Swarms of jellyfish that have appeared recently in the Pacific Northwest and the United Kingdom are not unusual, but may signal an ocean out of balance, experts say.

This summer, huge numbers of blue Velella velella have been washing onto beaches of the Pacific Northwest, where they die and decompose into cellophane-like corpses. The East Coast isn’t immune, either, as moon jellyfish (Aurelia aurita) swarmed off the coast of Maine. The southwestern coast of England has also been hit by explosions of huge barrel jellyfish  MORE