The moon and the compass
[ places - april 02 ]
More jellyfish than usual visited us. While the sea isn't exactly jellyfish soup, it is certainly full of jellyfish croutons, softened by long immersion.
Jellyfish we are likely to encounter on Irish coasts are either 'pumpers' or 'drifters', which leave progress to the vagaries of the currents and winds.
In early July, I watched moon jellyfish, pumping to propel themselves, arrive on the tide into my local bay, and found many stranded on the beach when the tide retreated. The moon jellyfish is the one we see most. Bluish white, it is named for the four mauve 'half moons' on top of the transparent 'bell'. It can measure a foot across, but are mostly less than eight inches. Fine stinging tentacles and four frilly mouth tentacles hang beneath. Tiny fish are immobilised and slowly ingested The sting is too weak to be painful, even to children. Some fish fry have immunity - horse mackerel, haddock and others - and live amongst the tentacles, where they are safe from predators.
The compass jelly, the same size as moon jellys, also pumps itself along in swarms and is a familiar casualty on our beaches. Yellowish, it has dark brown lines radiating from the centre of the bell like a compass. It does not sting humans and, apart from feeding on small fish, leads a blameless life.
The dangerous lion's mane jellyfish is golden with hundreds of thin stingers beneath it, like the hairs of a lion's ruff. Not unlike the compass, it is much larger and has no dark 'compass' lines. If one finds a marmalade blob of, say, three feet across suspended in the water near one, it is best to retire to the beach. The lion's mane can inflict a very severe sting.
Its purple-blue, cousin, cyanea lamarki, just 12 inches across and not so vicious. Other jellys she may have met do not have 'popular' names, if that is word. There are the dangerous, warty, mushroom-like pelagia noctiluca which, as the name implies, lives on the surface and lights up at night, and the large (36 inches), harmless rhizotoma octopus, like a tall, domed, yellow-white bell with eight blue 'legs' descending from the centre.
Amongst the jellyfish 'drifters' are the Salee rovers, also known as by-the-wind-sailors. These are sometimes washed up in legions after south west gales. What is found on the sand is both intriguing and pretty. Readers are regularly mystified by what they describe as three-inch see-through plastic discs, found in their hundreds, each as regular as if it was stamped out by a machine and patterned with concentric rings, seen when they are held against the light. Components for toys washed overboard from a container ship was one guess, bases of plastic water bottles was another.
Salee rovers have a soft body, the 'plastic' disc and a bluish triangular sail bladder, thin as cling film. From the sail, they are named after the Algerian corsairs that roamed the European seaboards in the 17th century, boarding ships and taking slaves at Baltimore, Co Cork, and elsewhere. Usually, only the disc is left after they are tumbled in surf and scoured by sand. They are harmless to humans, the colony of which they are composed finding nutrients in plankton.
There are a few dangerous species in Irish waters but, happily, all are rare. The infamous Portuguese man-of-war, like the rovers, move with the vagaries of the wind and are not true jellyfish, which are self-propelled.
The English named the Portuguese man-of-war after enemy 17th century gunships, possibly because it was unfriendly and carried a sail. The sail is triangular, a bladder like a wind sock, filled with gas. The man-of-war is a colony of creatures, living in symbiosis, one killing the prey, one digesting it, one providing the gas-filled bladder with its shiny sail, like a cock's comb, on top. With it, the colony sails the wide oceans.
The man-of-war was the most feared peril-of-the-deep for Greek sponge divers. The tentacles are almost invisible and may be 20 feet long. They can cause severe injury, even paralysis, to a victim who becomes enmeshed. I have seen their thin gossamer lines, catching the underwater light, when snorkelling off the Canary Islands.
Dead or alive, whole or in parts, the man-of-war can still sting dangerously. Some years ago, a friend, wearing a diving mask, searched a rock pool on the Sheep's Head for a lost knife. Suddenly, he was stuck as if by a cattle prod. A yard long piece of man-of-war tentacle was responsible. The scar on his forehead took weeks to heal.
There is quite likely a correlation between temperature rises, nutrients in the water and jellyfish shoals. In Japan, they say the jellyfish always come in mid-August, when the water warms. On the other hand, many species live in the sub-Arctic Atlantic, where huge leatherback turtles from Mexico eat them by the bushel. Now we see them, now we don't. Ocean currents and winds gather or disperse them.