Wednesday 17 November 2010

Lion's Mane Jellyfish

Image: Dan Hershman via flickr
The lion's mane jellyfish is a giant among jellyfish. In fact it's the giantest of all jellyfish yet known, even if 'giantest' isn't a word. They are found only in the northern hemisphere. Actually they're found only in the northern half of the northern hemisphere, right up into the freezing waters of the Arctic. They really, really like cold water.

Lion's mane jellyfish come in a wide variety of sizes depending on how far north they are. Those that approach the warmest waters they tolerate, around half way to the equator, are smaller and a pale orange colour. The wobbly jelly body, known as the bell, may be a mere 50 centimetres in diameter. Pff, whatever.

As we move north into colder waters, we find the lion's mane getting darker in colour and bigger in size. Eventually they become the monstrosities we really want to see (from a safe distance) - dark crimson with a bell up to 2.5 metres (8 feet) across and tentacles trailing 120 feet behind. That's really long by the way. Longer even than the blue whale, the biggest animal to have ever lived. I'm guessing this ridiculous size is more about getting enough food in colder seas, rather than the jellyfish having a stretch in the cold or something.

Food for this creature is anything from tiny animal plankton to small fish and other jellyfish. The lion's mane's (seems odd to write that) bell is arranged into 8 lobes each with 60 to 130 tentacles, adding up to lots and lots of tentacles. Naturally, they sting. Thankfully, they are not lethal to humans. Hundreds of 100 foot tentacles... I think we got lucky there. The Lion's Mane (and now I feel like going down the pub) also has a load of arms at the centre of the tentacles. They're much shorter and help with actually getting food into it's mouth. That could be quite a journey!

Interestingly, a whole host of little fish swim about with the lion's mane, escaping death by tentacle and using them for protection instead. They can even pluck out bits of food before it reaches the jellyfish's mouth. I don't know if the lion's mane jellyfish is capable of getting annoyed, but if it can, that would probably do it.

The lion's mane jellyfish has a supremely odd life cycle, but that's actually normal for jellyfish. Adults can reproduce sexually, with the female carrying fertilised eggs in her tentacles. She still keeps them when they hatch into larvae. Only when they are old enough will she place them onto a stone or some other surface and leave them. At this stage they are a bit like Sea Anemones, stuck to the floor and waving tentacles around to catch food. This then develops into not one baby jellyfish, but a whole load of them! It's a whole stack of tiny jellyfish that break off one by one and start their lives, swimming about, if indeed you can call it swimming.

So the adults reproduce sexually, and then their young go ahead and reproduce asexually. Only then can they start the important task of becoming absolutely huge.

Can you believe they only live for one year? Suddenly it's not so surprising that they seem so uninterested in getting anywhere, preferring to drift nowhere slowly. They've already lived a full life by the time they became a baby jellyfish!

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