Over 10,000 years ago, as the last ice age ended, sea levels rose and filled depressions in Palau’s limestone islands, which became inland marine lakes. There are around seventy of these lakes in Palau, defined by their salinity, and also their tendency to host unique ecosystems, cut-off from their oceanic roots. The most famous is Jellyfish Lake, known locally as Ongeim’l Tketau, where jellyfish have evolved to worship the sun to survive.
Darwin himself would have been impressed with this fascinating example of evolution. These remote islands in Palau have created these uniquely isolated pools of seawater, catalyzing the evolution of new species. The seafaring ancestors of the Golden jellyfish are the Spotted jellyfish, dragging long stinging tendrils through vast oceanic currents, and devouring masses of plankton.
The Golden jellyfish has evolved to lose those long fishing net like arms, and has developed a symbiotic relationship with a type of plankton which photosynthesizes sugars, which it shares with the jellyfish. To keep the plankton in optimal feeding position, the Golden jellyfish migrate across the lake in huge swarms in pursuit of the sun. Every morning they travel East with the solar rays, stopping around noon to bask, and then returning West in the afternoon.
With hardly any predators in the lake, the Golden jellyfish dominate it, numbering in the millions and commonly concentrating themselves in the prime the most radiant area of the lake as the sun arcs across the sky. As the jellies have very little sting left, and are in such concentrations, the result is a magical opportunity to strap on a snorkel and dive into the swarm.
Well, at least this is the story you are told, before given the green light to dive into a lake full of jellies. Then they also tell you about the toxic layer of hydrogen sulfide which hangs at about 15 meters below the surface. It is a result of bacterial breakdown of organic materials as they fall into the oxygen deprived depths of the lake. It is very poisonous and seeps into the skin, so when you see the water turning hazy orange, do not dive any deeper.
However, for those willing to take a shallow plunge, the reward is spectacular. The sun illuminates the jellies, causing them to radiate golden light through the emerald green lagoon. As you dive through them, it feels like gliding through a million stars in the night sky, some gently brushing across your mask, and along your skin, pulsating on their path towards the bright spot of sun on the lake. They seem to be an undefinable wonder, fluid like the water around them, living from the sun as a plant, yet also gobbling up the occasional plankton with their truncated tendrils like a carnivorous beast.
While this place is a paradigm of evolution, it seems beyond the laws of science. Set deep in a limestone valley, surrounded by sheer cliffs covered in dense foliage, it feels like a secret sheltered cove one might find in The Chronicles of Narnia, or an ancient seafarer’s tales about a mermaid’s oasis. Something that might only occur in the middle of the Pacific Ocean, and something worth traversing the ocean to experience.