WATCH: The secret life of Velella jellyfish

Steve Haddock of the the Monterey Bay Aquarium Research Institute (and author of the fantastic book, Practical Computing for Biologists) sent me a link to MBARI's latest video, about the wonderfully weird Velella jellyfish, aka the by-the-wind sailor.

In the spring, beaches can be covered by thousands or even millions of blue jellyfish relatives called Velella velella, the by-the-wind sailors. Velella typically live on the surface of the open ocean far from shore, propelled by winds pushing on their tiny sails.

Velella is best described as a hydroid colony which has flipped itself over. It is unlike a traditional jellyfish (medusa), but rather like the benthic stage of a hydroid. Instead of living attached to rocks on the bottom, its "substrate" is the ocean's surface. These hydroid colonies bud off tiny medusae, little "jellyfish", just like many benthic hydroids do.

A particularly striking feature of Velella is their blue pigmentation. In fact, most animals that live on the surface of the water (snails, jellies, fish) have blue pigmentation. It may serve different purposes for different organisms, but is likely a combination of camouflage and protection from the sun's rays.

For more information on Velella and to report your own sightings go to

Notable Replies

  1. What beautiful animals. I've read about Velella, but it's always seemed to me like an under-studied and under-photographed cnidarian. I have a book about jellyfish, but Velella is only drawn--and I think it's hard for pictures to capture just how interesting it is. The Portuguese man-o'-war, which is much more likely to sting humans, hogs the spotlight.

  2. It is unlike a traditional jellyfish (medusa), but rather like the benthic stage of a hydroid.

    I bet that's the secret. I have no idea what it means. It's one of those loopy curves from trig class, right?

  3. Something I think is kind of interesting is that while many of the animals are blue, it happens in different ways. There are different pigments in even by-the-wind sailors and man-o'-wars.

    Not everyone pronounces Latin the same way, but in English there's a traditional version where you anglicize single vowels, and only say the second part of most double vowels. That's how you get the "aye" in words like alumni and the long "ee" in words like phoenix or Caesar, in reverse of the classical sounds.

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