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).


Lion’s manes, invisible barnacles, suicidal fish, and photoshop hoaxes

It’s definitely summer and the sea has seasons, too. With summer comes the dread of Hong Kong’s beach-goers, the season of the lion’s mane jellyfish Cyanea nozakii.
This large, flat-topped jellyfish can grow to 50 cm in width with 8 bunches of 70 to 120 stinging tentacles that can trail up to 10 m. These tentacles can still sting even when they break off or are torn from the main body (though they lose potency over time).
It is cream to pale yellow with a darker centre and transparent on the outside edge.

A lion’s mane jellyfish (Cyanea nozakii) drifts close to the surface off Lantau Island.

You start to see these guys arrive from late March onwards and they reach their peak in mid-summer and decline in numbers after that.

Although it occurs all over the Indo-Pacific, seasonal outbreaks of the lion’s mane occur in the Yellow and East China seas and the Gulf of Bohai where fisherman regard them as a nuisance : first because they clog up nets and even damage them, second because their presence is linked to the decline of the edible jellyfish Rhopilema esculentum. Although it used to appear sporadically in those areas, it seems to have become more and more of a problem. One Chinese researcher even said that more harm and damage was caused to the coastal waters of China by this species than by red tides. Personally I have not noticed any change in Hong Kong over the years, but maybe I am wrong. When I was a kid (in the 80’s) I remember trying to count the number of jellyfish we passed off Lamma Island in our boat and lost count after 100 in 5 minutes…on average adults weigh about 1.2-1.3 kg so we passed literally a tonne of jellyfish in 5 minutes (and it was a slow boat).
So what about the barnacle and the suicidal fish?
Well, remember symbiosis from high school biology? The jellyfish are sometimes accompanies by other creatures taking advantage of the bad-ass protection offered by the stinging tentacles. One interesting guy is a transparent, soft barnacle called Alepas pacifica that hitches a ride by attaching itself to the outer rim of the jelly’s bell with a stalk and spends the rest of its life in care free existence filter feeding particles out of the water – not a care in the world. Until the jellyfish dies, then it will, too.

Three Jellyfish Barnacles (Alepas pacifica) attached to a jellyfish.

And the other two creatures are two commercial fish: the Razorbelly Scad (Alepes kleinii) and the Malabar Trevally (Caranx malabaricus). Both fish as juveniles like to seek out a lion’s mane soon after they hatch from eggs which – with perfect timing – seems to coincide with the arrival of the jellyfish. Hanging around the jellyfish gives them protection from predators. Think this is perfect adaptation? You would be wrong. The fish might gain an advantage from hiding by the jellyfish but they have not evolved any mechanism to avoid or deal with the stinging tentacles! Think of a child hiding from the bogeyman on top of a high voltage electricity pylon and you get a good idea of the risk to the fish. They have to swim very, very carefully! And on top of all that they are very loyal or attached to this dangerous fortress, too. When a jellyfish are caught and handled the fish stay with the jellyfish until inevitably they are forced into contact with the tentacles and are repeatedly stung until the die. Suicidal fish.

You can find more information on Hong Kong marine symbiosis in the book “Partnerships in the Sea: Hong Kong’s Marine Symbiosis” by Brian Morton.

An adult razorbelly scad (Alepes kleinii).
An adult Malabar Trevally (Caranx malabaricus). As juveniles they use the lion’s mane for protection from predators.

And now – sex:

Jellyfish can reproduce sexually and asexually. And when they chose sex it’s between male and female jellyfish – not that you can tell the difference unless you have a microscope and a lot of time. But like most invertebrates they simply try to time their spontaneous ejection of sperm and eggs into the water and hope that some meet, fertilise and grow into larvae. The microscopic larvae, called planula, are tiny, hairy, slipper-shaped things that use their tiny hairs (called cilia) to propel themselves. The planula larvae  of the lion’s mane only last a day and a half before they settle on the seabed and turn into small polyps like coral except solitary instead of in big colonies. After that they bud off little 2-3 mm wide jellyfish which then grow into the adult 20-30 cm wide jellyfish we all fear coming into contact with while swimming.

The life cycle of a jellyfish. Staring from planula larvae (1) to adult medusa (14). (From Schleiden M. J. "Die Entwicklung der Meduse". In: "Das Meer", A. Sacco Nachf., Berlin, 1869.)
The life cycle of a jellyfish. Staring from planula larvae (1) to adult medusa (14). (From Schleiden M. J. “Die Entwicklung der Meduse”. In: “Das Meer”, A. Sacco Nachf., Berlin, 1869.)

Photoshop hoax:

Some time ago the below image circulated online of a gigantic lions mane jellyfish dwarfing a diver.  This is actually a different species (Cyanea capillata) to our lions mane (Cyanea nozakii) even though it shares the same common name. Thanks to Google’s reverse image search the image was quickly exposed as a photoshopped fake as you can read in this Forbes article .

Photoshoped image of a lions mane jellyfish with a diver. L=Impressive sight, sadly a fake.
Photoshoped image of a lion’s mane jellyfish with a diver. L=Impressive sight, sadly a fake.
And finally some interesting recent research on the lion’s mane jellyfish:

– Researchers in Qingdao investigating the venom of the stinging tentacles found it was most stable for storage at -80 degrees Celsius and that it was more effective at killing human colon cancer cells compared with human liver cancer cells.

– Researchers in Lianyungang attempting to find some sort of use for the enormous unwanted by catch of lions manes in fisheries found that it is a good source of collagen and that compared to other sources of collagen it had lower levels of arsenic, mercury and lead.

– Researchers in Japan have tried to isolate the gene responsible for the lions manes production of an enzyme called endoglycoceramidase which is useful in synthesising some other molecules. Also in Japan researchers worked on the acoustic signature of different jellyfish species to develop an avoidance system for fishing boats. The acoustic signature is essentially the characteristics of the echo received from a pinger when the sound waves hit the jellyfish. Unfortunately they were not able to tell jellyfish species apart , which would have been a wonderful way to quickly measure their populations by just towing a pinger over a vast area and then estimating the population from the echo data.

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

Beach Blobs

Recently a reader sent me some pictures of yellowy-green blobs at Pui O beach and asked me if I knew what they could be. Beach blobs turn up on beaches all over the world and are actually a pretty interesting topic. Type ‘beach blob’ into a google image search and you will find a range of blobs from tiny and inconspicuous to giant and downright frightening blobs.


Blobs can be or be produced by any number of organisms including the egg cases of marine polychaete worms, dead jellyfish and any number of other partly decomposing marine animals.

After I looked at the pictures closely it seemed to me these particular blobs are most likely the remains of small jellyfish. The tentacles have either already decomposed and broken off or we’re very tiny to begin with. Only the “bell” is left.  The bell of the jellyfish is made of two firm layers of skin-like tissue sandwiching a layer of connective tissue called mesoglea. 

This mesoglea is a translucent, non-living, jelly-like substance  and is mostly water. Other than water, it contains several other substances including fibrous proteins like collagen. The mesoglea also contains muscle bundles and nerve fibres. It acts like an internal skeleton, supporting the bell and its elastic properties help restore the shape after it is deformed by the contraction of muscles when the jellyfish swims. If you have ever watched a jellyfish swim you’ll know it moves by opening and flattening the bell to draw water in, followed by contracting and closing of the bell to expel the water.
When I zoomed in on the pictures I could just make out 4 faint circular structures arranged in a cross in the middle of some of the blobs. These I am pretty sure are the gonads or sex organs of the jellyfish.

Anatomy of a jellyfish

The gonads are the cross-shaped circle-like structure in the center of this jellyfish.
The gonads are the cross-shaped circle-like structure in the center of this jellyfish.

Look very very closely and you may be able to spot 4 tiny circle outlines inside some of the yellow-green blobs. These are the gonads or sex organs of the jellyfish.

Unfortunately without the actual blobs in my hand or under a microscope I can’t say anymore than that. Jellyfish come in all sorts of sizes from microscopic to more than 2 m across so these could be juveniles or they could be adults.

Thanks to my reader for sending me this fun little mystery. If anyone else out there has any mystery pics that need identifying, please leave a comment and I’ll get in touch.

Global Citizen Science – Introducing the Secchi App

Screenshots of the Secchi App
Screenshots of the Secchi App

SecchiApp2Calling all budding marine biologists!
The University of Plymouth has developed an app that let’s you directly contribute to science by recording phytoplankton densities with the aid of a simple device called a Secchi disk – which you can make at home – and their free iPhone or Android app.
Phytoplankton are tiny floating algae that soak up carbon dioxide and nutrients and use sunlight to convert them into carbohydrates, proteins and fats to grow and release oxygen at the same time. Phytoplankton is very important for climate change because when they die they settle down to the sea bed either directly or by being eaten and then pooped out by animals. This process of binding carbon dioxide from the ocean and burying it layer upon layer of sediment on the ocean floor is often called a carbon sink.
Quite apart from this phytoplankton is also the basis of the marine food chain, so almost all other ocean creatures depend on it.
But many researchers have claimed to find a decrease in phytoplankton levels. But now you can help in what may become the worlds biggest phytoplankton study and help find out what is really happening with phytoplankton worldwide.
The app shoes you how to make a simple device called a Secchi disk – basically a flat circular disk lowers into the water by a rope. You then lower thie disk down into the water until it just disappears from view and record this depth – this is the ‘Secchi depth’. So basically you are measuring underwater visability in the vertical dimension.

how a secchi disk works
The Secchi disk measures the visibility of the water column in the vertical plane and this measurement serves as a crude measure of plankton density.

This is a so-called proxy for phytoplankton density in the water – it’s not the actual measurement of phytoplankton density but a measurement that is very strongly correlated to it, because phytoplankton is the main cause of visibility levels. So by measuring the visibility we can indirectly infer how dense the phytoplankton is in the water.
The app has full instructions on how to make a Secchi disk and how to make the measurements. So if you have access to a boat, download the app, and get busy as doing some ‘citizen marine biology’!

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!