Jellyfish invade Petaluma Turning Basin

The pink jellies have returned to the Petaluma River.

After a hiatus of about five years, the Petaluma River is once again brimming with tiny “jellyfish” - not technically fish, however - to the surprise and delight of boaters, children, tourists and casual river watchers, many of whom were not around to see them back in 2012. That was the last time the mysterious, free-floating, non-native, soft-bodied, light-pink aquatic beasties appeared in such large numbers in the river.

Not that they actually went anywhere.

On the contrary, they’ve been here in the river all this time, in egg form, stuck to the river bottom, ever since their parents laid them during the last major Petaluma River jelly emergence.

“Adult jellies lay eggs, and then die, and their eggs basically go dormant, a cyst forming around them down in the sediment of the river,” explained biologist Cathleen Cannon, who first discovered and identified the local critters in 1993.

At the time, the city had a jelly-?naming contest, eventually dubbing them “The Pink Tzarina.”

“The eggs stay dormant for some time, for years, until conditions are right - the right salinity, the right temperature - and then they hatch,” Cannon said.

As Cannon determined in 1993, and has since been confirmed by other experts, the Petaluma River version are Black Sea Jellies, native to the Black Sea in Russia. They were probably introduced to San Francisco Bay waters by a visiting boat or submarine, expelling ballast water taken on in the Black Sea. Because the river is actually a tidal slough, connected through various waterways to the San Pablo Bay, the jellies eventually made their way to Petaluma on the tide.

“I’ve identified the same jellies in Napa, and in the Suisun slough,” Cannon said.

According to her, this current generation of jellies hatched around 10 to 14 days ago. People are noticing them now because they’ve finally become big enough, and exist in large enough numbers, to be noticed by the casual observer.

“I think of them as the great, great, great, grandchildren of the ones I discovered in 1993,” she said. “These are adults we’re seeing,” she added, estimating that the jellies’ lifespan can probably be counted in weeks, rather than months. “If people want to see the jellies, I suggest they go down to the river this weekend, because I don’t know if this generation will be with us too much longer.”

Cannon pointed out that, during years when the jellies hatch, they tend to do so in late June or early July. A lifelong educator, she has been encouraging parents take their children to the Turning Basin, to spend some quality time gazing into the water.

“Bring your phone and take video,” she said. “Just sit and watch, and after a while, you’ll see them. But leave them in the water. Jellies make terrible pets.”

Cannon suggested that the best time to see them is in the morning or the late afternoon, when the sun hits the water from an angle.

“You can see them pretty easily, all over the place out in the water,” reported Abigail Smyth, a rower with the North Bay Rowing Club, which has a riverside dock at the Petaluma Foundry Wharf. “Just standing on the dock, if you wait a few seconds, you’ll see one float up, hang out a second, then they sink back down,” she said. “They’re pretty small. Hey, maybe we should have a jellyfish eating contest.”

Asked if she thinks jellies are actually edible, Smyth laughed.

“Well, I’ve eaten jellyfish in other countries,” she said. “They’re rather chewy, as you can imagine.”

It should be stated - before any “peanut butter and jellyfish” jokes get taken seriously - that not all jellies are edible, and the particular species currently bobbing and breeding in the river should not be employed as snacks.

“All jellies sting, by the way,” Cannon said, in answer to the question of whether this species is dangerous. “Some jellies are very dangerous, though these do not appear to be. The Black Sea Jellies do not kill people that we know of. That said, anybody can have an allergic reaction.”

As to why they have suddenly hatched after such a long dormancy, Cannon says the answer to that question is not yet known.

“The question would be, how is the river sediment different this year, as compared to last year?” Cannon said. “What changed, and will these conditions be the same again next year, or the year after?”

(Contact David Templeton at david.templeton@arguscourier.com.)