十万个为什么·科学阅读30篇（2）

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珊瑚礁如何在没有骨骼或外壳的情况下建造巨大结构？

Coral reefs are built by tiny animals called polyps that live in colonies underwater.
Each polyp secretes a hard external skeleton made of calcium carbonate from seawater minerals.
Over centuries, generations of polyps add layer upon layer, forming massive limestone frameworks.
Algae living inside coral tissues provide energy through photosynthesis, fueling this growth process.
Water temperature, light, and low nutrient levels must stay within narrow ranges for reefs to thrive.
When stressed by warming or pollution, corals expel their algae and bleach, halting construction.
Reef growth rates vary from 0.3 to 10 centimeters per year depending on species and conditions.
Some reefs, like Australia’s Great Barrier Reef, are over 20 million years old and span 2,300 kilometers.
Unlike shells or bones, coral skeletons are not part of the animal’s body but external deposits.
This collective, slow-building strategy makes reefs the largest biological structures visible from space.