Ocean Sciences News

Why Trillions of Jellyfish Washed Ashore from Canada to California

Although warming oceans may make population booms and mass strandings more common, the species may ultimately be one of the beneficiaries of climate change.

By

During some years in the spring, so many jellyfish wash ashore on the beaches of Washington, Oregon, and California that they carpet the sand in thick, gooey mats. The jellyfish Velella velella can pile so high that taken together, they likely equal six and half blue whales’ worth of stuff.

Researchers now want to know where the jellyfish came from and what they could mean for the ecosystem.

“The question is, Are all those gazillions of Velella colonies out there eating all the fish eggs?” said Julia Parrish, a marine ecologist at the University of Washington.

New research from Parrish and her colleagues suggests that mass strandings of V. velella come from spikes in population caused by warmer-than-average ocean temperatures off the U.S. West Coast. The spikes have happened in 14 of the past 20 years.

“When we see gazillions of the Velella showing up year after year, they in fact are telling us that the system is breaking,” said Parrish. Climate change is expected to warm ocean waters, so V. velella strandings could become more common.

Although Velella can’t harm humans, the species is related to the venomous Portuguese man-of-war. Understanding how and why so many V. velella end up marooned on beaches could help scientists predict the movement of their more dangerous relative.

Run Aground

V. velella go by many names: by-the-wind sailor, purple sail, little sail, and sea raft.

A gelatinous mat of V. velella in Oregon
A volunteer sticks a ruler through a gelatinous mat of V. velella in Oregon. Warmer winter waters brought millions of these hydrozoans to the shore during an ocean heat wave called “the Blob” from 2014 to 2019. Credit: COASST

The hydrozoan, not a true jelly, spends most of its days floating on the surface of the ocean. It is approximately the size and shape of a potato chip, has sapphire coloring, and uses little tentacles on its underside to feed. Its most distinctive characteristic is a translucent fin that extends upward like a sail.

Scientists don’t know how far V. velella travel, but when groups are in the wrong place at the wrong time, the wind blows them onshore in droves. In addition to the West Coast of North America, Velella have washed up on beaches of the Mediterranean Basin, the Galápagos Islands, and Great Britain.

“We don’t believe that stranding of these guys is indicative of the species in trouble,” said Parrish. “They are signaling that there’s a change in the environment.”

Between 2003 and 2006 and 2014 and 2019, the temperature of the sea surface off the U.S. West Coast was up to 2℃ warmer than average during the winter. Consequently, V. velella washed ashore the following spring each year. Parrish and her colleagues saw reports of the jellyfish from Northern California’s Cape Mendocino to the Canadian border.

“They literally carpet the wrack line for a thousand kilometers,” said Parrish.

According to a study by Parrish published this month in Marine Ecology Progress Series, the strandings happened most frequently between mid-March and mid-April and concentrated near the outlet of the Columbia River. Sporadic strandings happen in the fall, too. The data were collected by community volunteers through the Coastal Observation and Seabird Survey Team.

Parrish guesses that the jellyfish populations spiked in warm years because they had more to eat. V. velella love munching on northern anchovy eggs, which become more common in warm seasons. Without more research, however, scientists can’t say for sure what’s driving the surge in Velella strandings.

Along for the Ride

“There’s still a lack of data about the environmental factors driving the occurrence or bloom development,” said Rita Pires, a scientist at the Portuguese Institute of the Sea and Atmosphere in Algés who was not involved in the work.

V. velella on the beach
V. velella are so delicate that only days after washing ashore, they dry into crispy white flakes and break apart. It is still unclear whether a spike in jellies during warm years could affect the availability of food in the ocean. Credit: COASST

But this research gives scientists useful indications on what conditions affect similar species, like the Portuguese man-of-war, Pires said. “From my experience, in periods when both species are reproducing…they are frequently found together in the beach strandings.” Man-of-war stings can be fatal, and sightings shut down beaches.

Shin-ichi Uye, a professor who studies jellyfish at Hiroshima University who was not involved in the research, said that mass strandings represent change on the surface of the ocean.

“If global warming continues,” Uye said, “V. velella standings will be more widespread and prevalent.”

If so, Parrish said the jellies might benefit from climate change. “It’s moving into the position of being a winner.”

—Jenessa Duncombe (@jrdscience), Staff Writer

Citation: Duncombe, J. (2021), Why trillions of jellyfish washed ashore from Canada to California, Eos, 102, https://doi.org/10.1029/2021EO156621. Published on 31 March 2021.
Text © 2021. AGU. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.