Velella velella, commonly known as by-the-wind sailors, are marine organisms often encountered floating on the ocean’s surface. Their distinctive appearance and presence at the air-sea interface make them visible to beachgoers and sailors alike.
What Exactly Are They?
Velella velella are hydrozoans within the phylum Cnidaria, not true jellyfish. They are colonial organisms, meaning each “individual” is a collection of specialized polyps living together. These polyps are connected by a shared canal system and have distinct roles, including feeding, reproduction, and defense.
Their physical structure is well-adapted for life at the ocean’s surface. The body consists of a flat, oval float, typically deep blue to purple. This float, usually less than 7 cm long, has gas-filled chambers that provide buoyancy. A prominent, upright, triangular “sail” extends diagonally from the top of the float, giving the creature its common name.
Their Unique Ocean Life
By-the-wind sailors inhabit pelagic, or open ocean, environments across warm and temperate waters worldwide. They live at the air-water interface, a specialized habitat. Their rigid, chitinous sail catches the wind, propelling them across the ocean surface and making them entirely dependent on wind patterns for movement.
These creatures are carnivorous, relying on tentacles to capture food. These tentacles, hanging from the float, possess stinging cells called nematocysts. They use these cells to paralyze small zooplankton and fish eggs. By-the-wind sailors serve as both predators and prey, being consumed by specialized marine snails and nudibranchs.
When They Wash Ashore
By-the-wind sailors commonly wash ashore, particularly along coastlines like the Pacific Northwest. This phenomenon occurs when strong winds and currents push large aggregations of these surface-dwelling organisms towards the land. Mass strandings are especially frequent in spring and early summer, and warmer ocean temperatures can correlate with increased events.
When Velella velella are stranded on beaches, they dry out and lose their vibrant blue color, becoming transparent and brittle, resembling cellophane. Their sting is typically benign to humans, causing only mild or no irritation upon contact. It is advised not to touch them, and to leave them undisturbed if found on the beach. Even after stranding, they can still serve as a food source for some scavenging marine animals.