WHEN jellyfish vanish, it鈥檚 usually cause for celebration. But their disappearance from Jellyfish Lake in Palau, Micronesia, could act as an early warning of severe weather events caused by El Ni帽o and La Ni帽a.
The saltwater lake is normally home to more than 10 million mastigias jellyfish, but during the strong La Ni帽a event of 1998 they vanished. 鈥淭he dive guys came back shocked, saying the jellyfish had just gone,鈥� says Michael Dawson, a biologist from the University of California, Davis.
His team began recording jellyfish numbers, as well as temperature and salt levels in the water. The creatures normally begin life as small polyps before developing into adult jellyfish, but Dawson鈥檚 group noticed that at temperatures above 35 掳C, the jellyfish remain in their polyp state (Biology Letters, DOI: 10.1098/rsbl.2005.0382).
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During La Ni帽a events the lake becomes warmer than this, so when adult jellyfish die, there are no new ones to replace them, says Dawson. When the lake cools, the polyps begin maturing again and the population is restored.
Since El Ni帽o and La Ni帽a are thought to begin in this region, jellyfish numbers could be used to predict weather patterns in the east three or four months ahead of time.
