Jellyfish Lake. Palau
This lake is one of the most amazing phenomena in nature. One small Jellyfish Lake or “Ongeim’l Tketau” teems with ten million of wonderful jellyfish. It is home to two species of jellyfish: gold and moon. Here you can see the giant jellyfish with size of more than a soccer ball, and such tiny as a fingernail. The physiology of jellyfish is quite primitive. The body of jellyfish contains eight eyes and the algae that live within their cells.
This unusual marine lake is located in the eastern part of the densely wooded Eil Malk Island in Palau. The size of the reservoir is 460 m by 160 m, surface area – 0,057 sq km and a depth of 50 m. The lake was formed 12 thousand years ago, as a result of crustal movements. One of the flooded reefs rose above sea level and corked small saltwater lake inside the island. Jellyfish accidentally got into this place and began to multiply freely. There were no other inhabitants in the lake, there were no predators, so the jellyfish gradually lost their burning hairs. They just didn’t need them anymore. Therefore, they are absolutely harmless. Diving enthusiasts can safely swim in the lake and admire the jellyfish, being not afraid to get a nasty burn.
The water in the Jellyfish Lake is salty. The lake is connected with the Pacific Ocean by a network of cracks and three small tunnels, penetrating the surrounding limestone. But the living conditions are absolutely not similar to the ocean. Therefore, these jellyfish are very different from their relatives that live in the lagoon of the ocean in only 200 meters.
The algae require sunlight. They need it to grow and develop. This factor makes the jellyfish move all the time following the sun. It is unimaginable spectacle, when all this mass of jellylike jellyfish crosses the marine lake twice a day, from one bank to another, in order to follow the sun. When night falls, mostly golden jellyfish rush to the depth. Water on the bottom of the lake is rich in nitrogen. Moon jellyfish spend the night at the water surface, where they can catch copepods.
The water in the Jellyfish Lake is clearly divided into two layers – top and bottom. The oxygen content in the top layer is much greater than in the lower. At a depth of 15m the content of oxygen in water decreases to zero. The top and the bottom layers of the lake are never mixed. Thanks to the tunnels, which connect the lake with the ocean, the top layer of the lake is provided by the flow of a small amount of fresh water. But only the top. All the main inhabitants of the lake can be found only in the upper layer of water. The water of the lower layer is strongly saturated with hydrogen sulphide, ammonia and phosphates. This represents a threat to most living creatures. Man can get serious poisoning directly through the skin.
Golden jellyfish are the most numerous inhabitants of the lake. They are practically unique! These jellyfish have lost their pigment spots, and almost completely lost the ability to sting. Furthermore, they have other distinctions in body structure, which make them different from ocean jellyfish of the same species. Some biologists propose to allocate the golden jellyfish living in the lake in a separate subspecies.
The picturesque accumulation of jellyfish in the lake attracts a lot of tourists and diving enthusiasts.