Global Coral Bleaching Events (GCBE)

A GCBE means significant coral bleaching has been confirmed in all the ocean regions where warm-water corals live: the Pacific, Atlantic, and Indian Oceans in both the Northern and Southern Hemispheres.

• Previous Events: Mass coral bleaching recorded in 1998, 2010, and 2014-2017.
• Current Event (GCBE4): Began early 2023, with over 70.7% of the world’s coral reefs impacted by bleaching-level heat stress as of May 23, 2024.

Back2Basics: Corals

• Corals are made up of genetically identical organisms called polyps.
• These polyps have microscopic algae called zooxanthellae living within their tissues in a mutualistic relationship.
• The coral provides the zooxanthellae with the compounds necessary for photosynthesis.
• In return, the zooxanthellae supply the coral with organic products of photosynthesis, like carbohydrates, which are utilized by the coral polyps for the synthesis of their calcium carbonate skeletons.
• Corals are marine invertebrates or animals which do not possess a spine.
• They are the largest living structures on the planet.
• Each coral is called a polyp and thousands of such polyps live together to form a colony, which grows when polyps multiply to make copies of themselves.
• Coral reefs are also called the “rainforests of the seas”.

Types of Coral

Corals are of two types — hard corals and soft corals:

1. Hard corals extract calcium carbonate from seawater to build hard, white coral exoskeletons. Hard corals are in a way the engineers of reef ecosystems and measuring the extent of hard coral is a widely-accepted metric for measuring the condition of coral reefs.
2. Soft corals attach themselves to such skeletons and older skeletons built by their ancestors. Soft corals also add their own skeletons to the hard structure over the years. These growing multiplying structures gradually form coral reefs.

Conditions Needed for Corals to Flourish

• Extensive submarine platforms for the formation of colonies by the coral polyps (not more than 90m below sea level).
• High mean annual temperature ranging 20-21 degrees Celsius.
• Clean sediment-free water because muddy water or turbid water clogs the mouths of coral polyps resulting into their death.
• Oceanic salinity ranging between 27-30 ppt.
• Ocean currents and waves, as they bring food supply for the polyps.

PYQ:

2014: Which of the following have coral reefs?

1. Andaman and Nicobar Islands
2. Gulf of Kachchh
3. Gulf of Mannar
4. Sunderbans

Select the correct answer using the code given below:

(a) 1, 2 and 3 only

(b) 2 and 4 only

(c) 1 and 3 only

(d) 1, 2, 3 and 4