I first heard of this animal when I was browsing one of my favourite websites – and for once it wasn’t the name that caught my attention (even though it’s an excellent one). There was a picture of it, and this is definitely a weird looking animal! So then of course I had to learn more about it, and although what I read is mostly confusing, I’ll do my best to share it with you!
The by-the-wind sailor is a remarkable species. When it was first classified, scientists thought the by-the-wind sailor was composed of a colony of hydrozoans (tiny jellyfish like creatures), much like the Portuguese man-o-war. This was amended by later studies, which reclassified the sailor as simply a large and highly modified individual hydrozoan. Turns out the old guys were right, and the by-the-wind sailor is made up of hundreds of tiny little creatures.
Each of the parts of the sailor have a specialized function, much like cells in our bodies. These are connected through canals which allow the colony to share food and other resources. Tentacled hydrozoans called gastrozooids are the feeding animals, grabbing plankton and other small animals with their tentacles. Gonozooids take care of breeding; they spend all their time releasing tiny medusas into the water. Medusas are the sexually reproductive stage of the sailor, with polyps being the other stage. Medusas are produced asexually by budding, and then drift around and release eggs and sperm (depending on their sex) to produce larvae which develop into a new colony. The way medusas get energy is pretty awesome – the colony provides each medusa with lots of zooxanthellae, single celled organisms that get energy from the sun and give it to the tiny jellyfish.
I guess you’re probably wondering why it’s called the by-the-wind sailor. Basically it’s just a very descriptive name. These jellies stay on the surface of the water their whole lives, except during the larval stage. They have a little ‘sail’ on top of their float, which catches the wind and bears them willy nilly across the seas. Well, that’s not exactly true – the orientation of the sail is very important in determining where the sailors go. The sail is oriented northwest to southeast along the long axis of the sailor’s body in the eastern side of the Pacific, while the opposite occurs on the western half of the ocean. Rather than being a result of geographic distribution, it is thought that by-the-wind sailor originates in the middle of the pacific, where winds sort them out by sail orientation. Which I think is really cool. The sailor is so at the mercy of the wind that mass strandings often occur, when strong offshore winds force the animals onto beaches. These can be so large that the carpet of jellyfish is centimetres deep. I would definitely not want to go to the beach that day.
The by-the-wind sailor is nature’s original drifter – and they’re pretty good at it. I’m a little jealous of them. Sometimes I’d like to just ride the wind and see where it takes me. I guess I’ll have to grow a sail.
Cover By Ruth Hartnup from Vancouver, Canada – By-the-wind sailor at Mackenzie Beach, CC BY 2.0