It may look like a balloon, but this is no party animal
ANOTHER LIFE: RACHEL CARSON, the United States’ early begetter of the environmental movement, knew about much more than the ominous silencing of spring by the toxins of DDT.
Her own science was marine biology, and her great early trilogy of books on the ocean has been my frequent inspiration, offering a flow of learning lit up by a loving absorption in “the mystery and meaning of the sea”, nurtured by her research across the Atlantic from Co Mayo.
In The Edge of the Sea (1955) she described finding a stranded Portuguese man-of-war on a South Carolina beach and, having kept it respectfully overnight in a bucket of saltwater, waded into a chilly March sea to hurl it (and its deadly stinging tentacles) as far as she could into the waves.
What struck her was the man-of-war’s behaviour as it fought to leave the shallows, trying to use a difficult wind by adjusting the shape and position of the colony’s gas-filled sail, set diagonally across its base. There was, she said, “a strong illusion of sentience. This was no helpless bit of flotsam, but a living creature exerting every means at its disposal to control its fate”.
When, these days, this common creature of the Gulf Stream arrives near Irish shores, we may think of global warming and the steady northward shift of warm-water species – perhaps even of dire predictions about jellyfish taking over an ocean emptied of fish for human food. But occasional “invasions” of Physalia physalis around these islands have been recorded for a century or more. The last was in 2009, when more than 30 sightings along the east coast presaged much larger numbers out in the Irish Sea. The same may be true off the south coast this year. Swarms of anything up to 1,000 float in warmer tropical waters, and can be carried to these shores by a seasonal abundance of southwest winds in the great, warm river of the Gulf Stream.
The Portuguese man-of-war (originally named, apparently, for the resemblance of its float to the helmets of Portuguese soldiers) is technically not a single jellyfish but a siphonophore, an elongated, joined-up colony of individual organisms or zooids, each with a different function but working together as a team. Communication between them is maintained through a network of nerve fibres. None could lead an independent life.
The most visible zooid is the sail, or float, and its base. The oddly martial-looking sail is an iridescent party balloon, pink or blue or both, according to the light, and filled from a gland that pumps out nitrogen and carbon monoxide, with a moiety of argon, to stretch the balloon to perhaps 30cm.
While some siphonophores can deflate their float completely, sinking beneath the surface if the weather turns rough, the Physalia colony is limited to pumping it up or down to affect the speed of drift. How far it can “consciously” manipulate its voyage, as inferred by Rachel Carson, is part of marine biology’s continuing research into the animal’s mysteries.