Years ago, when I was new to marine biology, I booked a dive trip in the Galapagos Islands. Being a novice scuba diver, it took a while to get geared up for my first dive, and I was the last to jump off the boat. I descended, alone, with visions of hammerhead sharks, marine iguanas and other fantastic creatures that made these islands famous.
Instead, I saw something beyond my imagination. An open-ended cylinder about 2 feet long and 6 inches in diameter pulsed before me in the water column, flashing brilliant blue-white light. It was like swimming with an enchanted light fixture.
I had the good fortune to have crossed paths with a pyrosome.
Pyrosomes have been in the news this summer because masses of them are, for the first time, showing up along North America’s northwestern coast. No one knows why the strobing creatures have multiplied to such numbers, why they’re off the West Coast or whether we’ll ever see such a phenomenon again. Only the creatures know what’s happening, and they aren’t talking.
Ten species of pyrosomes pulse throughout the world’s oceans, each in the shape of a hollow tube. The difference between the species is size. The smallest grow only a few inches long. The ones off the West Coast are about 8 inches long and have the cute nickname of sea pickles.
There’s no canning jar, however, that could hold the biggest pyrosomes. They grow to 60 feet, as long as a six-story building is tall.
A pyrosome cylinder consists of thousands of tiny identical bodies, each held in position mouth-sides out, rear-ends in, by the tube’s mucus wall. Each clone sucks in outside water, eating its plankton and breathing its oxygen. The depleted water exits the rears inside, creating a current that propels the cylinder through the water.
Pyrosomes are famous for light flashes created by bacteria in each of the body’s two light organs. (“Pyro” is Greek for fire; “soma,” for body.) When a colony runs into a solid object or polluted water, individuals sparkle, a warning signal to neighbors, which pass it on. An alert results in waves of light that might frighten away a predator.
The following theory about pyrosomes has implications that should give us all stomachaches: Although impossible to prove, it’s possible that reports of a 1964 torpedo attack in the Gulf of Tonkin, which escalated U.S. involvement in Vietnam, may have been the flash of harmless pyrosomes. The creatures are common in that area.
During that Galapagos dive I had no idea what a pyrosome was, and, being separated from my guide and fellow divers, the encounter gave me a jolt of fear. Today the memory gives me a jolt of joy. I got to swim with a living, breathing crystal chandelier.
Reach Susan Scott at susanscott.net.
