Honolulu Star-Advertiser © Susan Scott
September 19, 2011
In June a reader sent me a photo of a rarely seen creature she found in Hanauma Bay. A friend helped me identify the animal, about the size and shape of a Slinky toy, as a Portuguese man-of-war relative called a siphonophore.
That June 20 column prompted this email from photographer Wayne Levin: “I read your article with interest as it reminded me of something I saw off the south point of Honaunau Bay in South Kona a number of years ago. What I saw was 3-4 feet long and white. … I wonder if you may know what it is.”
Courtesy Wayne Levin
Pyrosome colony 3 to 4 feet long at the water?s surface off the Kona coast.
I did know what it was because Wayne included a good picture of the creature. The animal was a pyrosome.
Pyrosomes are a pain to explain because they live in the weird and wonderful world of offshore invertebrates. Few have common names, and unless you speak Latin the scientific names don’t paint much of a picture.
But a famous biologist’s 1849 journal entry conjures up an accurate image. T.H. Huxley, known as Darwin’s bulldog for his passionate defense of Darwin’s theory of evolution, wrote in his journal: “I have just watched the moon set in all her glory, and looked at those lesser moons, the beautiful Pyrosoma, shining like white hot cylinders in the water.”
Pyrosomes are tubelike — closed at one end, open at the other. They range in size from a half-inch to 100 feet long, and swim from the surface to 3,000 feet deep.
Each colony consists of tightly packed individuals embedded in a bumpy tube structure. The bodies’ mouths, directed toward the outside, suck in water, from which the animals extract food and oxygen. Used water exits into the pyrosome’s central cavity, resulting in a current that propels the colony up and down.
The individuals wedged in the walls of the colonies also contain a bit of magic: an organ that houses light-producing bacteria.
The pyrosome is one of the few animals that make light in response to light. When a pyrosome colony detects light, the leading individuals stop taking in water and turn on their lights, signaling the next bodies to do the same. Light sweeps down the halted cylinder in a wave. Such ripples of radiance might frighten or confuse predators, among them leatherback sea turtles.
Pyrosome light is no tiny twinkle. In a study on a research vessel off southwestern Oahu, researchers collected two pyrosome species and allowed them to adapt to the dark for an hour. When the scientists shined light on the creatures, one species glowed brilliantly (on average) for 11 seconds; the other, for 16 seconds.
This blazing light is where the creatures got the Latin name pyrosoma, meaning “fire body.”