school energy&environment

Bleaching: whitening of coral

“Bleaching” is the term now commonly used to define the “whitening” of corals. In case of environmental stresses (for instance a temperature increase), coral polyps throw out the algae which live in symbiosis with them, the zooxanthellae, that give colour to the corals with their photosynthetic pigment. The consequence of such phenomenon is the coral colony losing its colour, sometimes becoming totally white. When like this, the coral is not dead; as soon as the conditions that caused this phenomenon cease, the algae re-colonise the polyps and the situation gets back as it was before. Otherwise, the coral will die. The main cause of the destruction of the reefs seems to be the increasingly high temperature of the oceans. In 1998, the “bleaching” phenomenon reached catastrophic proportions due to the passage of the Niño (a phenomenon which involves abnormal displacements of water in the oceans) which caused the mean temperature to increase by 2°C, thus making 90% of the coral die in some areas in the Indian Ocean. It is as if all of a sudden a millenary forest caught fire, thus causing an almost irreparable ecological damage. In addition, the damage is not just ecological or biological, reducing biodiversity, but it is also a socio-economic one for all those communities whose survival depends on the reef.