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!

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