is only part of a tragedy on a global scale. Doom is not inevitable. But the science is clear: we need to stop, rethink, change course, or we'll find that a "healthy environment" is just a fantasy, as our sea turns redder and the sky becomes murkier.
Martin Williams is a Hong Kong-based writer specialising in conservation and the environment, with a PhD in physical chemistry from Cambridge University