Boneless, Brainless, Heartless Survivors

Just when you thought it was safe to get into the water, let us introduce you to the Aurelia aurita, commonly known as Moon jellyfish, a reference to its moon-like translucent bell.

For most people, jellyfish and the “ick-factor” go together, but to us, they are intriguing creatures. And you have to admit, these are rather eye-catching. You probably have seen these jellies, they are quite common in temperate and tropical coastal waters, harbours and estuaries. They float at the mercy of wind and current, and gather in quiet bays.  They vary in size – most of the ones we photographed were about 8 to 12 cm in diameter, but they can get as big as 40 cm!  They are very distinctive and quite beautiful with their translucent saucer and four bright pinkish horseshoe shapes in the centre, which, wait for it, are their gonads.

Moon Jellyfish-4The Moon jellyfish is capable of only limited motion and drifts with the current, even when swimming.   Instead of long trailing tentacles, the outer edges of the saucer are fringed by short, fine cilia, and four stocky arms in the centre of the bell, which all help bring food to the mouth.

The adult medusa as well as the larvae of the moon jelly have nematocysts, stinging cells to capture prey such as small plankton organisms, and also protect themselves from predators, although this does not seem to deter fish, turtles, birds and even other larger medusae from eating them!  These jellies pose little threat to humans as far as their sting goes as it does not penetrate well through skin.  Still, with the number that had accumulated around our hulls in the Gippsland Lakes, we were not keen on jumping into the water with them.

Aurelia aurita, moon jellyfishWhere aurelia become a serious threat though is when huge quantities gather, inexorably taken by strong currents. They have an uncanny knack for getting stuck in pipes, on nets, against screens. They clog intakes of power stations cooling systems and desalination plants, and can inflict deadly damage to aquaculture farms.

Scientists have also discovered that many sea jellies thrive in dirty, polluted and oxygen-poor water, so increasingly large infestations are yet another sign of a troubled ocean.

Moon jellyfish might be boneless, brainless and heartless, but they are survivors.  They have been around for at least 565 million years.  They have not needed to change their body form or their lifestyle in all that time, so they are doing something right… and lately they seem to be doing a lot more of it than normal!

With my new found interest in all things jellies, I was glad to find these images in my photo library, taken at the Gippsland Lakes over a year ago with the old Canon 60D.   Click on the first image to display in full screen slide show.

21 thoughts on “Boneless, Brainless, Heartless Survivors

  1. We paddleboarded though a huge patch of them in the Marlborough Sounds a couple of years ago. A weird sensation. I didn’t fancy falling off!

  2. I love watching the jellies float past the boat – they seem so graceful and peaceful. They do have the eek factor though for swimming.

    • They are very graceful … in small quantities. If you are interested look for another two posts on different jellyfish: ‘fire water’ (chrysaora wurlerra) and ‘Spaceships in the ocean’ (ctenophores). Even more spectacular!

      • They are spectacular!! I will be bum up and torch down next time I am near the prom 🙂

  3. here in southern New Jersey.. I have seen what happens when too many Jellies come ashore at once. It can actually get to the point where going into the surf is akin to getting stung. You don’t need to be anywhere near them when that happens, their stingers are free floating in the water.

      • I am unsure what we get here in NJ.. we get a couple of different types.. from small harmless all the way up to a Man-o-war that I saw washed up in Corson’s inlet when I was a child. The ones I am talking about are about 8 to 12 inches in diameter usually with a reddish or purple colouring towards the body centre.

  4. When I was a little girl my friends and I used to sneak up and drop jellyfish down each other’s tops – definitely the ‘ick’ factor at work here. We were never stung so I didn’t realize that they were famous for it until I was swimming in Cambodia and the water was full of ‘medusas’ as they called them there (French name for jellyfish?) Anyway, now I know. These ones are such ethereal creatures, quite beautiful in their own way…

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