While other well-known “true jellies”, like the Moon Jelly, are "neutrally buoyant" (meaning they neither float or sink), hydrozoans float on the surface of the water. They have no way of propelling themselves through the water, instead relying solely upon the wind and ocean currents to carry them while they sweep their hanging tentacles into microscopic prey for them to eat. (While the Sailors' stings may be dangerous to the planktonic organisms they feed on, they are not harmful to humans.)

 

It is believed that warmer-than-average winters result in significant population increases, meaning that Sailors exist in greater numbers during El Nino years like 2024. During early spring, strong winds blow from the northwest, leading this army of small jellies slowly and perilously closer to shore. They have been washing up in large numbers along the north coast since February, and the California current has been slowly pushing them down the coast, blanketing the beaches in their wake. Within the last few weeks, they have finally reached the end of their journey in Southern California. It is likely they will continue to wash ashore into June. Ultimately, the warming summer waters will lead to a die-off of many of the remaining Sailors, while the weakening of the winds means that the rest of the Sailors will simply stay restricted to their offshore habitat.

While this mass beaching may be an inconvenience to beachgoers, at least some local wildlife benefits from the large influx of Sailors. The Ocean Sunfish, Mola mola, is an odd fish with a strange disk-shaped body and thick leathery skin. They are better known for their clumsiness and immense size, making it difficult for them to chase down and catch anything with a brain. Luckily for them, By-The-Wind Sailors not only lack a brain, but any way to move their body. As such, they are an easy snack for a hungry Sunfish. The Sunfish have been frequently spotted eating thousands of Sailors per day, rising up and scooping two or three at a time off the sea surface.

If you see By-The-Wind Sailors on the beach, it's fun to look at them and wonder what kind of journey they had before reaching Manhattan Beach. But even though they won't sting you, you should generally avoid touching them. They'll eventually disintegrate and get washed, circle-of-life style, back into the ocean.

Zachary Fratello is a junior at Da Vinci Science High School. He is conducting research on local fish populations as part of the Southern California Academy of Sciences' Research Training Program.