Read Time2 Minutes, 37 Seconds
By Amber Cobley

Photo Credit – Linda Sadlers (From Cornish Guardian

Moon Jellyfish – what are they?

Discovered whilst walking by Linda Sadler (photo credit), the species of jellyfish that washed up today is called the “moon jelly”, or their scientific name is Aurelia aurita. They are found in all UK coastal waters and are the most common jelly we have. However, they have only become very common in Cornish waters in the past 5 years.

Matt Slater of the Cornwall Wildlife Trust said: “There are millions of jellyfish in our waters at this time of year. When I’m out surfing, I keep hitting them with my board.”

They feed mostly on plankton, which are tiny microscopic plants (phytoplankton) and baby animals (zooplankton) that live in the oceans. Particularly when there have been large plankton “blooms”, you can get massive swarms of Moon Jellies which can change the colour of the ocean surface and even slow down boats!

So what may have caused this mass stranding of Aurelia aurita on Perranporth today?

Why so many?

First of all, we have to consider what may cause a jellyfish bloom.  If the jellies feed on plankton, then it is logical that numbers increase massively with a matched increase in plankton.  During the most recent half term, fisherman noted high levels of “glint” (plankton) in the water. Karl Fice-Thomson, beach school educator in Newquay notes “the water was literally milky-white with the blooms!”. There will be a “lag time” between the bloom of plankton and the bloom of jellies, because of course, the jellyfish need time to have their fill of the soupy water and reproduce into a large bloom.

What went wrong?

Scientific studies have shown a link between wind and stranding events of jellyfish. However, it is not as simple as “the faster the wind, the more jellies are washed ashore”.  There appears to be winds too weak to cause any drastic change in the jelly bloom migration, and then optimum wind speeds which cause them to wash ashore. However, above a certain level, because of the complex relationship between winds and wave formation, there appears to be some winds too strong. This all changes depending on where you are in the world and at what time, and on top of this, the wing direction can add further complexity on top of this! Unsurprisingly this is an area of science with lots of studies all over the world.

These jellyfish don’t offer a very harmful sting, although around the edges of the “umbrella” of the jelly, there are numerous hollow tentacles surrounded by hundreds of stinging cells (nematocysts). The best way to identify that it is in fact a Moon Jelly are the four purple-blue horseshoe shapes in the centre of the umbrella, which are actually the gonads of the animal.

There are a whole load of reasons why this stranding could have happened, and maybe we will never know… that’s real science for you!

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