地理漫步·世界地理英语30篇（1）

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帕劳水母湖与进化隔离

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