Jellyfish Lakes – Magical Evolution

Jellyfish Lakes jellyfish
Sunrays illuminate a jellyfish

What do you think about swimming in a lake full of jellyfish? For many people even the thought of being in the water with one jellyfish is too much. There is no way they would ever jump into a lake full of them! Or is there? What if we were to tell you that the jellyfish don’t sting? Would this entice you to swim with them?

There are a few places in the world that are home to “jellyfish lakes”. The most famous example is probably in the Republic of Palau. However, Indonesia is also home to a variety of these lakes. They can be found in Sulawesi, Kalimantan, and Raja Ampat. But what exactly is a jellyfish lake? And why don’t the jellyfish sting?

Marine Lakes

There are many marine lakes scattered throughout the world, mainly in Indonesia, Vietnam, and Palau. One of the key things needed to create a marine lake is karst rock. Karst is a type of limestone created from ancient coral reefs. This porous and soft rock is the key to the creation of marine lakes. Eons of biological material broke down the rock to create a depression. These depressions were then filled by the rising ocean levels after the last ice age thousands of years ago. This rising tide of water introduced flora and fauna to the lakes that have evolved in isolation over the intervening years.

Jellyfish Lake in Kakaban, East Kalimantan

Although the lakes are often connected to the ocean via small openings, they typically don’t allow larger organisms to come and go. This has led to a large amount of endemic species being found within these lakes. With over 200 marine lakes known worldwide, they are all different in composition and endemic species.

Why Jellyfish?

Jellyfish are the most dominant species in a special number of these lakes. Having evolved over thousands of years in isolation, they have adapted to isolated living. There are normally two species found within the lakes: the large orange Mastigias and the clear, thin moon jellyfish, although there are a few more as well. The Mastigias are the ones known from famous photographs and documentaries that create large swarms. Although they possess a mild sting, it’s mostly not noticeable to humans. They don’t have active predators in these lakes so no longer require their unique defense mechanism. Unlike their marine cousins that feed on fish, crustaceans, and other marine life, the lake jellyfish use a rather unique way to feed.

Moon jellyfish and Mastigias
Moon Jellyfish and Mastigias

Zooxanthellae and Photosynthesis

As the jellyfish no longer eat larger prey they have evolved a symbiotic relationship with microscopic organisms called zooxanthellae. The zooxanthellae are capable of photosynthesis and provide energy to the jellyfish via sunlight. This is why the jellyfish are found in large groups on the surface of their home lakes, they are following the sun. Throughout the day the jellyfish migrate across the water following the angle of the sun’s rays. At night, the jellies sink below the surface and are able to feed via their small mouths on plankton and other organics in the lake.

Vulnerability of Jellyfish Lakes

Swimming with Jellyfish
Swimming with Mastigias Jellyfish

As the lakes are enclosed systems, they are very vulnerable to damage. Any imbalance in their composition can have tragic consequences. This includes human impacts such as pollution and even tourism. This is why we have to be very careful whenever we visit these unique places. Strong sunscreens, insect repellents, and other chemicals can have long term effects on the lakes. Swimmers also need to be careful when in the water. The jellyfish are extremely fragile and a wayward kick from a fin can maim and kill the jellies. We ask our guests to swim carefully and to avoid using fins when swimming.

Where to Find Jellyfish Lakes in Indonesia?

In Indonesia, the most famous jellyfish lake is on the island of Kakaban in East Kalimantan province. There is also another famous lake in central Sulawesi. On the Samata we often visit the Raja Ampat area where several of these lakes are located. The main ones that we visit are located in the Misool area. Do be aware however that accessing the lakes is not for the feint of heart. We need to climb up and over the karst landscape in order to access the lake. We then need to retrace our steps on the way back. The hike to the lakes is not recommended for those without a decent amount of fitness.

Would you like to see one of these amazing lakes for yourself? Let us know during your cruise on the Samata in the Raja Ampat region. We love visiting the Misool area and the jellyfish lake experience is always a highlight of the trip.

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