Dramatic Images of Shenzhen Red Tide

The Shanghaiist (Nov 26, 2014) reports that on Monday (24/11/2014), guests at the Dameisha Sheraton Resort in Shenzhen were witness to a red tide, as the sea water at the nearby beach turned a deep pink color, stretching for hundreds of meters. Dameisha is located in Mirs Bay just a few kilometres to the northeast of Hong Kong
According to the Shenzhen Marine Environment and Resources Monitoring Center, the red tide in this instance resulted from a non-toxic, algal bloom. However, despite center’s insistence that the bizarrely coloured water is harmless, a restriction on swimming and direct contact with the water has been advised.
This is not the first, and probably not the last, case of strangely colored water appearing in China.

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The red tide cause was identified as the non-toxic plankton species Karenia brevis (according to this article). Aerial photographs printed by the daily mail show the extent of the bloom. Only two problems: 1) Karenia brevis is native to the Gulf of Mexico, 2) it is toxic. In fact HK AFCD does not even list this species in its red tide database, which would be odd since it has been monitoring red tides in Hong Kong waters for over 20 years…
So once again a tabloid (the UK’s Daily Mail) has not done its research properly.

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The Environmental Hangover from Mid-Autumn Festival

No doubt millions of people in China and around the world have enjoyed mid-autumn festival by being outdoors , lighting lanterns and enjoying the sight of a bright full moon.

But sadly many people leave the beaches and country parks littered with plastic: drinks bottles, glow sticks, food containers, lanterns and other junk. Much of this no doubt ends up in the water – if not in the same night or the following day, then carried off by birds or lost from rubbish trucks and bags. Here is a few pictures of the aftermath in Discovery Bay. Fortunately the beach in DB is privately owned by Hong Kong Resorts and therefore cleaned regularly. Other beaches are not and rely on volunteers to combat the tide of plastic rubbish.

 

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It’s raining, it’s pouring, the divers are snoring

Hong Kong's waters as seen by NASA's MODIS instrument in October 2002
The eastern half is clearly more blue and oceanic, the western half more yellowy from the Pearl River Estuary’s influence
Credit: Jacques Descloitres Aqua MODIS Rapid Response Team NASA GSFC

With the rainy season now in full swing, it’s time to talk colors. Water color that is, and I don’t mean painting, I mean the color of the sea in HK.

It’s actually not the same everywhere, because if you live in Lantau Island on the western side, you are closer to the Pearl River Estuary which carries a lot of mud and silt down into the sea. That makes HK’s western waters murky and muddier, and because the Pearl River also carries a lot of minerals and nutrients down into the Sea, it makes for much better growing conditions for phytoplankton – microscopic algae that float around in the sea. That tends to turn the water color green or yellow, too.
But the eastern side of HK is a different story. Here the water is more oceanic and blue-green because there is no big source of mud and nutrients. Corals love warm, nutrient-poor and sunlit water, so you find them more on the eastern side of HK – basically as far away as they can get from the big rivers.
So what’s all this got to do with the rainy season? Well, a big tropical downpour washes soil, nutrients as well as all sorts of rubbish off the mountains and into the sea…anywhere, so river or no river, the water goes yellowy-green.

If you are a diver, this gives you two rules of thumb for visibility in HK waters:
– East is best, west is worst
– don’t bother diving after rain: the more rain, the longer you have to wait for decent visibility to return. For your typical typhoon I estimate at least 5 days.