Red Tide Sighting at Mirs Bay and Tung Ping Chau Marine Park

AFCD Press Release

Red tide sighted
Friday, August 10, 2012A red tide was sighted in Hong Kong waters over the past week, an inter-departmental red tide working group reported today (August 10).

Staff of the Agriculture, Fisheries and Conservation Department (AFCD) sighted the red tide at Mirs Bay and Tung Ping Chau Marine Park on August 6. The red tide dissipated yesterday (August 9). No associated death of fish has been reported by mariculturists so far.

“The red tide was formed by Scrippsiella trochoidea, which is common in Hong Kong waters and non-toxic,” a spokesman for the working group said.

The AFCD urged mariculturists at Sha Tau Kok, Ap Chau, Kat O, O Pui Tong, Sai Lau Kong, Tap Mun, Kau Lau Wan and Sham Wan to monitor the situation closely.

Red tide is a natural phenomenon. The AFCD’s proactive phytoplankton monitoring programme will continue monitoring red tide occurrences to minimise the impact on the mariculture industry and the public.

Ends

For the original article click here.

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Red Tide Sighting at Tolo Harbour

AFCD Press Release 3rd August 2012

Red tide sighted
Friday, August 3, 2012 – A red tide was sighted in Hong Kong waters today (August 3), an inter-departmental red tide working group reported.Staff of the Leisure and Cultural Services Department and Agriculture, Fisheries and Conservation Department (AFCD) sighted the red tide at Tolo Harbour, including the Yim Tin Tsai and Yim Tin Tsai (East) Fish Culture Zones. It still persists. No associated death of fish has been reported by mariculturists so far.

“The red tide was formed by Scrippsiella trochoidea, which is common in Hong Kong waters and non-toxic,” a spokesman for the working group said.

The AFCD urged mariculturists at Yim Tin Tsai, Yim Tin Tsai (East), Yung Shue Au and Lo Fu Wat to monitor the situation closely.

Red tide is a natural phenomenon. The AFCD’s proactive phytoplankton monitoring programme will continue monitoring red tide occurrences to minimise the impact on the mariculture industry and the public.

Original AFCD Website Press Releas

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Stockings, Strainers and a jam jar – plankton fishing at Tai Long Wan

A group of Noctiluca scintillans
Source: Maria Antónia Sampayo, Instituto de Oceanografia, Faculdade Ciências da Universidade de Lisboa via Wikipedia.

The moon and stars shine dimly as the waves break on Tai Long Wan in Sai Kung on a hot summer evening, when the waves themselves light up with mini-fireworks as the waves crash on the damp sand. What is this magical display? Noctiluca scintillans (night-shining sparkling) also known as ‘Sea Sparkles’.
Sea Sparkles belong to a group of single-celled algae called dinoflagellates, that all share the same body plan: a single cell sometimes with armour plates, one long and one short hair, called flagella, that beat to move the cell along in the water or move water towards its mouth (technically a feeding groove). But Noctiluca scintillans is a bit special and here is why:

  • Its bioluminescent, that is it can make light using two chemicals stored separately in its cell, which cause light when mixed together. It’s just like a glow-stick where you bend the tube to crack an inner glass tube which releases a chemical into the rest of the tube and the two chemicals react producing light.
  • It’s not really an algae as it doesn’t photosynthesise. Instead of turning CO2 and H2O into sugars using solar-power, its more like an animal and eats other plankton both algae and animals.
  • It’s also into gardening. It likes to eat other algae, but instead of digesting them all it sometimes keeps them alive in little bubbles called vacuoles where they continue to photosynthesise. Imagine eating a potato and letting it just sit in a glass stomach to grow more potatoes and when it gets to full in your tummy, you digest a few spuds and leave the rest to grow more again….then you have the Noctiluca scintillans attitude to TV-dinners….can’t be bother to find new food all the time.

But whats all this got to do with stockings, strainers and jam jars?

Here is how I found Sea Sparkles using a home-made plankton net at Tai Long Wan (Sai Kung), and maybe you can, too:

Instructions for a make-shift plankton net
Ingredients: plastic spaghetti strainer, a pair of nylon stockings, some rubber bands and a few bits of string.
Directions: cut the strainer to leave only the circular opening as a frame for the net. Used one leg of the stocking and slip over the strainer frame and secure tightly with rubber bands. Attach string to three points on the frame and tie the ends together at  about 50cm length. Attach a rope to the knotted ends. Now cut a small hole in the foot end of the stocking and slip the stocking over a glass collection jar (clean jam jar, keep the lid for later), and secure tightly with rubber bands. Done!
Now tow it behind a kayak, dinghy or rowing boat for a couple of minutes, then gather up and remove the jar. All you need now is a magnifying glass or even better a microscope.

So when I looked at the plankton sample I gathered with this net under the microscope at home, I found Noctiluca scintillans, although it was pretty much dead at that point. It’s basically a super-thin bag jelly bag of air with two hairs coming off it. If you don’t have a microscope and are just using a magnifying glass, all you will see is round blobs up to 2mm in diameter. But if your sample is fresh and you are in a dark room or its night, give it a shake (close the lid first!) and maybe you will get some fireworks!

Two fatal cases of Vibrio vulnificus infection investigated

The Hong Kong government has given a press release about the deaths of two men from Vibrio vulnifcus on the 20th of June this year (2012) (press release).  V. vulnificus is a marine bacteria which can cause infection by ingestion (seafood) or through open wounds when swimming or wading in infected waters or via puncture wounds from the spines of fish such as tilapia. It prefers warm seawater or brackish (mixed fresh- and seawater) and occurs worldwide in warm salt-bearing waters and can be present in infected shellfish. It is a relative of the bacteria that causes cholera (Vibrio cholerae).

The infection presents itself with symptoms including vomiting, diarrhea, abdominal pain, and a blistering dermatitis. In people with compromised immune systems, V. vulnificus is eighty times more likely to spread into the blood stream, when it can cause severe symptoms including blistering skin lesions, septic shock, and even death . Severe infection may occur regardless of whether the infection began via contaminated food or via an open wound. There is no evidence for person-to-person transmission.

One of the two men was found to have consumed raw mantis shrimp in an investigation. I would stress though that there seems to be no reason to assume that we are more at risk in HK than anywhere else. Infections also occur in US coastal waters, Japanese coastal waters and anywhere where infected shellfish is consumed. Given that shellfish is cold-stored and flown around the world in todays world, infections can happen almost anywhere. If you are concerned, the press release issued the following safety guidelines for the public:

People are reminded to adopt the following measures to prevent necrotizing fasciitis and Vibrio vulnificus infection:

* Avoid exposure of open wounds or broken skin to seawater or salty water;
* Wounds should be thoroughly cleaned and properly covered;
* Wear thick rubber gloves when handling raw shellfish;
* Cook seafood, especially shellfish (e.g. oysters, clams, mussels) thoroughly; and
* For shellfish, boil until the shells open and avoid cross-contamination of ready-to-eat food with raw seafood.

Patients should seek medical advice promptly if they develop symptoms and signs of infection such as increasing redness, pain and swelling.

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.