MY SON MADE ME PROUD that day – by peeing on a little girl. Kitty, who he adored, was crying, and very little wrenches the heart like a child in real pain.
We had been teaching her to water-ski on a gorgeous, sunny morning, wading in the shallows, getting set up for the boat to pull her out of the water, and a large jellyfish swam into both her and me.
I’m supposed to be a grown-up, so sobbing with the truly horrible, burning stinging on
my chest, belly and legs would be extremely undignified, no matter how much I felt like it.
Poor Kitty was only five, however, had stings all down her leg and felt neither the need nor the ability to restrain her sobs.
We didn’t have any vinegar with us, and my boy, only four at the time, stepped up, unself-consciously, just wanting to try whatever it took to stop his beloved friend from hurting.
The old wives’ tale really works – the pee stopped the stings firing and somewhat neutralised the venom, and she stopped crying miraculously quickly.
Almost anyone who spends time swimming in our seas in summer is aware of jellyfishes, and they are almost universally agreed to be a negative presence. Even as a several-time sting “victim”, however, I find myself becoming more and more of a jelly enthusiast.
Every spring and summer, our seas are kissed by the Gulf Stream. They burst into life with the plankton blooms that feed the rich marine life around the UK. The basking sharks arrive at tide-lines to feed on billions of tiny copepods, and the fish stocks build up. It’s a lovely time, and we all head to the coast.
Every party attracts an unwelcome guest, and the stinging, gelatinous aliens seem to delight in coming into the sheltered bays in which we like to swim. They catch the unwary, and attack unprovoked.
Jellies have nothing vaguely resembling a brain – just a simple nerve net – so the idea of them deliberately going after a swimmer or diver is ludicrous. But whenever I’m in the water with them, I still get the unnerving feeling that they’re sneaking up on me.
Our negative associations with jellies don’t stop with their direct effect on swimmers or divers. It’s becoming widely accepted that pollution and overfishing increase jellyfish numbers – so we describe them as “fouling organisms”, and get to feel bad that our pollution probably helps these faceless, slimy stingers form huge aggregations, or blooms.
Whenever the media talks of over-fishing, and endlessly misquotes the same source that “80% of the fish will be gone by 2050”, they talk of how the jellies will take over the oceans.
Over-enrichment of water with fertiliser run-off and sewage reduces oxygen levels in the sea. Fish don’t do well with this, but jellies thrive.
The nutrient-enrichment probably gives a bit of a kick-start to their season by providing their prey with more food, too.
Overfishing simply removes many of the jellies’ competitors, allowing them to become more pre-eminent as consumers of small animals. In the super-productive seas off Namibia, a lack of patrolling has allowed overfishing to collapse large fish stocks, and jellies have expanded to fill their niches.
In 2007, a salmon farm in Scotland had its fish wiped out by a huge bloom of mauve stingers. These smallish jellies have a nasty sting, and also seem to like areas where small fish prey are concentrated, so compete with fishermen.
Periodic mauve stinger blooms have been tied to long-term fluctuations in fish stocks in the Mediterranean, going back over two centuries.
When it comes to whether pollution and/or climate change is causing an increase in jelly blooms, we have surprisingly little long-term data. But our suspicions are strong, and the evidence is building – our activities are almost certainly increasing jelly blooms.
Most jellies overwinter as tiny anemone-like polyps on the seafloor. The spring bloom signals the start of a new life-cycle, and they float off as small jellies to spend the next five months or so cruising in the plankton.
Unlike more complex animals, they don’t store fats for a future season, and they don’t have heavy musculature, skeletons or complex organs to build and maintain.
Their food just gets turned into an expanded watery body mass, and jellies and other gelatinous animals grow far faster than any other multi-cellular animal.
This is how, in a year with plenty of food, the lion’s mane jellyfish, native to the UK and the largest jelly in the world, can grow a bell that may be 2m across, and tentacles that may trail nearly 40m, in the space of a one-year lifespan.
Having no reserves makes it rather boom and bust, however. Jellies seem to keep growing until they run out of food, but once the spring and summer zooplankton supply starts to tail off, they weaken and die off.

LION’S MANES REALLY HURT, the worst of all the UK jellies. Strands from their mass of long, almost transparent tentacles have been left behind on many a diver’s glove, suit or mask, to give a nasty buzz when he or she is de-kitting. Sneaky buggers.
Even worse is on a dive, when an almost invisible tentacle drifts into that space between your mask and regulator, finding the one bit of exposed skin, and resulting in a sudden, unexpected, eye-watering sharp pain.
A full-on hit from a lion’s mane tentacle mass causes excruciating red welts on the skin, and enough of them could theoretically hospitalise you. The mysterious death in Arthur Conan Doyle’s story, finally solved by Sherlock himself, is, however, extremely unlikely.
I see more positives with jellies all the time. Whenever I visit aquaria, which have now learned how to keep jellies in captivity, I am invariably standing with a group of wide-eyed people, mesmerised by the strange beauty of the pulsating bell and the billowing tentacles.
It’s a simple beauty, delicate, not quite like the beauty of a flower, not quite like staring at an open fire.
The simplicity works, too. In the vast majority of the seas we never see, below the top 100m or so where copepods, krill, fishes and marine mammals rule, life is slower and more diffuse.
What works down there is a less energetic, less muscular, less concentrated life. Complex organs and dense bodies don’t work. In short, for most of the world’s seas, gelatinous animals rule.
Their boom-and-bust cycle and apparent increase may even be helping against climate change. The one biological phenomenon that sequesters carbon year after year is the sinking of faeces, moults and bodies to the seafloor. Gelatinous organisms like jellies eat until they’re clogged and fit to burst, but when they die, the sheer scale and numbers of them amount to hundreds of millions of tonnes of carbon a year falling to the seafloor.
Ecologically, jellies are both impressive and successful. We have a lot in the UK because we have particularly rich seas, of which jellies, like other predators, take advantage.
They may be watery, but their bodies are concentrations of the nutrients in their prey, and they are themselves exceedingly nutritious – basically packets of protein, vitamins and minerals hyper-expanded by water. Dried jellyfish is a delicacy in Japan.
Nature being nature, something has evolved to take advantage of this bounty, and we owe
to the jellyfishes the fact that the UK hosts the largest bony fish and the largest turtle on Earth each summer.
Leatherback turtles and ocean sunfish (Mola mola) are not only the biggest of their kind, but they are also fast-growing, thanks to jellyfishes.
They come to the UK every year, even though the waters are about as cold as they can stand, because there is so much gelatinous food here.
Because jellies are such a dilute food source, these predators have to eat huge amounts, then “condense down” the nutrients.
Leatherbacks can eat up to 200kg of jellies in a day, and molas in captivity have huge appetites and huge growth rates.
Molas chomp jellies with their broad, beak-like mouths, and leatherbacks catch them with their fang-like bony upper lip, then impale the jellies on backward-pointing throat spines.
To pack in the nutrients, the turtles then
pre-digest the jellyfish in their throats, belching out most of the water before passing the concentrated “protein shake” remains to the stomach, to be digested and absorbed properly.
Unfortunately for these rare giants, plastic bags look like jellies, and the same digestive system can be choked permanently by just a few such bags. Several million tonnes of plastic bags end up in the oceans each year, one major reason why the leatherback is virtually extinct in the Pacific, and in trouble in the Atlantic, despite abundant food supplies and improved protection for its Caribbean nesting beaches.
Some areas seem to be real hotspots for jellies – and thus for these giant jelly predators. The barrel jelly, which has a mild sting on its cauliflower arms and no tentacles, gathers in spectacular aggregations in a handful of bays off Wales, Cornwall and Ireland each summer, particularly in August.
Leatherbacks in particular seem to favour these satisfyingly chunky jellyfishes.

AS COOLWATER DIVERS with usually little skin showing, we’re safe from jellyfishes for the most part. Our major concern in heavily-jellied waters is stray tentacles on our gear when we take it off.
Like their relatives the corals and anemones, all jellyfish have stings – this is how they catch their food. Human skin, however, is somewhat thicker than the skin of jellyfish prey – the small and larval fish and crustaceans that ultimately make up most of the food in the oceans.
Our skin is too thick for many jellies to sting through, although cuts and grazes can weaken it enough for them to penetrate.
Jellyfish stings, or nematocysts, are microscopic, hydraulic darts loaded with a cocktail of toxins. These toxins are mainly neuromuscular, designed to paralyse their prey, which are far more powerful than the jellies.
Most of the lower surface of jellies below the dome and the tentacles is covered with millions of stings, though in most species this is only enough to provide a prickle or tingle to humans.
Urine works, as my son demonstrated, but drysuited adults are generally less inclined to either pee or be peed on – understandable, really. There’s probably a lawsuit in there somewhere.
So the tried and tested sachet of vinegar should be an essential part of your dive kit. Brushing off stray tentacles with a handful of wet sand is supposed to help get rid of tentacles without firing off more stings.
Avoidance is normally easy, however – jellies don’t lie in wait for us or sneak up on us, or indeed have any interest in us. They’re far too busy floating around, fishing.

JELLY, NOT FISH!
Jellyfishes are not fish, so “jellies” is probably a better name. They are one of several abundant and successful groups of soft-bodied, semi-transparent animals.
“Jellyfish” normally refers to the class Scyphozoa of the phylum Cnidaria, which includes anemones and corals. Slightly confusingly, another class of cnidarians, Hydrozoa, has many jellyfish-like members, but these tend to be smaller, and have different life-cycles and structures.
British waters have six commonly-seen species of large jellies. Five have many long tentacles around the rim of their bells, and four branched arms around the mouth underneath, marking them as members of order Semaeostomae.
The largest, and that with the most potent stings, is the orange-brown lion’s mane, Cyanea capillata, generally found to the northern edges of British seas. The smaller blue jellyfish, Cyanea lamarckii, is a close relative but with a much less dangerous sting.
The compass jelly, Chrysaora hysoscella and more potent mauve stinger, Pelagia noctiluca
are smaller, more slender-armed, elegant jellies.
Finally the moon jelly, Aurelia aurita, is almost transparent, with small oral arms, onspicuous
ring gonads inside the bell, and short tentacles.
The last British jelly is a different animal, a distant relative to the others and in another order, Rhizostomae. The barrel jelly, Rhizostoma octopus, forms large dense swarms and, unlike
the others, has no tentacles around the rim of the bell. Its eight large, bushy oral arms
form a cauliflower-like mass beneath it.

OTHER GELATINOUS ANIMALS
Other groups of animals have adopted a transparent or semi-transparent existence. Distantly related to jellyfishes are hydrozoans, simpler, usually smaller animals with complex life-cycles, including the bizarre Siphonophores, which are hyper-elastic colonies of stinging, feeding, structural and reproductive individuals.
Many hydrozoans have strong and varied toxins. The infamous Portuguese man o’war, Physalia physalis, is a simple siphonophore that occasionally reaches the UK in summer. Man o’war toxin and nematocysts seem to be unaffected by vinegar (or urine!), and are potentially very dangerous.
Other groups of gelatinous animals found around the UK are unrelated to jellyfishes
or indeed to each other, and have no stings. Ctenophores, or comb jellies, swim using parallel iridescent rows of swimming combs and catch prey with sticky tentacles, or by engulfing with their cavernous mouths.
Far more structurally complex are the salps, complex animals so closely related
to ourselves that we share a phylum, Chordata. In deep water, even familiar groups of animals such as octopus or squid tend to be gelatinous.