NOAA’s Coral Reef Watch (CRW) and International Coral Reef Initiative (ICRI) confirm 4th global mass coral bleaching event

Posted 17 Apr 2024

Updated 22 Apr 2024

2 min read

Mass bleaching of coral reefs, since early 2023, has been confirmed in at least 53 countries, territories, and local economies including Australia’s Great Barrier Reef.
- It is second such event in the past 10 years with earlier event lasting from 2014 to 2017.
Corals are invertebrate animals belonging to a large group of animals called Cnidaria.
- Generally classified as “hard coral” (reef building corals having rock-like calcareous skeleton) or “soft coral”.
- Coral reefs are formed by polyps of hard corals, which establish symbiotic relationship with microscopic algae, called zooxanthellae, which give them their characteristic colours.
Growth Conditions for Coral Reefs: Warm (23–29°C), salty (32-42 ppt), clear, shallow marine waters with stable temperatures and abundant sunlight.
Significance of reefs: Often called rainforests of the ocean due to high biodiversity and productivity, support around 25% of marine life, minimize storm impact, promote tourism, act as carbon sink etc.
Coral Bleaching: When corals are stressed by changes in conditions such as temperature, light, or nutrients, they expel symbiotic algae, causing them to turn completely white.
- Factors Responsible: Increased Ocean temperature due to climate change, runoff and pollution, extreme low tides, Ocean acidification etc.

Global: ICRI, Global Fund for Coral Reefs, Global Coral Reef Monitoring Network (GCRMN), Coral Triangle Initiative (CTI), etc.
- Coral Triangle is a marine area located in the western Pacific Ocean. It includes the waters of Indonesia, Malaysia, Philippines, Papua New Guinea, Timor Leste and Solomon Islands.
India: Marine Protected Areas (MPAs), Integrated Coastal Zone Management (ICZM) and coral restoration through Biorock technology, etc.

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