The Agatti Reef is experiencing unprecedented mass coral bleaching.
Why in the news?
Extreme heatwaves along the Indian coast, coupled with marine heatwaves, have triggered Mass Coral Bleaching events in the Lakshadweep Sea.
Heatwaves Toll on Lakshadweep’s Coral:
Researchers from the ICAR-Central Marine Fisheries Research Institute (CMFRI) conducted surveys across various Lakshadweep Islands.
The Degree Heating Week (DHW) indicator in Lakshadweep has soared above 4 °C-weeks, as per the National Oceanic and Atmospheric Administration (NOAA).
This elevation in DHW levels poses a substantial risk of coral bleaching, posing a severe threat to the region’s marine ecosystems.
Should DHW surpass 12 °C-weeks, it could trigger an unprecedented biodiversity crisis, leading to multispecies mortality.
Prolonged marine heatwavessince October 2023 have inflicted substantial stress on the coral reefs, exacerbating bleaching phenomena.
A marine heatwave is characterized by seawater temperatures exceeding a seasonally-varying threshold (often the 90th percentile) for at least 5 consecutive days.
Degree Heating Week (DHW) indicator: It is a measurement used to assess the accumulated thermal stress that corals experience over an extended period, which can lead to coral bleaching. This indicator is expressed in °C-weeks, reflecting the exposure of coral reefs to elevated sea surface temperatures.
Lakshadweep’s Coral Treasure: Agatti Reef
Agatti Island is part of the Lakshadweep archipelago, situated in the Arabian Sea.
The island is surrounded by extensive coral reefs, making it a popular destination for snorkeling and diving enthusiasts.
The coral reefs around Agatti Island are composed of various coral species, including branching corals like Acropora, table corals like Acropora Hyacinthus, and massive corals like Porites.
These corals form intricate reef structures that provide habitat and food for numerous marine organisms.
What causes Coral Bleaching?
When exposed to conditions like heat stress, pollution, or high levels of ocean acidity, the zooxanthellae start producing reactive oxygen species not beneficial to the corals.
So, the corals kick out the colour-giving algae from their polyps, exposing their pale white exoskeleton and leading to coral starvation as corals cannot produce their own food.
Severe bleaching and prolonged stress in the external environment can lead to coral death.
Back2Basics: Corals
Coral 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 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 grow 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:
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.
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 degree 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?
Andaman and Nicobar Islands
Gulf of Kachchh
Gulf of Mannar
Sunderbans
Select the correct answer using the code given below:
