Jellyfish Lake, one of many marine lakes found on Eil Malk island in Palau, certainly lives up to its name. Eil Malk is part of a group of mostly uninhabited, small, rocky islands known as the Rock Islands. Although there are more than 70 marine lakes scattered across the Rock Islands, this one has become famous as a snorkeling paradise. As long as you aren't bothered by millions of golden jellyfish that migrate horizontally across the lake daily, then this is the place for you!
The lake is around 12,000 years old and is estimated to be 30 meters deep. Jellyfish Lake is linked with the ocean through tunnels in the limestone of ancient Miocene reef. Although there is a connection, the lake is still very isolated and the conditions are unique enough that the diversity of species within the lake have been greatly reduced from the nearby lagoon.
Two species of jellyfish occupy the lake: Golden Jellyfish, shown above, and Moon Jellyfish. Both species are known for their rigid daily migratory patterns. For around 14 hours during the night the Golden Jellyfish make repeated vertical excursions between the surface and the western basin, perhaps in search for nutrients near the chemocline. From early morning until 09:30 they move from the western basin to the eastern basin. From early afternoon until about 15:30 they move from the eastern basin to the western end of the lake. As the sun sets they head to the western basin, where they will remain for the night. The Moon Jellyfish do not exhibit specific horizontal migratory paths, and simply migrate up towards the surface to feed at night.
In late 1998 the Golden Jellyfish population suddenly began plummeting, and by December the medusa population had declined to zero. This was attributed to warming water temperatures due to an El Nino weather event, which killed off all the algae (the jellyfish's primary source of food). Today the Golden Jellyfish population has bounced back and is at pre-decline levels.