地理漫步·世界地理英语30篇（1）
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Jellyfish Lake in Palau and Evolutionary Isolation
帕劳水母湖与进化隔离
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Jellyfish Lake is a marine sinkhole in Palau’s Rock Islands, isolated from the ocean for over 12,000 years by a limestone barrier.
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Two jellyfish species—Mastigias papua etpisoni and Aurelia sp.—evolved stinger reduction due to absence of predators.
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Daily horizontal migration follows sunlight, as symbiotic zooxanthellae require consistent photosynthesis for energy production.
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The lake’s stratified water column features an anoxic, hydrogen sulfide–rich layer below 15 meters that prevents vertical mixing.
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Tourism restrictions limit daily visitors to protect microbial communities and prevent sunscreen-induced algal die-offs.
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Genetic studies show the lake’s jellyfish diverged significantly from oceanic relatives, confirming reproductive isolation.
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Oxygen depletion in deeper layers results from bacterial decomposition of organic matter trapped under the thermocline.
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Seasonal wind shifts occasionally mix surface and deep waters, causing brief jellyfish mortality events followed by population recovery.
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Lake salinity remains slightly lower than seawater due to freshwater seepage through porous limestone fractures.
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Researchers treat the lake as a natural laboratory for studying adaptation in closed, nutrient-limited marine microcosms.