Southern California waters see an invasion of pyrosomes

Southern California waters are experiencing an invasion of sorts by a strange sea creature called a pyrosome, and they're making headlines up and down the coast. 

Imagine a tube-shaped jelly about the size of a thumb that glows in the dark — leading to its name "fire bodies."

They're typically found in tropical waters, but scientists with the National Oceanic and Atmospheric Administration recently came across a huge population of pyrosomes off Southern California.

Their nets captured more than 93,000 -- the biggest local catch ever.

Keith Sakuma,  chief scientist on NOAA's team that caught the pyrosomes, told KPCC that their fast-growing populations are stumping researchers. 

"From [19]83 all the way up to 2011, pyrosomes were pretty much a rare catch," he said.

But since that time, he said, "they've never really left California" - and no one's sure why. 

What is a pyrosome? 

A pyrosome is made up of a bundle of organisms - each one so closely packed together that it resembles a single creature, Sakuma explained.  They produce their own light through bioluminescence. 

"People will mistake them for sponges or jellyfish, but they're not - they're really far away from these categories," Sakuma said. 

Pyrosomes are mostly spied in tropical waters like the Mediterranean Sea or near Australia - another reason why their rising numbers off the West Coast are so surprising to scientists. 

"It's kind of a mystery what's going on with the pyrosomes," Sakuma said. 

NorCal vs. SoCal

Pyrosomes have seen large numbers in California for a few years. Take a boat out in areas around Cape Mendocino in Northern California and south of Point Conception, and you'll probably see more than a few hotspots for pyrosome activity. 

But this year, Sakuma says catches off the coast of Southern California were much bigger compared to Central and Northern California. 

The area between Cape Mendocino and Point Conception only saw 45,000 pyrosomes caught - compared to 93,000 further south. 

Sakuma's team also found a difference in size. The average pyrosome between Cape Mendocino and Point Conception was over 100 mm long - but south of Point Conception, the size dropped to 22 mm. 

It's not clear why this is happening, Sakuma said. Warmer ocean temperatures in Southern California could contribute to the increase in pyrosomes - but temperatures have fluctuated over the years. 

"The ocean conditions in 2012 and since then have been very different year-to-year, and yet the pyrosomes are still there," Sakuma said. 

"It's a very strange ecosystem - a non-normal ecosystem."

Potential consequences 

Right now, pyrosomes are mostly just ocean pests weighing down fishing nets. But Sakuma says they can filter ocean water very efficiently, scooping up and feeding on large bundles of organisms like phytoplankton.

This could starve off important food groups like anchovies and krill - hurting bigger marine animals.

"The things that eat anchovies, the things that eat krill, like salmon, whales, they’re not going to switch and eat pyrosomes," Sakuma said, noting that in the future these animals might leave familiar coastlines in search of food. 

But while pyrosomes reproduce quickly, Sakuma says they also probably don't live very long.

"It really remains to be seen how big of an impact this is going to have," he said.