The sudden appearance of thousands of small, vibrant blue creatures scattered across the shoreline can be a surprising sight for beachgoers. These organisms, known scientifically as Velella velella, are more commonly called “By-the-wind sailors” due to their unique method of propulsion. They live their lives far out on the open ocean surface, but certain weather patterns bring vast numbers of their flotillas to the coast. The primary question that arises when encountering these gelatinous bodies is whether this strange, marine life poses any threat to human health.
Assessing the Risk to Humans
Concerns about danger often arise because Velella velella are relatives of jellyfish and other stinging animals. They possess specialized stinging cells (nematocysts) whose venom is designed to paralyze microscopic prey. These nematocysts are generally too small and weak to effectively penetrate the comparatively thick outer layer of human skin. Direct contact with the organism, even a stranded one, typically results in no reaction for most people.
Individuals with highly sensitive skin or an allergic predisposition may experience a mild irritation or tingling sensation. Rinsing the area with saltwater is recommended, though medical intervention is almost never required. It is prudent to avoid touching sensitive areas like the eyes or mouth after handling a By-the-wind sailor, as residual stinging cells can irritate mucous membranes. Pets, particularly dogs, should be prevented from ingesting stranded animals, as consumption can lead to stomach upset.
Biology of the By-the-Wind Sailor
Despite their jellyfish-like appearance, Velella velella are categorized as a type of hydrozoan within the phylum Cnidaria. Unlike a single, free-swimming jellyfish, each By-the-wind sailor is a colonial organism. This means the organism is an aggregate of many genetically identical, tiny individuals, or zooids, that are physically connected and specialize in distinct functions.
These zooids are divided into groups dedicated to feeding, reproduction, and defense. The entire colony is supported by a flat, oval-shaped, chitinous float that provides buoyancy and is typically one to three inches in diameter. Extending upward from this float is a thin, rigid, semicircular sail that facilitates passive movement. The colony also maintains a symbiotic relationship with photosynthetic algae, known as zooxanthellae, which live in their tissues and supplement their diet.
Why Velella Velella Wash Up En Masse
Mass beaching events are a direct consequence of their reliance on surface currents and wind. As passive floaters, they have no independent means of propulsion or steering. They spend their lives in large offshore aggregations, or flotillas, as part of the neuston—the community of organisms that live at the water-air interface.
A prolonged period of sustained onshore winds is the primary factor in a stranding event, physically pushing the surface population toward the coastline. The population is split into two distinct morphological types: those possessing a right-angled sail and those with a left-angled sail. This adaptation causes the two groups to sail at a slight angle to the wind, ensuring that at least one portion of the population will be blown away from the shore, preventing total annihilation. Once deposited on the sand, the organisms quickly dry out and perish, eventually leaving behind only a transparent, papery remnant of their float.