How does a coral reef grow?
Photo by Jenny Huang
How does a coral reef grow?
Corals are among Earth’s great architects. The reefs they build are sometimes so vast they can be seen from outer space.
A reef begins when coral larvae settle on the ocean floor. They multiply and mature into coral polyps – tiny anemone-like creatures with stinging tentacles. As the polyps grow, they extract calcium carbonate from seawater, which they secrete as tiny skeletal cups. The large masses of corals in reefs are actually colonies of polyps whose external skeletons are fused together.
In and around the caverns and crevices of a coral reef, other sea creatures take up residence – and together they maintain the health of the reef. Sponges purify the water, and feeding fish act as gardeners – they tend beds of algae and cut back overgrowths of marine plants. Like all big cities, coral reefs have a diverse population. A greater variety of plants and animals live in and around coral reefs than in any other ocean habitat.
You typically find coral reefs about thirty degrees north and south of Earth’s equator. That’s because the corals need warm, clear water that constantly circulates. The sun has to penetrate the water, so tiny algae that live inside the tissue of coral polyps can photosynthesize and make oxygen.
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