The night of the Jellyfish
The contrast of warm sun on my shoulders and cold, wet sand pressed firm against my feet working it’s way up between my toes was actually quite a pleasant feeling. It had been a long hot day at Arisaig on the Scottish west coast, and the fresher onshore breeze was a welcome break from the muggy heat that had surrounded us since the late morning. The tide was working its way back out to the Atlantic, exposing the strandline to the warm late evening sun – it’s near midsummer and this stretch of the highlands gets around 18hours of sunlight, even at midnight the night sky still has a glow about it. That means that my 10pm evening stroll was well lit, so it was easy for me to see everything that the tide had left behind; huge clumps of seaweed and remains of crabs littered the strandline picked apart by the gulls that noisily patrolled in search of a late-night snack. It wasn’t just the sound of the receding tide and the noisy seabirds I was being serenaded by this evening; the sand between my toes also appeared to be making noises of its own. It was like being stood next to a very large bowl of a well-known noisy cereal, as it snapped crackled and popped under my feet. Sand hoppers, hundreds of spring-loaded sand hoppers were working their way through the sand. There were so many of them that it looked like the beach was moving as they flung themselves about. It was these energetic amphipods that drew my attention to the glimmering orbs that lay in the sand amongst them.
Between the piles of bladder wrack were shining gelatinous discs, at first, I only noticed the one: a mound of wobbling goo that appeared to have the last remnants of the day’ sun trapped in its membrane. It glowed gold against the sand, just beyond the reach of the ebbing tide. More glints further down the shore caught my eye, strewn one after the other were huge numbers of stranded jellyfish, all left behind by the sea. I crouched down amidst the bounding sand hoppers and further inspected the ocean alien that led out in front of me, it’s shape flattened into the sand. In its centre were lilac coloured rings neatly nestled together. It was a moon jellyfish, and so were the other 20 plus bell shaped forms on the beach ahead of me.
I’ve never really given jellyfish much thought before, probably because I’d never come across them in the numbers that I have this year. They seem to be abundant on the west coast, and plenty of people I’ve spoken to (especially the sea kayakers) have reported seeing huge groups of them just off the shoreline. Swimming in the turquoise waters at Arisaig that afternoon, both Bill and I found ourselves dodging out of their way as they pulsed through the water alongside us. I was curious. Why were there so many at one time and how come there were such huge numbers ending up stranded?
What is a Jellyfish?
These gelatinous creatures are marine invertebrates. We recognise them most in their adult phase, which is known as the medusa phase, and this is when they are all bell shaped in the water with long dangly tentacles (worth noting that not all jellyfish have these long dangly tentacles). It’s these tentacles that release stinging cells into its prey…. or other things that aren’t its prey. The jellyfish’s reaction to touch stimuli is basically to throw some stingy cells at it because it doesn’t have a complex nerve system that can distinguish between things. Instead it has a nerve net that runs throughout its skin and allows it to detect movement – it just doesn’t know what’s moving. So, what about the jellyfish that don’t have long stingy things? Well, these are typically filter feeders feeding on plankton that they trap in mucus. In place of a stomach they have a “gastrovacular cavity” where the food is digested and with a diet that ranges from zooplankton to other jellyfish they aren’t overly fussy about what’s on the menu! People describe them as a simple life form and I suppose they are because they lack the complex nervous system and organs that other animals possess, but I think that makes them a pretty complicated little creature – there’s a lot going on under all that jelly.
Why so many?
The collective noun for a group of jellyfish is a smack, that’s a pretty satisfying collective noun if ever I heard one! But there is also a term that scientists use when a creature or plant appear in huge numbers unexpectedly, which could be applied to the large smacks of jellyfish that appear in our waters, and that term is a bloom. Blooms occur when the conditions are just right for the creature in question and that could be anything from the right weather conditions to an abundance of food/nutrients. It seems to be this summer that the conditions are spot on! Another factor to consider is the decline in the population of predators; dolphins, porpoise, turtles and other big fish eat jellyfish particularly when they are smaller and not fully developed. We all know these marine animals are facing their own battles at the moment and if their numbers are low then we are set to see an increase in jellyfish numbers. Meaning there a more and more smacks of jellyfish floating around the ocean.
What’s with all the strandings?
Ok, so this is the one I was really interested in; why are there so many smacks of jellyfish washed up on the beach in front of me? It’s a relatively easy explanation. Jellyfish move through the water by pulsating – they don’t have a lot of control about what direction they take or where they end up. This makes sense, I once watched a jellyfish being carried out into the Sound of Mull through the fast-flowing waters of Loch Aline. That delicate looking invertebrate had no choice, it had to go where the current was taking it and that’s the same for most other jellyfish, they literally have to go with the flow. Combine ocean currents with that seemingly pleasant onshore breeze I was talking about earlier and there is your recipe for stranding.
What Jellyfish do we get in the U.K.
I was quite impressed when looking into it the various types of jellyfish we get in U.K waters:
· Moon Jellyfish – sometimes called the common jellyfish because of it’s seeming abundance. Not a stinger due to its filter feeding styles but potentially could cause a rash.
· Lions Mane Jellyfish – this one stings! Mainly seen off the west coast of Scotland but if the winds blowing in the right direction then it could potentially end up on the North East.
· Blue Jellyfish – also a stinger but not as common.
· Barrel Jellyfish – if these don’t get eaten when they are in the small larval stage then they can grow pretty big, when fully grown they look like a jelly mould of a giant bottle stopper. These guys are usually found in the Irish Sea but also along the west coast. Apparently, they don’t sting but can cause a rash.
· Compass Jellyfish – these big marine jellies are usually found on their own and are uncommon in Scottish waters.
You can head here to find out more about the different jellyfish you can might find in U.K water, and if you do see any you might like to report it here at the Marine Conservation Society. Contributing your sightings to marine biologists can help to better understand this complex marine animal.
I’ve certainly had my eyes open to Scotland’s underwater world, without even having to get my feet wet (well, mildly damp if you count wet sand). I also think that looking into the life of the humble jellyfish has left me with more questions than I started with, but that isn’t necessarily a bad thing. However, I would much rather watch these jellyfish float through the clear water of the Scottish west coast than see them here like jellied pancakes in the sand though.
The next morning was cooler, a stronger onshore breeze was blowing creating rows of small waves that raced and foamed and the shore. There were no stranded orbs of summer sun that morning, they had all been washed back out to sea, reclaimed by the moving tides. But with that strong onshore breeze I was pretty sure that more moon jellyfish would be washed up on the shore, left by the sea as it exposed the strandline leaving it to the sand hoppers so they could make it snap, crackle and pop again.