Great Barrier Reef suffers third major bleaching event

Part of: GS-III- Environment and Coral reefs (PT-MAINS-PERSONALITY TEST)

The Great Barrier Reef, the world’s largest coral reef ecosystem located in Australia, recently experienced its third major bleaching event in five years.

1. It is considered to be the most widespread coral bleaching event on record, owing to the rise in temperatures due to climate change.
2. The Great Barrier Reef contains the world’s largest collection of coral reefs, with 400 types of coral, 1,500 species of fish and 4,000 types of molluscs.
3. No other World Heritage property contains such biodiversity.
4. It has suffered several mass bleaching events in the past due to warmer than normal ocean temperatures. Researchers are constantly experimenting with new ways to save the Great Barrier Reef.

About coral reef

Coral reefs are among the world’s most diverse ecosystems, with more than 800 species of corals providing habitat and shelter for approximately 25% of global marine life. Coral reefs are also extremely beneficial to humans: They protect coastlines from tropical storms, provide food and income for 1 billion people, and generate $9.6 billion in tourism and recreation each year. But according to the United Nations Environment Programme, coral reefs are endangered and rapidly degrading due to overfishing, bottom trawling, warming temperatures and unsustainable coastal development.

Also, the abundance and diversity of fish serve as an important indicator of overall reef health

Growth conditions for Coral Reefs

1. The temperature of the water should not be below 20°C. The most favourable temperature for the growth of the coral reefs is between 23°C to 25°C. The temperature should not exceed 35°C.
2. Corals can survive only under saline conditions with an average salinity between 27% to 40%.
3. Coral reefs grow better in shallow water having a depth less than 50 m. The depth of the water should not exceed 200m.

Types of Coral Reefs

Coral Reefs are differentiated into three categories based on their shape, nature and mode of occurrence.

1. Fringing Reef: The coral reefs that are found very close to the land and form a shallow lagoon known as Boat Channel are called Fringing Coral Reefs. The Fringing Reefs develop along the islands and the continental margins. They grow from the deep bottom of the sea and have their seaward side sloping steeply into the deep sea. Fringing Reefs are the most commonly found coral reefs among the three. For example Sakau Island in New Hebrides, South Florida Reef.
2. Barrier Reef: Barrier Reefs are considered as the largest, highest and widest reefs among the three coral reefs. They develop off the coast and parallel to the shore as a broken and irregular ring. Being the largest reef among all, they run for 100kms and is several kilometres wide. One example of a Barrier Reef is the Great Barrier Reef of Australia which is 1200 miles long.
3. Atolls: An atoll can be defined as a reef that is roughly circular and surrounds a large central lagoon. This lagoon is mostly deep having a depth of 80-150 metres. The atolls are situated away from the deep sea platforms and are found around an island or on a submarine platform in an elliptical form. For example Fiji Atolls, Suvadivo in Maldives and Funafoothis Atoll of Ellice.

Coral Reefs in India

India has its coastline extending over 7500 kilometres. It is due to the subtropical climatic conditions, there are a very few coral reefs in India. The major coral reefs in India include the Palk Bay, the Gulf of Mannar, the Gulf of Kutch, the Andaman and Nicobar Islands and Lakshadweep Islands. Among all these coral reefs, the Lakshadweep reef is an example of atoll while the rest are all fringing reefs.

Palk Bay

Situated in the south-east coast of India, Palk Bay is separated from the Gulf of Mannar by the Mandapam Peninsula and the Rameshwaram Island and is centered on 9 °17’N and 79° 15′. The one fringing reef in the Palk Bay is 25-30km long, and less than 200m wide lies in the east-west direction of the Pamban channel. This reef has a maximum depth of around 3 m.

The Gulf of Mannar

Situated around a chain of 21 islands, the Gulf of Mannar lies between Tuticorin and Rameswaram at a stretch of 140 km. These 21 islands fall between latitude 8°47′ N and 9° 15′ N and longitude 78° 12′ E and 79° 14’E and form a part of the Mannar Barrier Reef which is 140 km long and 25 km wide.

Andaman and Nicobar Islands

The Andaman and Nicobar Islands fall between 6°-14° N lat and 91 °-94° E longitude. They are situated at the south-eastern part of the Bay of Bengal and consist of 350 islands, of which only 38 are inhabited. These islands extend southward from the Irrawaddy Delta of Burma to the Arakan Yoma Range. All the islands of the Andaman and Nicobar groups are almost fringing reefs.

The Gulf of Kutch

The Gulf of Kutch is situated in the northern part of Saurashtra Peninsula and is located between 22°15′-23°40′ N Latitude and 68°20′-70°40′ East Longitude having an area of about 7350 sq km. These reefs are of fringing type and are about 170 km long and 75 km wide at the mouth which narrows down at a longitude of 72° 20′. Due to the mud deposits on various coral reefs, these coral reefs are in a highly degraded condition.

Lakshadweep Islands

Located between 8°N – 12°3’N latitude and 71 °E- 74°E longitude, the Lakshadweep Islands which lies scattered in the Arabian Sea are situated at about 225 km to 450 km from the Kerala Coast. The islands covering an area of 32 km2 consist of 36 tiny islands, 12 atolls, 3 reefs and 5 submerged banks, with lagoons occupying about 4200 km2.

Due to the warm humid climate of these islands, the temperature of the water varies between 28-31 °C with salinity ranging from 34% – 37%.

Coral Bleaching

The United Nations has reported that:

• • 70% of the Earth's coral reefs are threatened,
  • 20% have been destroyed with no hope for recovery,
  • 24% are under imminent risk of collapse, and
  • an additional 26% are at risk due to longer-term threats.

According to a recent report, if stern measures to bring down the greenhouse gas emission levels are not adopted urgently, then Australia’s Great Barrier Reef might be in danger of coral bleaching as frequently as every two years by 2034. Large scale coral bleaching in 2016 destroyed thousands of square kilometres of the Great Barrier Reef.

Hawaii became the first U.S. state to put curbs on the sale of sunscreens containing oxybenzone and octinoxate, which can cause coral bleaching.

What is Coral Bleaching?

• When corals face stress by changes in conditions such as temperature, light, or nutrients, they expel the symbiotic algae zooxanthellae living in their tissues, causing them to turn completely white. This phenomenon is called coral bleaching.
• The pale white colour is of the translucent tissues of calcium carbonate which are visible due to the loss of pigment producing zooxanthellae.
• Corals can recover if the stress-caused bleaching is not severe.
• Coral bleaching has occurred in the Caribbean, Indian, and Pacific oceans on a regular basis.

Causes of Coral Bleaching?

• Rise in Sea Temperature: Most coral species live in waters close to the warmest temperature they can tolerate i.e., a slight increase in ocean temperature can harm corals. El Nino elevates the sea temperature and destroys coral reefs.
• Ocean Acidification: Due to rise in carbon dioxide levels, oceans absorb more carbon dioxide. This increases the acidity of ocean water and inhibits the corals ability to create calcareous skeletons, which is essential for their survival.
• Solar radiation and ultraviolet radiation: Changes in tropical weather patterns result in less cloud cover and more radiations which induce coral bleaching.
• Infectious Diseases: Penetration of bacterium like vibrio shiloi inhibits photosynthesis of zooxanthellae. These bacteria become more potent with elevated sea temperatures.
• Chemical Pollution: Increased nutrient concentrations affect corals by promoting phytoplankton growth, which in turn supports increased numbers of organisms that compete with coral for space.
• Increased Sedimentation: Land clearing and coastal construction result in high rates of erosion and a higher density of suspended silt particles which can
  • smother corals when particles settle out (sedimentation),
  • reducing light availability (turbidity) and
  • potentially reducing coral photosynthesis and growth.
• Human Induced Threats: Over-fishing, pollution from agricultural and industrial runoff, coral mining, development of industrial areas near coral ecosystems also adversely impact corals.

Consequences

• Changes in coral communities can affect the species that depend on them, such as the fish and invertebrates that rely on live coral for food, shelter. Loss of such marine animals can disturb the entire food chain.
• Declines in genetic and species diversity may occur when corals die as a result of bleaching.
• Healthy coral reefs attract divers and other tourists. Bleached and degraded reefs can discourage tourism, which can affect the local economy.
• Coral bleaching can cause large shifts in fish communities. This can translate into reduced catches for fishers, which in turn impacts food supply and associated economic activities.
• Coral reefs protect coastlines by absorbing constant wave energy from the ocean, thereby protecting people living near the coast from increased storm damage, erosion and flooding.

Way Forward

• Solutions for protecting the future for coral must transcend social, economic and cultural boundaries.
• Halting unplanned coastal development would play a significant role in reversing the decline of reefs in some locations.
• Promoting sustainable fishing and providing opportunities for ecotourism can help conserve corals.
• There is a need to minimise the use of chemically enhanced fertilizers, insecticides, pesticides, and herbicides which are non degradable and harm corals.
• Harmful industrial waste must be treated before being disposed of in bodies of water.
• Water pollution should be avoided wherever possible by not dumping chemicals or oils in water bodies.
• Taking all possible measures to prevent actions that worsen global warming since Climate change is the greatest global threat to coral reef ecosystems.