Most of us have heard of “red tides”, those unusually dense blooms of marine algae that stain nearshore waters a brownish red and can be toxic to wildlife and humans. But what about a “blue tide”, when beaches are strewn with an aquamarine layer of jelly-like organisms in spring? These are the innumerable bodies of by-the-wind sailors, and their strandings are a regular yet fascinating phenomenon in coastal Oregon.
Ranging in size from a few millimeters across to seven centimeters, these brilliant blue and purple animals, known formally as Velella velella, are common offshore visitors to the Pacific coast. While they might sometimes wash up on our beaches in alarming quantities, this “blue tide” poses far less of a risk to animals and people than the red variety.
The common name of these gelatinous creatures—by-the-wind sailor—refers to the clear, triangular sail at the top of the animal’s body which catches the wind and propels it across the surface. Short tentacles hang from the underside of the sail. Found in all the world’s oceans, these animals have no independent form of movement and will drift at the whim of the breeze. Their bodies have evolved to capitalize on prevailing winds, which differ depending on season and locality.
On our side of the North Pacific, the sails of Velella are set in a northwest-to-southeast direction, to take advantage of regional wind patterns. On the other side of the North Pacific, the sails are set in a northeast-to-southwest direction—and in the Southern Hemisphere, the sails are reversed. With gentle winds, Velella sail at about a 45-degree angle in front of the wind, aiming always to be blown away from shore.
Despite Velella’s simple yet effective sail, heavier winds during the spring and summer months may nevertheless cause mass strandings of these animals. During such conditions, it isn’t uncommon to see miles and miles of Oregon beach carpeted with stinking heaps of Velella, which quickly die and decay on shore, turning from a metallic blue to a lifeless white.
By-the-wind sailors feed mainly on plankton drifting near the ocean’s surface. They capture these tiny animals by stinging them with barb-tipped cells contained within their tentacles. Their venom is considered harmless to human beings, but beachcombers are cautioned not to touch any jellies or jelly-like animals found washed up on shore, as some may react more strongly to the venom than others. (Other, more dangerous jellies might also be mixed in with Velella.)
Although originally classified as a jelly, current research suggests that by-the-wind sailors are actually a unique species of large hydrozoan (a class of predatory animals, distantly related to corals, sea anemones and jellies, which live mostly in salt water).
By-the-wind-sailors are not singular organisms but in fact colonies of animals. Each Velella is a colony of all-male or all-female individuals (called polyps), which are divided into separate groups within the colony. Some polyps specialize in feeding and reproduction, while others protect the colony and provide structural support. All polyps of an individual Velella are connected by a canal system that distributes food and eliminates wastes.
Visitors walking the beaches this spring should enjoy these incredible creatures safely while their aquamarine hues last—they won’t look that good for long, and they’ll soon smell much worse!