Wildlife Spotlight: By-the-Wind Sailor (Velella velella)

By Stefan Marti
Published: April 2007

Clear sail of velella. Credit: Curt Beebe

Imagine you are scuba diving in the middle of the Pacific Ocean, you surface and become a tiny blue boat with a lone sail.  Weeks go by, months, as you drift with the winds, until one day you spot dry land on the horizon.  The final gusts and waves toss you to shore where you tumble onto the beach to die and disintegrate.  Well, you have just lived the life of Velella velella.

Velella velella, commonly known as “by-the-wind sailor,” is a hydroid polyp—a jelly-like invertebrate.  It is bluish purple in color with a clear oval-shaped float and a triangular sail projecting vertically out of its body.  The sail is uniquely S-shaped (looking down on it), so the organism can catch wind on both sides of its “sheet.”  Like with the sail on a human craft, the pressure gradient will propel the animal on its journey across the ocean.

In late April, hundreds of thousands of these drifting sailors wash up on the beaches of Northern California.  They look like small gobs of cellophane and are generally 5-10 cm long.  For many years scientists believed each individual was actually a colony of specialized polyps, much like the Portuguese man-of-war.  But now general biological consensus is that a single velella is an autonomous organism.

Life at Sea

The velella is a pelagic species, staying on the surface of the open ocean for most of its life.  It never comes close to the sea floor, and the only stage when it is completely submerged underwater is the larval stage.  To remain buoyant in the ocean, it has a series of sealed air chambers in its float.

Velellas can travel in large groups, often thousands of them together.  They have short tentacles with stinging cells that dangle underwater that they use to hunt.  Because they are afloat, they are limited to small prey and fish that swim just below the surface and directly beneath them.  Although their sting is strong enough to stun a tiny animal, a human being would barely feel it.  To make feeding easy, their mouth is located in the middle of their underside.

There are quite a few predators in the sea that feed on velella. Among them are violet snails, sea slugs and ocean sunfish (Mola mola).

The Journey

An amazing thing about these translucent, sci-fi looking creatures is that their destinies are decided at birth with the direction of their sail.  Some have sails going diagonally from northwest to southeast along the length of their body, while others have a sail going from northeast to southwest.  Although they all begin their journeys together in the middle of the warm Pacific, those with a NW-pointing sail will end up on the northeastern Pacific, in places like California, while the others will either head to South America or Asia, depending on the winds.

And if you’re wondering if these ocean travelers panic when they come to the close of their journey and see the shores of our sanctuary, apparently not.  For they have no brain to worry about such things.