In an interesting show of evolutionary biology, the M. papua etpisoni is actually a highly adapted Aurelia. About 12000 years ago, the Ice Age caused a large rise in sea level. The seawater spilled over into the Ongeim’l Tketau basin. It was a small, desolate place on a tiny island in the Palauan Island chain.
After the Ice Age ended and the glaciers receded, the jellyfish were closed off from the rest of the world in the newly formed Ongeim’l Tketau or “Jellyfish Lake”. The jellyfish then became more and more endemic to this specific lake in Palau. In the present day, the jellyfish have evolved an extremely mild sting and feed the same way Cassiopeia andromeda does. Here is a link to our post about C. andromeda.
These jellies are so endemic to the lake that they have been named a unique subspecies.
Description:
There are about 8 different species of Mastigas jellyfish. The description is applicable to all of the 8 species, in much the same way as our Aurelia post. Most of them live in the Indo-Pacific ocean, but we will be talking about the etpisoni subspecies.
Because there is no channel to the ocean, the jellies require an internal food supply. In order to get enough food to survive, the jellyfish float upside down and ‘farm’ the zooxanthellae (zoo-O-zan-thella) algae that live in their tentacles. They then eat the waste the algae produce. There is no need for stinging tentacles, so the venom that the jelly produces is so mild that it is practically harmless to humans.
Some of the Ocean species of Masigas have tentacles that sting, but they only use them for self-defense and not predation.
There are also almost no natural jellyfish predators in the Ongeim’l Tketau lake, so the jellyfish are free to roam as they please.
At the peak of their population in 2005, there was an estimated 30 million individual jellyfish in the lake. Due to tourist attraction, the delicate jellyfish were almost extinct in 2017. However, they have been making a steady recovery since then, with an estimated 700,000 individuals in the lake as of now.
Geology & Predators:
The Ongeim’l Tketau lake in Palau is unique in and of itself for a number of reasons. In addition to its layer of stingless jellyfish, there is also a layer of toxic hydrogen sulfide in the bottom portion of the lake.
Hydrogen sulfide is the stuff that causes that rotten egg smell in stagnant water. It is the biproduct of certain bacteria breaking down dead biomatter. The foul odor occurs only sometimes because of the absence of oxygen needing bacteria.
The oxygen needing bacteria die when water at the bottom of the lake (or stagnant water pool) loses all of its oxygen from a lack of plant life or pollution. Though the Ongeim’l Tketau lake is open to the public, its visitors are not allowed to dive below 15 meters (50 ft).
One of the only other organisms in this lake is the Entacmea medusivora or ‘stark white’ anemone species. As the name suggests (medusa = jellyfish, vora = eat), they primarily eat the jellyfish. They are the only natural predator in the lake and can decimate any jellyfish who swim to close.
Amazingly, the jellies are able to detect shadow. This allows them to ‘map’ the walls of the lake. The jellyfish swim in such a way that they will always detect a shadow where the walls of the lake are. This feat allows them to avoid being a snack for the anemones.
As always, we hope that you enjoyed this post. Have a wonderful day.
Cnidology Tonight 