Context
The start of the fourth global coral bleaching event in 2023-2024 has been confirmed by the National Oceanic and Atmospheric Administration’s (NOAA) Coral Reef Watch (CRW) of the United States and the International Coral Reef Initiative (ICRI).
National Oceanic and Atmospheric Administration’s (NOAA) Coral Reef Watch (CRW)
- It offers the world’s only global early-warning system of coral reef ecosystem environmental changes.
- Function:
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- To remotely monitors conditions that can cause coral bleaching, disease, and death
- To delivers information and early warnings in near real-time
- To use operational climate forecasts to provide outlooks of stressful environmental conditions on coral reefs worldwide.
- It uses remote sensing, modeled, and in situ data to operate a decision support system
International Coral Reef Initiative (ICRI)
- About: It is a global partnership between Nations and organizations striving to preserve coral reefs and related ecosystems around the world.
- Founded: It was founded in 1994 by eight governments, namely Australia, France, Japan, Jamaica, the Philippines, Sweden, the United Kingdom, and the United States of America.
- It was announced at the First Conference of the Parties of the Convention on Biological Diversity in December 1994.
- Membership: ICRI now counts over 100 members including India
- Foundational documents: ICRI adopted a ‘Call to Action’ and a ‘Framework for Action’ as its foundational documents setting the four cornerstones of ICRI: Integrated Management; Science; Capacity Building and Review.
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Global Coral Bleaching Event
- Extent of Bleaching: CRW and ICRI have recorded bleaching of corals in 53 countries, territories and local economies across five different ocean/sea basins between February 2023 and April 2024.
- Affected Region: The Report confirms widespread bleaching across parts of the Indian Ocean, including Tanzania, Mauritius, the Seychelles, Tromelin, Mayotte, and off the western coast of Indonesia.
- Frequency of Events: The earlier event (3rd global bleaching) had lasted from 2014 to 2017 making the present occurrence second such event in the last 10 years.
- Previous events of global bleaching occurred first in 1998, then in 2010, and between 2014-2017.
- Future Projection: Climate models suggest that bleaching events may become an annual occurrence for most reefs somewhere around 2040-2050.
- CRW Declaration: The CRW declares a global mass coral bleaching event only when it records or gets inputs from all ocean basins of coral bleaching.
Coral Bleaching
- Coral bleaching occurs when the coral Polyp expels the marine algae ie. zooxanthellae from its tissue and breaks the symbiotic relation. This results in them loosing their colour and source of nutrients and energy.
- Stress Response: The bleaching event indicates a stress response enabling them to recover, depending on the intensity of heat stress and its duration.
Corals can recover back to their original health if other stressors such as marine pollution and ocean acidification are kept under check and certain adaptation measures taken.
Causes of Coral Bleaching
- Temperature: The corals can survive only in a specific temperature range and global sea surface temperature is rising because of global warming stressing the corals.
- Extensive Marine Heatwaves: During a marine heatwave, temperatures in vast areas of sea and ocean surfaces increase and remain high for elongated periods of time.
- World Meteorological Organization (WMO)’s State of the Global Climate 2023 Report said that 2023 was the hottest on record for the atmosphere and the oceans with nearly one-third of the global ocean gripped by it any day.
- Subaerial Exposure: Low tides, sea level drops and tectonic uplift can result in sudden exposure of coral to the atmosphere. Subaerial exposure often results in bleaching and consequent coral death due to sudden changes in atmospheric conditions.
- El Nino: Ocean Heating and mass coral bleaching are closely tied to the occurrence of El Nino events since 1997, each of these pairs of El Nino years has also witnessed mass bleaching of corals.
- General Ocean Warming: Ocean warming will pose a serious threat to coral reef ecosystems around the planet, as bleaching events will increase in severity, frequency, and magnitude.
- Example: Localised coral bleaching events have also been witnessed in recent La Nina years in the Great Barrier Reef, off the coast of Australia, in 2020 and 2022.
- Sedimentation: Human Activities such as coastal construction and mining can result in high rates of erosion, increasing sediment content in water and disrupting the natural process of photosynthesis.
- Inorganic Nutrients: Increases in inorganic nutrients such as ammonia and nitrate cause zooxanthellae to multiply by 2-3 times which can cause secondary adverse effects such as lower coral resistance and increased disease susceptibility.
About Corals
- Corals are colonial marine invertebrates of the phylum Cnidaria.
- Polyp: An individual coral is known as a polyp. A polyp is a sac-like animal and they excretes an exoskeleton near the base. Polyps form a symbiotic relationship with plant like cells called zooxanthellae (unicellular dinoflagellates).
- Symbiotic Relationship: Coral Polyp can ingest tiny organisms called plankton & other small creatures but still majority of their energy and nutrients they get from the zooxanthellae living within their tissues which also is responsible for giving the corals its color.
- In return corals provide the zooxanthellae with shelter and protection.
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Conditions for Survival:
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- Shallow Water: Corals require sunlight and clear shallow water for their growth. They are found typically in water above 165 feet (50 meters).
- Clear Water: That lets sunlight through. They don’t thrive well when the water is opaque.
- Warm Water: Reef-building corals require warm water conditions to survive. Different corals living in different regions can withstand water temperatures in the range of 20–32° C.
- Pollution-free water: Corals are sensitive to pollution and sediments. Wastewater discharged into the ocean near the reef can contain too many nutrients that cause seaweeds to overgrow the reef
- Salinity: Corals need saltwater (salinity almost 27 ppt) to survive and require a certain balance in the ratio of salt to water. This is why corals don’t live in areas where rivers drain fresh water into the ocean ie. estuaries
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Also Read: The Coral Fort Initiative
April 17, 2024
