Tag Archives: red tides

Noctiluca scintillans Makes Global Headlines for HK

As reported by Apple Daily today, a recent bloom of the bioluminescent organism Noctiluca scintillans – often known as “Sea Sparkle” – and a frequent cause of red-tides in Hong Kong (recent posts here, here and here ), has occcured in the sea near Tai Po. The bloom has attracted more and more people hoping to capture the bioluminescence on camera. Some of the images and video have even made international media reports.

But the sudden influx of night-time visitors is causing some aggravation to villagers who are complaining about the noise nuisance. Many people have also been throwing rocks into the sea to agitate the single-celled organisms into sparkling, which is harming the local ecology.  While one or two stones thrown hardly make a difference, several hundred rocks hurled into the sea does create some damage. If you are reading this and planning to go and see the blooms, please DO NOT THROW STUFF IN THE SEA, NOT EVEN STONES. If you really want to see the sparkle then wade in to use your hands or a stick to agitate the water – but I don’t advise this either.


Some villagers have now taken to blocking beaches. Up to 100 visitors are coming to the beaches and cars are now blocking lanes causing a major disturbance to village life.


Advice on viewing Noctiluca scintillans in Hong Kong:

1. DO NOT THROW ANYTHING INTO THE SEA. If you want to agitate the bloom use a stick or branch to swirl the water. Or just watch out for waves which will do the same.

2. Respect local villagers. Do not be noisy and obnoxious. Do not block lanes


4.  Use a tripod and a slow shutter speed and high sensitivity (ISO) for long exposures to capture the full sparkle.5. If you can tame your urge to see the sea sparkle in person please do, it would really help the environment (and the villagers). You can just enjoy the images and videos floating around the internet,for example this (probably copied) video:

Click here to see irresponsible behaviour in the Apple Daily article ( so you know what not to do).

Noctiluca scintillans – Jekyll & Hyde of Plankton

This week red tides have been reported all across the western half of Hong Kong including Discovery Bay, Peng Chau, Mui Wo, East and West Lamma Channel. The culprit was once again the plankton species Noctiluca scintillans – neither fully plant not fully animal. It’s a single-called organism from a group called dinoflagellates. They consist of a bubble-shaped cell with two whips called flagella – that propel them through the water.


Though Noctiluca eats other plankton it doesn’t always kill what it eats: sometimes it leaves algae intact and stores it in little bubbles in its body (cell) where the algae make sugars that leak out and feed Noctiluca while the waste produced by Noctiluca feeds the photosynthesis of the preyed on algae – a process known to most as symbiosis and also found in tropical corals. However Noctiluca can also just eat the algae. Why and how it decides to eat or farm the algae is not really clear.
Noctiluca is a well known and non-toxic local red tide species and its occurrence is not necessarily a sign of pollution, but entirely natural. What is perhaps not natural is the size of the bloom, though. This could well point to agricultural fertiliser run-off and sewage effluent particularly from the fast growing population of the Pearl River Delta (PRD).

Images of the recent red tide at Discovery Bay North:

Noctiluca has however a redeeming feature – bioluminescence! That beautiful sea sparkle of iridescent blue that night divers in the tropics often sea or beach goers see in the breaking waves at night. So blood-red tides on the one side and beautiful sea sparkle on the other, Noctiluca is the Jekyll and Hyde of HK’s marine environment.

Long exposure image of a Noctiluca scintillans patch (cm via WikiCommons):


If you would like to know more about Actual toxic red tides in Hong Kong here is a little TV news documentary from 2013 I found on YouTube:

Red Tides, Fish Kills and iPhone Apps

Today I snapped a couple of images of some pretty right red tide patches in Discovery Bay. But what on earth is it that makes the water go red like this and is it dangerous?

red tide in DB
Floating patch of red tide in Discovery Bay 4/6/2014

Red tide is the collective name for phytoplankton blooms that tend to colour the water. Phytoplankton is made up of microscopic plants that drift through the sea. When conditions are right (mostly when there is nutrient-rich water and a stable water column) some species of these micro-algae form red tides. Depending on the pigments, the massive growth of algal cells may turn the water into pink, red, brown, reddish-brown, deep green or other colours.

"Pink" Red Tide on Tai Pak Beach
“Pink” Red Tide washing ashore on Tai Pak Beach in Discovery Bay 4/6/2014


Red tides are a relatively common sight in Hong Kong with 20-30 reports a year. The immediate reaction from most people is to think that they are the result of some terrible pollution. In fact the phytoplankton species are perfectly natural and normally occur in Hong Kong waters, but under certain conditions they can grow faster and form patches on the sea surface which we call ‘blooms’. Phytoplankton blooms by different species occur all over the world and are often seen by satellites with colour sensors.

Bloom of the phytoplankton species Emiliania huxleyi in the English Channel as seen from space by a satellite. The light blue comes from the seawater and the white calcium shell of the algal species.

Some red tides produce natural toxins, and can cause depletion of dissolved oxygen or other harmful effects, and are generally described as harmful algal blooms (HAB). The most conspicuous effects of these kinds of red tides are the deaths of marine and coastal species of fish, birds, marine mammals, and other organisms. This happens either as a direct effect of the toxins produced or because of oxygen depletion (known as hypoxia) which happens when the algae die and bacteria consume all the oxygen in decomposing the dead algae.
Only some species involved in red tides however are toxin-producing and cause fish kills. The bioluminescing species Noctiluca scintillans which I wrote about in an earlier post, is not toxic but still can cause red tides.
For Hong Kong this is an economic concern because of the many fish farms and aquaculture areas. When a toxic red tide drifts into a fish farming zone only early warning will help the farmers avoid large economic losses from fish kills by temporarily evacuating their fish cages or transferring their fish to tanks.
The Agriculture, Fisheries & Conservation Department (AFCD) of Hong Kong runs a red tide monitoring network which relies partly on fish farmers and members of the public.  The AFCD follows up reports by taking samples from the red tides and identifying the contributing species under the microscope to determine the risk to aquaculturists and the public. The majority of the reports are caused by non-toxic species. If you would like to know more about the network, the AFCD now has a fantatsitc  app for iPhone and Android (pictured below) with weekly updates and the functionality to report red tide sightings (which I proudly did today) with this new app, including submitting  pictures. (I would also recommend some of the other Hong Kong apps for marine enthusiasts out there:  HK Geopark, Wetland Park, Reef Check, Red Tide Information Network and the WWF Seafood Guide).


The AFCD’s “Red Tide” App for iPhone (also for Android). You can get weekly updates and also report red tide sightings. Available in Chinese (traditional and simpliefied) and English.


The AFCD started to record the occurrences of red tide since 1975. From 1975 to 2013, a total of 875 red tide incidents were recorded in Hong Kong waters. Amongst these incidents, only 27 were associated with fish kills.

77 algal species have formed red tides in Hong Kong, but majority of them are harmless. 19 of these species are considered harmful or toxic. Amongst these harmful/toxic algal species, only 5 of them caused fish kills and the other two caused contamination of shellfish by toxin in Hong Kong. The red tide associated fish kill events were mostly recorded in the 80’s and early 90’s.

So are there dangers to human health? If a red tide is identified as a harmful algal bloom (HAB) – then, yes, there is a risk:
The consumption of shellfish (e.g. mussels, clams) is one of the most common ways for algal toxins to impact human health. Each species has it’s own toxin so the health effects they cause are also varied. One example is Ciguatera fish poisoning. This type of fish poisoning is caused by eating fish that contain toxins produced by a the marine microalgae Gambierdiscus toxicus, which has been recorded in Hong Kong waters. Barracuda, black grouper,blackfin snapper, king mackerel, groupers and any large predatory fish can carryciguatoxins. People who haveciguatera may experience nausea, vomiting, and neurologic symptoms such as tingling fingers or toes. They also may find that cold things feel hot and hot things feel cold.Ciguatera has no cure. Symptoms usually go away in days or weeks but can last for years. People who haveciguateracan be treated for their symptoms. In Hong Kong with its rapacious appetite for seafood, ciguatera fish poisoning occurs quite frequently. For example, in 2004 it made up 7.9% of all food poisoning cases recorded that year. In June 2013, fourteen men and five women, aged 23 to 71, fell ill with ciguatera poisoning after eating coral reef fish at a restaurant in Sok Kwu Wan (Lamma Island). The fish in this case actually came from the Pratas/Dongsha Islands out in the South China Sea. Ciguatoxin’s is very stable, so cooking, drying or refrigerating fish will not destroy the poison. There is also no effective way to test fish for ciguatoxin, yet. If you want to play it safe avoid large predatory fish like tuna, grouper and others alltogether (they are mostly overfished already, especially blue-fin tuna, so you would be doing the planet a big favor).

So eating shellfish or fish which has been exposed to HABs is the main danger to humans. There are instances of skin irritations and breathing difficulties after direct human exposure to HABs but these are rarer and not as well understood. So to be absolutely safe, I would advise you to avoid contact with red tides – no swimming in, diving under or touching them!

Toxic Algae and Man-Sized Jellyfish

Once a swampy backwater of fewer than 20 million people, the Pearl River Delta—the southern swath of mainland China above Hong Kong—now has three times that population. Tens of millions more humans in the Pearl River Delta means many more toilets a-flush, pumping a steady gush of human waste into the South China Sea.
Read the full story at Quartz

SCMP: Mainland sewage fuelling Hong Kong’s ‘red tides’

According to the SCMP, sewage from the mainland is fuelling an increase of harmful algal blooms – known as red tides – in Hong Kong waters.

Professor Ho Kin-chung, dean of the Open University’s school of science and technology and an expert on algae, told the SCMP the red tides were “fed” by nutrients flowing in from mainland waters to the east and west of Hong Kong.

“The economic boom across the border leads to more sewage discharge into the sea and rivers, and in the right seasons [the nutrients] come down to us. So this is no longer a local phenomenon but a regional one,” Ho said.

Within the last fortnight brown algae been spotted across the territory – off Lamma Island, Cheung Chau, Lantau and within Victoria Harbour.

Agriculture, Fisheries and Conservation Department staff said they had spotted red tides at fish culture zones within Tolo Harbour, Sha Tau Kok and Tai Mei Tuk, while a member of the public reported another at Pak Sha Wan in Sai Kung.

Most algae absorb nutrients such as phosphates or nitrates that are commonly found in cities’ wastewater. At the right temperature, well-fed algae will proliferate in a short period of time.

Ho said Hong Kong was sandwiched by the Pearl River in the west and Mirs Bay in the east and these were the two key origins of red tides in local waters.

As a result, Tuen Mun, Lantau, Tolo Harbour and Sai Kung were becoming increasingly prone to the phenomenon.

Recent reports of large amounts of seaweed being washed onto beaches in South Lantau should not be confused with red tides. Red tides are composed of free-floating (planktonic) algae, seaweed however are larger marine plants normally growing attached to the seabed, reefs or rocks.

A spokeswoman for the Agriculture, Fisheries and Conservation Department said it would announce today whether tests had found the algae off Lamma Island to be toxic.

Four red tides were also spotted in Hong Kong waters last week.
Three red tides at fish culture zones within Tolo Harbour, Sha Tau Kok fish culture zone and Tai Mei Tuk were observed by staff members of the Agriculture, Fisheries and Conservation Department (AFCD) during April 8 to 10. Another red tide was spotted on April 9 by a member of the public at Pak Sha Wan, Sai Kung.

None of the red tides were associated with the death of fish in these occurrences.  “The red tides at fish culture zones within Tolo Harbour and Tai Mei Tuk were formed by Gonyaulax polygramma, Prorocentrum minimum and Heterosigma akashiwo. The one at Pak Sha Wan, Sai Kung, was formed by Gonyaulax polygramma whereas the one at Sha Tau Kok fish culture zone was formed by Heterosigma akashiwo and Prorocentrum minimum. All the above algal blooms are commonly found in Hong Kong waters. Gonyaulax polygramma and Heterosigma akashiwo are non-toxic. Studies have shown that Prorocentrum minimum may produce toxin, but no such reports or associated fish kills have been recorded in Hong Kong,” a spokesman for the working group said.

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

In 1998, a red tide killed 80 per cent of the stock at Hong Kong fish farms.

 Source: SCMP 17/04/2014 and AFCD Press Release 11/04/2014

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!