Are you ready to be swept away by the captivating world of by-the-wind sailors? These mesmerizing species glide on the surface of the ocean and have some truly remarkable characteristics. From their stunning appearance to their unique behavior, let’s dive into some fascinating facts about them!
Phylum: Cnidaria
Class: Hydrozoa
Order: Anthoathecata
Family: Porpitidae
Genus: Velella
1. They look like a sail
The by-the-wind sailor, also called little sail, purple sail, or sea rafts, is one of the most unique creatures in the ocean. Like the Portuguese man o’ war and the blue button, they are colonies of many individual animals.
By-the-wind sailors have a flat and oval-shaped body that can reach up to six or seven centimeters in diameter. Positioned atop the body is a small, semi-circular sail made of chitin, consisting of concentric tubes that are filled with gas. This unique feature enables the wind to drive them along the ocean’s surface.
Because of the sail-like float, the species are called ‘by-the-wind sailors’. These creatures are subject to the whims of the wind and are often discovered washed up in groups of hundreds or even thousands following stormy winter weather.
These creatures exhibit handedness, or sailing preference, which determines their downwind trajectory at a 45-degree angle to the left or right of the wind. This behavior often causes a population divide in two, giving them an advantage. In strong winds, only half of the population may become beached.
The interesting thing is that their 45-degree angle sail closely aligns with the optimal angle at which a sailing boat can traverse. This is also the greatest angle at which yachts may sail upwind.
Below the disk is small short tentacles that extend downward into the water to balance the body, allowing the sail to work much like a keel on a yacht. These tentacles are packed in stinging cells called nematocysts. Although these stings are typically harmless to humans, there may be an occasional allergic reaction.
By-the-wind sailors are predominantly composed of water and are relatively lightweight. Additionally, their size can vary significantly and rapidly, depending on food availability.
2. Distribution and habitat
By-the-wind sailor jellyfish can be found in temperate and tropical seas. These species often spend their whole lives in the middle of the ocean. They are frequently sighted by passing ships in large numbers.
They are a widely distributed species, drifting with ocean currents and wind in practically every ocean. Although they occasionally wash up on land, this usually happens along the Northwestern Coast of the United States, particularly in Oregon.
Like the blue button and man o’ war jellyfish, by-the-wind sailors float on the sea surface and are susceptible to sunburn. However, their vivid blue hue serves as a natural sunblock, shielding the colony from harmful solar radiation. Additionally, this color provides the animal with camouflage, allowing it to blend in with its environment and avoid predators.
3. They eat solar energy
By-the-wind sailors primarily feed on small species found at or near the surface of the ocean. Their diet includes larvae, copepods, zooplankton, and fish eggs. They can also eat other small species because they are not picky eaters due to their passive nature.
These sailors hunt passively. As they drift along, their tentacles, which are lined with venomous stinging cells, shock and capture their prey. Then, they carry the food to their mouth in the center of their body for digestion. Like other Cnidarian members, by-the-wind sailors do not have a separate mouth and anus. They eat and waste at the same place. Gross!
If the creatures can’t get any food, they use their backup plan. If you look closely at their body, you’ll notice a golden-brown coloration. This color is a type of algae called zooxanthellae. These little sails and zooxanthellae have a win-win relationship.
The zooxanthellae live within the purple sail, consuming the waste it releases. In exchange, the algae will nourish the host by converting sunlight into sugars that the sail can use as energy. This mutually beneficial relationship allows both organisms to thrive.
By-the-wind sailors are preyed upon by some natural predators, such as blue dragon sea slugs, purple snails, and sunfish (Mola mola).
4. By-the-wind sailor vs Portuguese man-of-war
| By-the-wind sailors | Man O’ Wars | |
| Size | smaller | bigger |
| Color | blue | translucent with shades of pink, blue, and purple |
| Appearance | round disk with a thin sail on top and tiny tentacles | ballon float with very long tentacles |
| Sting | harmless | very painful and can kill humans |
5. Reproduction
Every polyp on a single sailor jelly is either female or male. They use their mouth-like reproductive organs, which are covered by stinging tentacles, for reproduction.
By-the-wind sailors engage in asexual reproduction by budding, whereby they generate clones of themselves. These clones subsequently detach, forming medusae. A single parent can produce numerous medusae throughout their lifetime, ranging from hundreds to thousands.
The medusae, resembling miniature jellyfish, are exact replicas of their parents in terms of genetics. At birth, they measure less than 2 millimeters in length, which is just half the size of a grain of rice.
These tiny creatures drift along until they encounter other compatible polyps, with which they combine to form a colony. Unfortunately, only a small fraction of them manage to make it to their juvenile and adult stages. The lifespan of the by-the-wind sailor is still a mystery.
6. Threat
These sails are facing several significant hazards, such as rising ocean temperatures, acidity, and elevated human activities in oceanic and coastal regions. Microplastics are also a concern to the animals because they can absorb microscopic particles of floating plastic, which can negatively impact their health.
References:
- https://seaunseen.com/velella/
- https://marinesanctuary.org/blog/sea-wonder-by-the-wind-sailor/
