Third mass bleaching of Great Barrier Reef recorded 
Context: Recently, Australia’s Great Barrier Reef has suffered its most widespread coral bleaching on record.Record sea temperatures caused the third mass bleaching of the 2,300-kilometre reef system in just five years.
Key Findings

• For the first time, severe bleaching has struck all three regions of the Great Barrier Reef — the northern, central and now large parts of the southern sectors.
• The damage came as February brought the highest monthly sea temperatures on the Great Barrier Reef since Australia began keeping records in 1900.

About Bleaching 

• Bleaching occurs when healthy corals become stressed by changes in ocean temperatures, causing them to expel algae living in their tissues which drains them of their vibrant colours.
• Bleaching was first seen on the reef in 1998 — at the time, the hottest year on record — but as temperature records continue to tumble its frequency has increased, giving coral less time to recover.

Context: Scientists have warned that the Great Barrier Reef will face a critical period of heat stress over the coming weeks, following the most widespread coral bleaching the natural world has ever endured.
About the current scenario

• Warming ocean temperatures, a sign of climate change, is associated with the deteriorating health of the Reef. 
• The Great Barrier Reef Marine Park, which spreads across a length of over 2,300 km and is roughly the size of Italy, is home to about 3,000 coral reefs, 600 continental islands, 1,625 type of fish, 133 varieties of shark and rays and 600 types of soft and hard corals.

About Coral bleaching

• According to the National Oceanic and Atmospheric Administration (NOAA), when corals are stressed by changes in conditions such as temperature, light or nutrients, they expel the algae living in their tissue, causing them to turn white, hence bleached.
• Coral bleaching does not mean the corals are dead, but make them vulnerable, hence increasing their mortality. 
• Warm ocean temperatures are one condition that could lead to coral bleaching. For instance, in 2005, the US lost half of its coral reefs in the Caribbean in one year due to a massive bleaching event.
• Even so, NOAA says that not all bleaching events are due to warmer temperatures. In January 2010, cold water temperatures in the Florida Keys caused a coral bleaching event that resulted in some coral deaths.

How does it affect the Great Barrier Reef?

• The Great Barrier Reef, which covers an area of 344,400 sq km makes up roughly 10 per cent of the world’s coral reef ecosystems. Today, the reef is a Marine Park and World Heritage Area and supports a range of activities and contributes over AUD $5.6 billion each year to the Australian economy and is also responsible for creating over 70,000 jobs.
• In the 2019 Outlook Report prepared by the Australian government, it said that climate change was the greatest threat to the Reef. Other threats included coastal development, land-based run-off and direct human use, such as activities like illegal fishing.
• Significantly, coral bleaching events such as the ones that took place in 2016 and 2017 have had severe impacts on the Reef, causing changes in its ecosystem. However, some parts of the reef that escaped the impact of the bleaching and cyclones still remain in good condition, the report said.
• The 2016 bleaching caused by intense heat exposure affected the northern third region of the Reef, while the 2017 bleaching affected the central region.
• As per the latest Reef health update, while sea surface temperatures have remained relatively stable this week (until March 5, 2020), the temperature is still above normal for this time of the year. As of March 3, most of the marine park varies between 0.5 degree-1.5 degree Celsius above normal. In some inshore areas, the temperature is 2.5-3 degrees Celsius warmer.

Ways to maintain the balance between nature and human

• The world needs coral reefs, and decisive action will help ensure that we do not face a future without them.Adequate mitigation and adaptation measures must be put in place to arrest the effects of climate change
• We must devise policies to provide protection to existing carbon sinks such as corals like Reducing greenhouse emissions will be critical here.
• Effectively reducing local stresses to reefs, such as from land-based sources of pollution and overfishing.
• Increasing electricity generation from the renewable sources rather than depend on the artificial removal of carbon dioxide from the atmosphere.
• Conserving water. The less it is used, the less runoff and wastewater that will eventually find its way back into the ocean.
• Educating people about why healthy coral reefs are valuable to the people, fish, plants, and animals that depend on them.