Pretty in the water but nasty up close. This is Pelagia noctiluca or the mauve stinger jellyfish which grows up to 10 centimetres wide. It's also sometimes called the nightlight jellyfish because it produces a blue-green luminescent mucus.
Last year, a swarm of baby stingers, 26 square kilometres in area and 10 metres deep drifted into a salmon farm in the Irish sea and killed all 100,000 fish. The babies were small enough to be swept into the cages by the currents. This jellyfish is a Mediterranean species but has been seen along the British coast as far north as Shetland.
Scientists are putting this down to the warming of the winter sea water. Overfishing is killing off the natural enemies such as sunfish, trigger fish and loggerhead turtles that eat the jellyfish. And the jellyfish don't make shells so no carbon dioxide is absorbed from the ocean.
I've blogged about fish farms before and these jellyfish are part of a vicious circle. To feed people, fish farms are needed, fish farms are needed because of overfishing to feed people, overfishing means more jellyfish. To make things worse, small plankton-eating fish which compete with jellyfish and keep the numbers down are also being over-fished.......to make fishmeal to feed the fish in fish farms.