World’s northernmost coral reef bleached

Headline : World’s northernmost coral reef bleached

Details :

Bleaching in Japanese waters:
  • Researchers found that bleaching has damaged the world’s northernmost coral reef off the coast of Tsushima island in Japan.
  • This lies in the temperate zone, near the Kyushu islands.
  • Earlier, there was large-scale coral bleaching in Japan’s subtropical Okinawa chain of islands last summer.
  • In response, coral in Okinawa were taking refuge in waters with lower temperatures, expanding their habitat range to (waters off) Kyushu, Shikoku and Honshu.
  • But now coral in refuges are also threatened, and the situation is serious.
High ocean temperatures:
  • It is the latest example of a global phenomenon that scientists have attributed to high ocean temperatures.
  • Since 2015, all tropical coral reefs have seen above-normal temperatures, and more than 70 percent experienced prolonged high temperatures that can cause bleaching.
Importance of corals:
  • Healthy coral reefs protect shores from storms and offer habitats for fish and other marine life, including ecologically and economically important species.
Coral Bleaching:
  • Corals are in a symbiotic relationship with zooxanthellae (algae) that grow inside of them.
  • Algae are vital to the coral. Corals use the organic products of photosynthesis produced by algae to help it grow. The algae also gives the corals their vibrant colours.
  • Coral bleaching occurs when corals are stressed by changes in conditions such as temperature, light, or nutrients.
  • When this happens, the zooxanthellae leave the corals’ bodies.
  • This changes the color of corals to white (as color of coral are due to algea) and can also in effect starve them of nutrients.
  • The loss of algae makes the host vulnerable to disease and can lead to their death.
After bleaching:
  • However, coral can recover if the water temperature drops and the algae are able to re-colonise them.
  • While coral can recover from mild bleaching, severe or long-term episodes are often lethal.
  • After coral dies, reefs quickly degrade and the structures that coral build erode.
Section : Environment & Ecology