Micronesia's "Golden Bowl"
Located in the island country of Palau, in Micronesia, Jellyfish Lake looks at first glance like just another tropical lagoon. Just below the surface, though, a natural wonder awaits: millions of mastigias papua— golden jellyfish, or medusae—dangling in the water like constellations of shining bulbs.
The jellyfish were swept in about 12,000 years ago, when sea levels rose near the end of the ice age and flooded dry land. Jellyfish Lake is a marine lake, landlocked but connected to the ocean via underground limestone channels, and one of dozens in Palau's Rock Islands. (Of the five marine lakes there that contain jellyfish, it is the only one open to visitors.)
Jellyfish Lake's 13 million or so golden medusae have a curious daily routine. Each morning, they move eastward across the lake, following the sun's path. This migration keeps them at a safe remove from their primary predators, shade-dwelling anemones; it also allows the microscopic algae that live in the jellyfish to absorb precious sunlight, thereby providing energy for themselves and their hosts.
It is commonly believed that over the years, these predator-avoiding jellyfish have lost their ability to sting. In fact, they do sting—just rarely strongly enough to be felt by humans. They are delicate enough to be destroyed by a careless snorkeler's kick. Contrary to their namesake, these medusae aren't exactly ugly—especially en masse, pulsing in clear blue waters.