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Coral reefs cover less than 1 per cent of the ocean floor, yet they support about a quarter of all known marine species. They also shield coasts from storm waves.

Coral reefs

OceanClimateBiologyScience

The story behind the card

A reef is built by coral polyps, tiny animals related to jellyfish that lay down skeletons of limestone. Most reef corals carry single-celled algae inside their tissue; the algae photosynthesise and pass food to the coral in return for shelter, and they also give it its colour. When the water stays too warm for too long, corals expel the algae and turn white, which is called bleaching; if the heat lasts, they starve and die. A global bleaching event from 2014 to 2017 hit about two-thirds of the world's reefs, and a fourth, from 2023 to 2025, the most severe on record, reached about 84 per cent of reef area.

Türkçe oku
Mercan resifleri okyanus tabanının yüzde 1'inden azını kaplar; buna karşın bilinen deniz türlerinin yaklaşık dörtte biri resiflere bağlı yaşar. Resifler kıyıları fırtına dalgalarından da korur.

Resifleri mercan polipleri kurar: Denizanalarıyla akraba olan ve kireçtaşından iskelet yapan küçük hayvanlar. Resif mercanlarının çoğu, dokularının içinde tek hücreli algler taşır. Algler fotosentez yaparak mercanı besler, karşılığında barınak bulur; mercana rengini de onlar verir. Su uzun süre fazla ısınınca mercanlar algleri dışarı atar ve bembeyaz kalır; buna mercan beyazlaması denir. Sıcaklık sürerse mercanlar açlıktan ölür. 2014–2017 arasındaki küresel beyazlama, dünya resiflerinin yaklaşık üçte ikisini etkiledi. Kayıtlardaki en şiddetli olay olan ve 2023–2025 arasında yaşanan dördüncü küresel beyazlama ise resif alanının yaklaşık yüzde 84'üne ulaştı.

Sources and further reading

Background reading: Coral reef
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