From dawn until dusk, nearly 13 million golden jellyfish (Mastigias sp.) travel from one end of the lake to the other, then back again in a daily spectacle that most of us have only seen in Finding Nemo. Why? They’re following the Sun. The golden jellyfish in these lakes have developed a symbiotic relationship with a type of zooplankton known as zooxanthellae. These algae-like critters live inside the jellyfish’s tissues and photosynthesize sunlight into energy that the jellyfish can use. So every day, starting bright and early, the swarms of jellyfish head east from the western edge of the lake to catch the first rays of sunlight, then track its arc all the way westward again. There, just beyond the shadows cast by the trees, they settle in for the night and wait for day to break once again.
Interestingly, there’s another factor in this migration, one which might have caused it in the first place. The shores of the lake are packed with white sea anemones that will happily snag a passing jellyfish, but these immobile creatures only grow in the shade. If the jellyfish stay in the light, they’re safe, but straying too close to the shadows virtually ensures a quick, brutal end. --
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