There are an estimated 13 million golden jellyfish (Mastiglas papua etpisoni) in Jellyfish Lake on the island of Palau in the Philippines, but their sting is too feeble to trouble humans. Golden jellyfish need sunshine to feed the symbiotic algae that live on their back so they spend each day swimming in a huge shoal following the sun. They were once a completely distinct species called Spotted jellyfish (Mastiglas papua) but when the lake became landlocked 12,000 years ago, they gradually lost their spots and sting. They no longer needed it - their only predator is the white sea anemone, which is anchored to the lake floor and prefers to live in the shade.
The Internet is like a giant jellyfish. You can't step on it. You can't go around it. You've got to get through it.
Jellyfish move hundreds of metres up and down the water column each day. We once thought this was achieved by jet propulsion alone – sucking in water and spraying it out behind them - but research recently revealed a more complex picture. As the 'bell' of the jellyfish contracts and relaxes, it naturally causes the water around it to move in a way that creates a vortex behind it. This vortex propels the jellyfish forward, accounting for 30% of its movement without it expending any extra energy.
This process means that jellyfish drag water with them as they swim. The jellyfish mix the cold water of the deep with the warm water of the surface, pulling nutrient-rich water up to nutrient-poor areas and oxygen-rich water down to oxygen-poor regions. This all helps to sustain life in the ocean.
They aren’t always benign, though. In 1982 an inch-long comb jelly from North America arrived in the Black Sea via the bilge water of a ship. Mnemiopsis leidyi feeds on plankton and had no natural local predator. In less than a decade the population had reached a biomass of one billion tons – 10 times the weight of all the fish that are caught in the world each year. Known locally as the ‘Monster’, Mnemiopsis ate the plankton that fed the fish, so fish stocks plummeted by 85% and vast blooms of oxygen-hungry toxic algae exploded. The cost to fishing and tourism combined was $5.6bn. Then in 1989 another carnivorous comb jelly arrived: Beroë ovate, which only eats Mnemiopsis. Once it ran out of Mnemiopsis to eat, its population stabilized and fish stocks have since recovered.
The sting of a jellyfish comes from specialised cells in the skin of its tentacles called cnidocytes - literally ‘nettle-jars’.
The Turritopsis dohrnii is a tiny Mediterranean jellyfish (only 1mm across) that can have as many second childhoods as it wants. After it becomes sexually mature and mates, the Turritopsis can revert back to being a juvenile; it does so using a process called transdifferentiation, whereby the cells transform from one type to another and so return to a youthful state. Theoretically, the animal could do this over and over again, thus rendering it immortal. In the laboratory, 100% of the jellyfish sampled regularly undergo this change, making it entirely possible that normal biological death does not occur in this species.
This process, the switching of cell roles, is usually seen in other animals only when parts of an organ regenerate. However, it appears to occur normally in the Turritopsis life cycle. The jellyfish turns itself into a bloblike cyst. This cyst then develops into a polyp colony - basically the first stage in a jellyfish's life. The jellyfish's cells are completely transformed in the process, with muscle cells becoming nerve cells or even sperm or eggs. In the natural world, many Turritopsis succumb to predation or disease, but it seems like if they were left to their own devices it would be remarkably easy for them not to die. The process has been observed in Hydras, which are simple freshwater animals, also only a few millimetres long. Biologists have found evidence that they don’t undergo ageing either – so they too could be biologically immortal.
It would be spiteful to put a jellyfish in a trifle.
An adult jellyfish is called a medusa.
The Irish name for jellyfish is smugairle róin which means 'seal's snot'.
The biomass of jellyfish makes up 40% of the total biomass of the ocean.