TAG: GS 3: ECOLOGY AND ENVIRONMENT
THE CONTEXT: The ICAR-Central Marine Fisheries Research Institute (CMFRI) has found that coral reefs in the Lakshadweep Sea have undergone severe bleaching due to prolonged marine heatwaves since October 2023.
EXPLANATION:
The Impact of Rising Sea Temperatures
- The Lakshadweep Sea has been experiencing temperatures consistently exceeding 1 degree Celsius above the norm since October 2023.
- Such thermal stress exacerbates coral bleaching, with Degree Heating Week (DHW) values surpassing 4 degrees Celsius weeks, a threshold indicative of significant bleaching.
- Degree Heating Week (DHW) shows how much heat stress has accumulated in an area over the past 12 weeks (3 months) by adding up any temperature exceeding the bleaching threshold during that period.
- When DHW reaches 4°C-weeks (7.2°F-weeks), significant coral bleaching is likely, especially in more sensitive species.
- When DHW is 8°C-weeks (14.4°F-weeks) or higher, widespread bleaching and mortality from thermal stress may occur.
- This rise in sea temperatures can be attributed to various factors, including global warming and shifts in ocean currents.
- While coral bleaching events have occurred in Lakshadweep previously, the scale of the current crisis is unprecedented.
- The severity of bleaching threatens the long-term health of Lakshadweep’s coral reefs, which are vital for sustaining the islands’ structure and biodiversity.
- Furthermore, coral bleaching affects corals and endangers the livelihoods of coastal communities reliant on fisheries and tourism.
Lakshadweep Sea has been seeing above-average temperatures since Oct 2023
A Wider Trend: Marine Heatwaves in the Indian Ocean
- The phenomenon of marine heatwaves is not unique to Lakshadweep but is part of a broader trend affecting the Indian Ocean.
- Studies have shown a significant increase in marine heat waves across the region, which can be attributed to rapid warming and strong El Niño events.
- These heatwaves have detrimental effects not only on coral reefs but also on other marine habitats, such as seagrass meadows and kelp forests, impacting ecosystem functions and biodiversity.
Coral Reefs: The Lifelines of Oceanic Ecosystems
- Corals, often mistaken as plants or rocks due to their stationary nature, are actually living animals.
- They belong to the phylum Cnidaria and class Anthozoa. These sessile organisms permanently attach themselves to the ocean floor, forming colonies of genetically identical polyps.
- Each polyp has a cylindrical body surrounded by tentacles used for feeding.
- Corals come in two main types: hard corals and soft corals. Hard corals, such as those belonging to the genus Acropora, build the intricate limestone skeletons that form coral reefs, while soft corals lack this rigid structure.
- Coral reefs are diverse underwater ecosystems built by the accumulation and growth of coral colonies over thousands of years.
- They are often referred to as the “rainforests of the sea” due to their extraordinary biodiversity and importance in supporting marine life.
- The Great Barrier Reef in Australia, spanning over 2,000 kilometers, stands as the largest coral reef system globally.
- Coral reefs host a vast array of marine species, including fish, mollusks, sea turtles, and countless others, making them one of the most biologically productive ecosystems on Earth.
Coral Bleaching: A Threatening Phenomenon
- Corals maintain a symbiotic relationship with tiny photosynthetic algae called zooxanthellae, which reside within their tissues.
- These algae provide corals with essential nutrients through photosynthesis while receiving shelter and nutrients in return.
- The symbiotic algae also impart vibrant colours to the corals, contributing to their visual appeal.
- Coral bleaching occurs when corals expel their zooxanthellae due to environmental stressors, such as elevated sea temperatures, pollution, or changes in water chemistry.
- Without the presence of zooxanthellae, corals lose their vibrant colors and appear white or pale. While coral bleaching does not immediately result in coral death, it increases their susceptibility to mortality and reduces their reproductive capacity.
Types of coral reefs in India:
- Fringing reefs
- Fringing reefs evolve and develop near the continent and remain close to the coastline. These reefs are separated from the coastline by small, shallow lagoons. They are the most commonly found reefs in the world.
- Barrier reefs
- Barrier reefs are found offshore on the continental shelf. They usually run parallel to the coastline at some distance. A deep and wide lagoon is located between the coastline and the barrier reef.
- Atolls
- Atolls are formed on mid-oceanic ridges. They are circular or elliptical, surrounded by seas on all four sides, and have shallow waters in the center called lagoons.
- All the three major reef types occur in India. The mainland coast of India has two widely separated areas containing reefs: the Gulf of Kachchh in the northwest, which has some of the most northern reefs in the world, and Palk Bay and the Gulf of Mannar in the southeast.
- In addition to these, there are patches of reef growth on the West Coast, for example, coral reefs at Malvan.
- The Andaman and Nicobar Islands have fringing reefs around many islands, and a long barrier reef (329 km) on the west coast.
- Little is known about these reefs, which may be the most diverse and pristine reefs in India. The Lakshadweep also has extensive reefs but these are also poorly explored.
ICAR-Central Marine Fisheries Research Institute (CMFRI):
- It was established in 1947 under the Ministry of Agriculture and Farmers Welfare in India.
- In 1967, it joined the Indian Council of Agricultural Research (ICAR) family and became a leading tropical marine fisheries research institute globally.
- Its headquarters is in Kochi, Kerala.