Written by Alex Rose
Jellyfish Lake in Palau is famous. As the name suggests, the creature that makes it so famous is the jellyfish. And not just any jellyfish, but a unique subspecies of the golden jellyfish (Mastigias cf. papua etpisoni) that is found nowhere else in the world. But if you were to go snorkeling in this lake right now, you would find a mysterious absence of this place’s namesake. So where have all the jellyfish gone?
According to scientists, a severe drought coupled with hotter than usual temperatures brought about by a particularly strong El Nino weather pattern are primarily to blame. At the peak of their population, there were about 12 million jellies living in the lake. That number had declined to 600,000 by the beginning of 2016 and there are reports that they are currently almost nonexistent. It appears as though the adult jellyfish have nearly completely died out while at least some juveniles remain. Jellyfish exist as sessile polyps before they turn into the free swimming medusa form that we recognize, and it appears that jellyfish polyps still remain indicating a possibility for the population to rebound when conditions are more favorable. The lack of rain has caused the water to become saltier than ever previously recorded and the warm temperatures have heated the water excessively, both conditions that have been extremely stressful to the lake’s inhabitants.
Other than the channels in the limestone rock deep below the lake, this body of water is land locked and has no supply of fresh sea water. Without ocean water flowing in and bringing nutrients with it, the phytoplankton and plankton the jellyfish consume have less food to fuel their growth, a factor that limits the jellyfish population. While the jellies have photosynthetic capabilities, meaning that they are able to produce their own food from the sun, they still rely on plankton for sustenance. On top of nutrients being in short supply due to the lack of incoming water, it also means that Jellyfish Lake has no fresh supply of jellyfish larvae from anywhere other than within the lake itself, a fact that makes this rapid population decline a bit unsettling.
This same scenario has occurred before and the population rebounded fairly quickly. 1998 is known as another severe El Nino year, and in 1999, Jellyfish Lake experienced the same phenomenon. The jellies nearly disappeared that year, but the population recovered from the initial crash within 18 months. Hopefully the 2016 crash will have a similar outcome, but many people are still worried.
The El Nino Southern Oscillation (ENSO) is not a new pattern, but its severity increases along with temperature. As our climate warms, the extra heat fuels more drastic fluctuations in temperature, rainfall and wind, causing drought in some places and flooding in others. The prolonged heat in certain areas associated with elevated surface temperatures can spell trouble for many places, including Jellyfish Lake. It is reasonable to expect the jelly population to recover over the next few years, but it is also likely that this will happen again and probably with increased frequency as global climate change continues to heat up our planet.