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
3. DO NOT LITTER. TAKE ONLY PICTURES AND VIDEO, LEAVE NOTHING BEHIND.
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:
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 Lantau
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:
Here are some images of some pretty right red tide patches. But what on earth is it that makes the water go red like this and is it dangerous?
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.
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.
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 scintillanswhich 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 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!