Occasionally, by-the-wind-sailor jelly fish (Velella velella) wash up in droves. Sanctuary beaches have seen lots of these blue jellies in spring 2002 and April through August, 2003. On the surface of the water, large aggregations of these animals look like oil slicks. Once washed ashore, the blue color fades and they look like fields of crumpled cellophane. Velella velella are found around the world.

Their triangular "sail" is angled so that the wind usually keeps them offshore, but when strong winds blow, they lose their ability to "tack" and wind up on our beaches. Within a population, there are individuals whose sails are oriented in different directions. These "mirror image" jellies get pushed in opposite directions by the wind.

The blue-pigmented float is made of gas chambers that are used for buoyancy. Small tentacles hang down from the float and contain stinging cells. Though these jellies are not dangerous to humans, it is recommended to not touch eyes or mouth after handling them. These floating jellies eat fish and invertebrate eggs, as well as copepods, and are eaten by ocean sunfish.