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A massive patch or “blob” of warm water experienced along the usually cool U.S. Pacific coast from 2013 to 2016 wreaked havoc on the marine ecosystem. Fishermen in Alaska reported seeing warm water sharks, while California beachgoers encountered tropical poisonous water snakes. Though the return of cooler temperatures in 2017 rid the area of most unwanted visitors, bioluminescent pyrosomes (Pyrosoma atlanticum) have decided to stay and are now washing up along the coast in unprecedented numbers.
Though they look like a single organism, pyrosomes are colonies of hundreds, and sometimes thousands, of individual creatures called zooids that are enclosed in a gelatinous thimble-shaped tube-like covering which is open at one end. Also known as sea pickles, the pelagic creatures that are usually found in warm tropical waters are filter feeders. That means they eat plankton by filtering plankton-rich water in, and then expelling it through, the hollow interior of the colony. The efficient creatures also use this mechanism to move. According to biologist David Benett, "The combined force of the water from each zooid being ejected into this cavity and so out of the colony's rear thus propels it (pyrosome) along.”
The zooids possess light producing organs that illuminate in unison, emitting a stunning blue-green color that can be seen over 100 feet away. Often times, light from one colony causes other pyrosomes to glow as well, leading researchers to suspect that the organisms use the light signals to communicate.
Fascinating as they are, the pyrosome invasion on the U.S. Pacific coast is causing much anguish. The creatures are not only clogging waterways and fishing gear but also hindering scientific experiments. In May, researchers in search of a rare fish in the Columbia River gathered over 60,000 pyrosomes in their nets within five minutes. Long line fishermen trying to catch salmon and halibut are instead finding the organisms on every hook. Some scientists are concerned that pyrosome carcasses might deplete the waters of oxygen and create “dead zones” for other sea life.
Researchers are scrambling to find out why the creatures are appearing in such large numbers. However, given that in the past, pyrosomes have been extremely rare, there has been relatively little research done on these large colonies, which can grow between up to 60 feet long. While the creatures have numerous natural predators including dolphins, whales, and certain species of fish it would require large numbers to make an impact on the pyrosome population, that now stretches from northern California to the Alaskan coast.
“For something that’s never really been here before, the densities are just mind-boggling,” said Laurie Weitkamp, a Northwest Fisheries Science Center biologist. “We’re just scratching our heads.” Hopefully, scientists will be able to resolve the issue soon or even better, the jelly-like creatures will return to their warm habitat voluntarily.