Masses of ephemeral organisms called “sea-men” wash up on the West Coast every year in the form of a “blue tide,” but warmer seas are increasing their numbers.
From Oregon to California, blankets of blue, alien-looking creatures are washing up on rocky beaches. They are Velella velella, colonies of organisms with a hat-like body and dangling tentacles.
Captivating thousands along the US West Coast this week, much delight was in the air among beachgoers who gleefully posted pictures on social media. The blue tide is what they call it, although they do not always refer to the same abundance level.
Alien-looking creatures
Velellas, also called “sea-men,” are colonies of creatures of a certain freshwater class called hydrozoa. Though they look like one organism, they are not. They spend most of their lives in the open ocean, in the water column below them with tentacles that catch fish larvae or zooplankton, but they are integrated. One part of the colony is responsible for reproduction and another for breeding. Coral is another colonial organism, but it is rare to find such colonies on land, says Anya Stajner, a doctoral student at the Scripps Institution of Oceanography.
There are a few theories about how the animals got their bright blue color. The interaction between air and ocean doesn’t offer them many places to hide from predators, such as the huge mola sunfish, which sucks on velella like it’s candy. Their color might help them cover themselves from the waves, Stajner says. Another advantage is that the color protects them from ultraviolet rays, which is a kind of sunscreen.
Velella live for months and travel throughout the Pacific Gyre, says Julia Parrish, a marine biologist at the University of Washington. They typically travel up the California coast to the United States, then dart past Hawaii to Japan and back again, gliding across the surface like a kite surfer.
The creatures go through boom and bust cycles along this journey, experiencing many life stages, “which are all quite different from each other,” Parrish says. While there is plenty of food in the water column for them, their population explodes and they wash ashore together, often occurring during the spring and spring.
Despite being frequently encountered by humans, velellas are not a widely studied species, in part because of their way of life. Marine biologists have had much success developing jellyfish tanks, for scientific research and for the public to see them up close. But velellas remain at the sea surface and have plenty of resources throughout their lives, and scientists have not yet solved the problem of how to create the conditions to breed them in captivity. This means we know less about them than we do about most jellyfish that live underwater, away from human eyes.
One area of recent study is the relationship between velella and ocean temperatures. In 2021, Parrish used data collected over two decades of citizen scientist observations to tease out the patterns in velella mass chains and found that the events were much more likely to occur when waters were warmer than normal.
The reasons are still being investigated, but Parrish thinks it has something to do with rough seas. “In stormy waters with very high waves that sustain for several days, like in hurricanes, colonies that are just small and start to expand easily are on the verge of being torn apart,” Parrish says. Consequently, the Velella had foamed a little less and thus more integrated, permitting them to fight a better fight for themselves and become survivors towards the end stages. This again left behind several colonies for further growth.
The tiny embedded mariners are ephemeral by nature, not following the same patterns each year. But when they do appear in large numbers, it typically happens in more than one place at the same time, Parrish says.
The creatures form a hill-like vista when washing ashore that attracts both photographers and beachgoers, but they will lose pigmentation when dried and compare to ‘crunchy potato chips or candy wrappers,’ Stajner says. It is speculation now but could play a role in carbon and oceanic internment that otherwise would probably remain in the ocean they were washed into.
Swim-goers love them because they are adorable, easy to recognize, and found in large numbers. Admirers, however, may not realize they are building colonies of creatures that are embedded and dead, Parrish says. “Instead, what you see is a fish that is beautifully colorful, small enough to be built, and is built and built-integrated,” he adds.
As the world’s oceans continue to warm as part of the climate crisis, more velella colonies are likely to come ashore and thrive in the sea as well. This has Parrish scientists wondering if these charismatic little blue-hatted creatures might have a more complex effect on the oceans than we think. Because velella consumes zooplankton, fish larvae, and fish eggs, they could negatively impact fish species.
“There is some evidence that collectively there are enough hungry Velella to replace the dynamics of the populations of a few classes of forage fish, like anchovies, also on the east coast of California,” says Parrish.