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Discover the Secret Lives of Jellyfish

Nov, 26 2019

The underwater creature that flies like a bird but stings like a bee.

Despite not having a heart, blood, or a brain, jellyfish have been on earth for over half a billion years, outliving dinosaurs and surviving five mass extinction events. Some only a few millimetres long and some 500 lbs, today these creatures of all different shapes and sizes are still thriving, gently swaying in the currents. They have adapted to live in almost any ocean condition, from mesmerising bioluminescent deep-sea dwellers, to ice-loving Artic jellies, and the sun worshippers which live upside-down on the seafloor of tropical waters. Jellyfish have evolved unique abilities, which some would argue seem supernatural. Always beautiful but often dangerous, let’s dive into the mysterious lives of jellyfish and explore their squishy superpowers.

Almost completely made of water…

Believe it or not, some jellyfish are 98% water. The bell of a jellyfish – i.e. its main body —is comprised of two thin layers of cells with a watery material in the middle. This simple structure is an evolutionary trick which allows them to continue eating and growing without using lots of energy. Comb jellyfish are a harmless and abundant creature on our reefs at Coco Bodu Hithi and they are a major predator of plankton, voraciously consuming 10 times their weight every day in microscopic larvae and algae. 

With super speed…

The sting of a jellyfish is one of the fastest phenomena’s in the natural world. For such a simple creature, the process is a complicated piece of biological evolution. The specialised stinging cells which jellies use to paralyze their prey are called ‘nematocysts’; these contains a capsule with a little harpoon coiled up inside. Because jellyfish do not have a brain to control the stinging cells, the nematocysts are touch sensitive and triggered by the slightest brushing against any organic matter, including humans! Once activated, the stinging cells shoot the barb into the flesh of their victim at 10,000 times the force of gravity, one of the quickest mechanisms in all of the animal kingdom. Once the barb has struck its prey, a thin thread coated in a toxin erupts and delivers the poison.  

However, the stingers can only hurt you if the harpoon can penetrate your flesh, which is why some jellyfish are more dangerous than others. The box jellyfish can be lethal to humans, however sea anemones (a very close relative that has the same nematocysts), feel like sandpaper to touch – their stinging cells are firing but they are not strong enough to puncture your skin. 


The pièce de résistance is jellyfish’s ability to go back and live their youth a second time around. When ocean conditions are less than optimal, certain species (such as compass, barrel, and moon jellyfish) can reverse their development and revert back into jelly-children in order to wait out the unfavourable times. With the immortal jellyfish life cycle, they have truly unlocked the secret to eternal youth.  

Unlike more specialized creatures in the ocean, jellyfish can inhabit a wide range of ocean conditions. They can reproduce en masse when conditions are good, with large moon jellies witnessed releasing over 400,000 young at a time, and they are flexible enough to outlast other species when the environment changes. Jellyfish are the ultimate survivors and if their history is any indication, the bag of water without a brain may well outlive humans too.

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