By-the-wind Sailor

millionsSince April, hordes of bright blue jellies have been stranding themselves on the Pacific coast. Reports from Oregon and Washington started washing in mid-April with numbers of jellies in the thousands. They swept down the coast to northern California where reported abundances reached millions. When the jellies surfed into southern California in early May, news stories claimed billions of cookie-sized azure animals carpeted the shoreline. Not just beaches, but coastal waters have been inundated. The Columbia River sector of the Coast Guard has responded to nine potential oil spills that turned out to be floating armadas of indigo jellies.

Southward journey of the blue jellies
Southward journey of the blue jellies

The species of jelly blanketing the Pacific coast goes by a number of names, all equally poetic. The Latin name of this animal is the melodic Velella velella, which means “little sail,” and that’s one of the common names of the creature too. But it also goes by purple sail or blue sailor or, my favorite, by-the-wind sailor. All of these names refer to the structure that sticks up from the surface of the water. It’s an air-filled chamber that acts as both a float and a sail, catching the wind.

Velella’s sail is a nautical marvel. Although paper thin, its triangular shape ensures it doesn’t collapse in the wind the way that a square shape would. And if you look at it from the top, it is set into its base with an “S” shape. As you know from pinwheels, concave surfaces catch wind better than flat surfaces. Because there’s a concave surface on both sides of the sail, the jellyfish can catch a breeze equally well from either side.velella-velella-7641

The sail itself isn’t set into its elliptical base straight down the center, but at a diagonal. As a population, about half of Velella’s sails are angled a bit to the left and the other half are angled to the right. When the wind blows, half the jellies sail at angles to the left of the wind direction and the other half at angles to the right. This difference disperses the species throughout the ocean, and when the wind blows along the shore, it ensures that at least half of them end up out to sea rather than stranded on beaches.

Beyond its sophisticated rigging, the sail has still another exceptional purpose. Although it is afloat, the by-the-wind sailor is not a medusa. Instead, its anatomy resembles the anemone-like sedentary stage that’s usually found glued upside down on a rock or a shell. In the open ocean, overhanging hard surfaces are hard to come by; there aren’t that many upturned shells or caves. But the by-the-wind-sailor’s buoyant sail is an innovation that allows it to colonize the biggest surface in all the sea: the surface between the water and the air.

By-the-wind-sailor medusae
Bead-sized by-the-wind-sailor medusae

Velella hails from a family of jellies called hydrozoans, and its particular clan lives in colonies of many individuals. The mouth is located underneath the sail’s base, facing downward into the ocean. Around the outside of base, tentacles with stinging cells reach into the sea. The space between the mouth and the tentacles is inhabited by various members of the colony, some with their own mouths, others with their own stinging cells, and some that produce greenish bead-like medusae, just one-tenth of an inch in size, which swim free of the mother-ship Velalla. The medusae then produce eggs and sperm, which, after a stint as a larva, grow into another full-fledged by-the-wind sailor hanging upside down attached to the surface of the sea.

Nick Bond’s rendering of the hot blob a year ago, soon after  it got its start. SST stands for sea surface temperature and the orange region is about 4 degrees F above normal.

On reason for the recent strandings is a spate of strong winds along the Pacific coast driving the jellies onshore. But a bigger oceanic phenomenon also at work probably helped boost the size of the population to begin with.

Beginning in the fall of 2013, Washington State climatologist Nick Bond noticed a “blob” of unusually warm water—and, yes, “blob” has become the technical term for this steamy mass—hanging off the West Coast. It started as a circular shape about 1,000 miles in diameter anchored off Washington. During 2014, it morphed so that it slithered all the way down the coast to Mexico.

The blob probably started when a high-pressure system stalled out over the Pacific Ocean, leading to calmer seas. Like stirring a bowl of soup to cool it, rough seas release heat. Without stirring, the opposite happened; calmer winter seas held in heat, raising the temperatures in the blob nearly 4 degrees Fahrenheit above normal.

The hot blob has a number of consequences for the West Coast. Warm water holds fewer nutrients than colder water, stunting the base of the food web, which has repercussions all the way up to the fish and seals. Fish catch in Puget Sound has plummeted. Starving baby sea lions have been found in record numbers along California this year. The blob also exacerbates the drought plaguing California warming weather systems that might otherwise produce needed mountain snowpack. And tellingly, warm water-loving organisms, like jellyfish including Velella, have a sudden advantage over creatures adapted to colder climes.

While this blob isn’t caused by climate change, it is a kind of dress rehearsal. “This is a taste of what the ocean will be like in future decades,” Washington climatologist Nick Bond said. “It’s producing conditions that we think are going to be more common with global warming.”

Looks like there’ll be more clear sailing for Velella.

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