- Rising water temperatures have caused major bleaching events, resulting in widespread coral mortality in the Gulf of Mannar.
- Annual studies suggest that live coral cover has declined from 37% in 2005 to 27.3% in 2021.
About corals
- Corals are made up of genetically similar organisms known as polyps.
- These polyps have microscopic algae known as zooxanthellae that live in their tissues in a mutualistic interaction.
- The coral supplies the zooxanthellae with the chemicals required for photosynthesis.
- Zooxanthellae provide the coral with organic photosynthetic products such as carbohydrates, which the coral polyps need to synthesise their calcium carbonate skeletons.
- Corals are marine invertebrates or animals that do not have spines.
- They are the planet’s largest living structures.
- Each coral is referred to as a polyp, and hundreds of such polyps dwell together to create a colony, which expands as polyps reproduce and make copies of themselves.
- Coral reefs are often known as the “rainforests of the seas”.
Types of Coral
There are two types of corals: soft corals and hard corals.
- Hard corals take calcium carbonate from seawater to form hard, white exoskeletons. Hard corals are essentially the engineers of reef ecosystems, and quantifying the extent of hard coral is a commonly accepted indicator for assessing coral reef health.
- Soft corals cling to such skeletons as well as older skeletons formed by their ancestors. Soft corals add their own skeletons to the hard structure throughout time. These developing, replicating structures eventually form coral reefs.
Conditions required for corals to flourish
- Extensive submerged platforms for coral polyp colony production (no deeper than 90 metres below sea level).
- The mean yearly temperature is high, ranging from 20-21 degrees Celsius.
- Clean sediment-free water because murky or turbid water jams the mouths of coral polyps, causing them to die.
- Oceanic salinity ranges between 27 and 30 ppt.
- Ocean currents and waves provide nourishment for the polyps.
How does coral bleach?
- When subjected to situations such as heat stress, pollution, or high ocean acidity, zooxanthellae produce reactive oxygen species that are harmful to corals.
- So the corals kick out the color-giving algae from their polyps, revealing their pale white exoskeleton and causing coral hunger because corals cannot create their own nourishment.
- Severe bleaching and persistent stress in the external environment can cause coral death.
Reasons for the decline.
- Climate variability: Predicted coral bleaching episodes threaten the Gulf of Mannar’s already fragile environment. The IPCC expects a 70-90% decrease in worldwide coral reefs when temperatures rise by 1.5°C.
- water acidification: Increased acidity in the water caused by carbon dioxide absorption exacerbates coral stress and impairs their capacity to calcify.
Source: https://www.thehindu.com/news/national/tamil-nadu/share-of-live-corals-in-gulf-of-mannar-dropped-from-37-in-2005-to-273-in-2021-shows-study/article67900338.ece#:~:text=The%20average%20live%20coral%20cover,Environment%2C%20Climate%20Change%20and%20Forests.