Mass Velella stranding covers beaches in Ventura County, California
Thousands of Velella velella, also known as by-the-wind sailors, washed ashore on beaches in Ventura County, California, from late April to early May 2025. The mass stranding, driven by onshore winds and warm ocean conditions, reflects seasonal oceanographic changes along the California coast.
Velella velella & Palmaria palmata, Moonstone Beach, Cambria, California. Image credit: Peter D. Tillman/Wikimedia Commons
From late April to early May 2025, thousands of Velella velella hydrozoans stranded on Ventura County beaches, including Channel Islands Harbor, Silver Strand, Hollywood Beach, and Kiddie Beach. These 7.6–10.2 cm (3–4 inch) blue-purple organisms, resembling jellyfish, form floating colonies that can appear “like an oil slick” from a distance. Their mass presence along the shoreline surprised beachgoers.
Velella velella, a neustonic hydrozoan, floats on the ocean surface using a small, translucent sail. According to the National Park Service, the sail’s angle determines whether the organism is right- or left-handed, with most Northern Hemisphere Velellas being left-handed. Their blue tentacles contain mild stinging cells used to catch plankton, including zooplankton and fish eggs.
The strandings occurred due to strong onshore winds from coastal storms or sea breezes that pushed floating Velella colonies ashore. Springtime upwelling, which brings nutrient-rich water to the surface, supports the plankton blooms that Velella feed on. Raphael Kudela, a marine scientist at UC Santa Cruz, told KQED, “In the spring is when we have upwelling… lots of nutrients bring phytoplankton and zooplankton.”
Warmer-than-average sea surface temperatures in winter–spring 2024 occurred before the mass strandings and correlated with increased Velella populations offshore.
“When we see signals coming from the ocean to the coast, we should pay attention. The Velella velella is an early warning bell that we may be seeing some shifts,” Julia Parrish from the University of Washington, analyzing two decades of citizen-science data, told KQED.
Once stranded, Velellas dry out, lose their vivid blue color, and resemble ‘brittle cellophane candy wrappers,’ according to the National Park Service. Channel Islands Harbor issued a warning via FOX LA, advising the public to avoid direct contact as stingers may irritate the skin: “Avoid touching your face after handling one.” Though not usually dangerous, contact with the eyes or mouth should be avoided.
Past strandings occurred in 2002–2003, 2014–2015, and 2023, displaying similar conditions. In April 2015, trillions of Velellas were recorded over a 1 000 km (620 mile) stretch from Washington to California, according to University of Washington research. NOAA Fisheries reported that global strandings, including one in Sardinia in 2024, align with warm winter sea surface temperatures: “Mass strandings are more prevalent in years with warmer-than-average winter sea surface temperatures.”
Citizen-science initiatives such as COASST have compiled the world’s most extensive dataset on Velella, including 465 reports from 293 beaches. “Thousands of trained, dedicated observers are better than any satellite because they know their beach and can alert us if something is weird or unusual,” Parrish told UW News. In 2019, the absence of Velella in Oregon was noted by volunteers, prompting further investigation.
Anya Stajner of the Scripps Institution told KGTV that Velella strandings offer research opportunities into ecological roles and potential medical compounds.
“There’s lots of opportunity to learn about animals that affect our ecosystems… maybe [compounds] for medicine… it’s important to stay curious and invest.”
Velella may compete with forage fish such as sardines for plankton, which could influence fisheries. “They provide a window of wonder and awe to the great ocean… and how much we know and don’t know about the largest habitat on the planet,” Jennifer Stock of NOAA told SFGATE.
Predators of Velella include nudibranchs, purple sea snails, and ocean sunfish. While not harmful, Velella strandings reflect environmental conditions such as wind, ocean currents, and sea temperatures.
Reet is a science journalist and researcher with a keen focus on extreme weather, space phenomena, and climate-related issues. With a strong foundation in astronomy and a history of environmental activism, she approaches every story with a sharp scientific lens and a deep sense of purpose. Driven by a lifelong love for writing, and a curiosity about the universe, Reet brings urgency and insight to some of the most important scientific developments of our time.
Fascinating stuff. A few years back, on beaches near Ocean Shores, Washington, just about this time of year I observed this phenomenon first hand. Because I am a supporter of the Oregon Shores Conservation Coalition, I always report these findings to them. Citizen scientist observers are indeed of critical value in recording these sightings. Thanks for this article!
C’est triste
Thanks Tanya!