Welcome to the weird and wonderful world of Jellyfish Lake.
This marine lake is situated on Eil Malk, an island in Palau, in the Pacific Ocean. It is encased by limestone, and hence fractures and fissures within the rock structure have allowed for the intrusion of seawater, which is just a few metres away.
Each day the Golden Jellyfish journey vertically down to a lower level of water (known as the chemocline) – presumably to gather nutrients. Then they cross the lake throughout the day, from the western to eastern basin in the morning and back across in the afternoon. The reason for this daily migration is thought to be associated with increasing the potential of sunlight reaching the symbiotic zooxanthellae that they host. Another reason is accredited to their predator; anemones. Anemones do not like intense sunlight and hence lurk in the shadows. By avoiding the shadows for the most part of the day, the jellyfish are less vulnerable to attack.
You may be wondering how this person is swimming seemingly carefree among them?
Although both species in the lake possess stinging cells, they are not powerful enough to cause any harm to humans. This is an evolutionary trait which has developed over millennia due to the relative lack of predators in the area.
The numbers of jellyfish in the lake and the fact that they cannot sting humans, has made this a popular tourist spot. However, there are worries that human interference will disturb this unique habitat. It is understood that air bubbles from snorkels can harm the jellies if it gets caught under their bell- so respect and caution is greatly advised.
-Jean
For more pics, info and a video, go here: http://www.huffingtonpost.com/2011/11/29/jellyfish-lake-palau-video_n_1115577.html