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coral bleaching

The Great Barrier reef bleaches again

The Great Barrier Reef just underwent a third mass bleaching event in five years.The event was the third such mass bleaching instance in five years, perilously close to an almost annual cycle.

The Intergovernmental Panel on Climate Change (IPCC) was categorical in stating last year that even if we manage to limit global temperature rise to 1.5 degrees Celsius , up to 90% of the coral reefs will die. Right now, the world is on course to warming by 3 degrees Celsius or more.

Coral reefs and Climate Change

  • Coral reefs harbour the highest biodiversity of any ecosystem globally and directly support over 500 million peopleworldwide, mostly in poor countries.
  • They are among the most threatened ecosystems on Earth, largely due to unprecedented global warming and climate changes, combined with growing local pressures.
  • Over the last three years, reefs around the world have suffered from mass coral bleaching events as a result of the increase in global surface temperature caused by anthropogenic greenhouse gas emissions.
  • According to UNESCO, the coral reefs in all 29 reef-containing World Heritage sites would cease to exist by the end of this century if we continue to emit greenhouse gases under a business-as-usual scenario.
  • Limiting global average temperature to well below 2°C above pre-industrial levelsin line with the Paris Agreement provides the only chance for the survival of coral reefs globally.
  • Not only does the loss of coral reefs upset the balance of life in the ocean (reefs occupy less than .01% of the global ocean but they support 25% of the global ocean ecosystem), it also indicates that an increasingly hot ocean will unleash more devastating storm surges and cyclones.
  • The high acidity of the ocean indicates a loss of oxygen in the top 1,000m, and this is a massive threat to fish stocks.
  • This frequency of bleaching, according to experts, means two things. One, we are either close to passing or have already passed a particular threshold of ocean warming due to climate change. Two, the Great Barrier Reef event signifies another global round of coral bleaching events.

What are the threats to Coral Reefs?

What is Coral Reef Bleaching?

Coral reefs are colonies of individual animals called polyps, which are related to sea anemones. The polyps, which have tentacles to feed on plankton at night, play host to zooxanthellae, symbiotic algae that live within their tissues and give the coral its color. The coral provides CO2 and waste products that the algae need for photosynthesis. In turn, the algae nourish the coral with oxygen and the organic products of photosynthesis. The coral uses these compounds to synthesize calcium carbonate (limestone) with which it constructs its skeleton—the coral reef.

The symbiotic relationship between corals and zooxanthellae can only exist within the narrow band of environmental conditions found in tropical and subtropical waters. The water must be clear and shallow so that the light algae need for photosynthesis can penetrate, and water temperatures must ideally remain between 23˚ and 29˚ C

Warmer water temperatures can result in coral bleaching. When water is too warm, corals will expel the algae (zooxanthellae) living in their tissues causing the coral to turn completely white. This is called coral bleaching. When a coral bleaches, it is not dead. Corals can survive a bleaching event, but they are under more stress and are subject to mortality.

  • Anthropogenic greenhouse gas emissions have caused an increase in global surface temperature of approximately 1°C since pre-industrial times. This has led to unprecedented mass coral bleaching events which – combined with growing local pressures – have made coral reefs one of the most threatened ecosystems on Earth. When conditions such as the temperature change, corals expel the symbiotic algae living in their tissues, responsible for their colour.
  • A spike of 1–2°C in ocean temperatures sustained over several weeks can lead to bleaching, turning corals white. If corals are bleached for prolonged periods, they eventually die. Coral bleaching events often lead to the death of large amounts of corals.
  • Reefs around the world have suffered from mass bleaching events for three consecutive years. Iconic reefs such as the Great Barrier Reef in Australia and the Northwestern Hawaiian Islands in the United States have all experienced their worst bleaching on record with devastating effects. The bleaching of the Great Barrier Reef in 2016 and 2017, for instance, killed around 50% of its corals.
  • The first global scientific assessmentof climate change impacts on World Heritage coral reefs, published in 2017 by UNESCO, predicts that the coral reefs in all 29 reef-containing World Heritage sites would cease to exist as functioning coral reef ecosystems by the end of this century if humans continue to emit greenhouse gases under a business-as-usual scenario.

Consequences of Coral Reef Bleaching:

  • Coral reefs harbour the highest biodiversity of any ecosystem globally. Coral reefs, the “rainforests of the sea,” are some of the most biodiverse and productive ecosystems on earth. Despite covering less than 0.1% of the ocean floor, reefs host more than one quarter of all marine fish species, in addition to many other marine animals. Additionally, reefs provide a wide variety of ecosystem services such as subsistence food, protection from flooding and sustaining the fishing and tourism industries.
  • Their disappearance will therefore have economic, social and health consequences. Coral reefs are estimated to directly support over 500 million people worldwide, who rely on them for daily subsistence, mostly in poor countries.
  • Coral bleaching impacts peoples’ livelihoods, food security, and safety. Coral reefs are natural barriers that absorb the force of waves and storm surges, keeping coastal communities safe. Without them, we must rely on manmade seawalls that are expensive, less effective, and environmentally damaging to construct.
  • The high acidity of the ocean indicates a loss of oxygen in the top 1,000m, and this is a massive threat to fish stocks.
  • Coral reefs are also key indicators of global ecosystem health. They serve as an early warning sign of what may happen to other less sensitive systems, such as river deltas, if climate change is not urgently addressed. Once the tipping point for the survival of coral reefs is passed, the deterioration of other systems may cascade more quickly and irreversibly.
  • Reef tourism brings in billions of dollars each year and supports thousands of jobs

What can be done?

  • Limiting global average temperature to well below 2°C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5°C, in line with the Paris Agreement on climate change, provides the only chance for the survival of coral reefs globally. If the agreement is fully implemented, we will likely see a decrease in atmospheric carbon concentrations.
  • This will improve conditions for the survival of reefs, and enable other measures to rescue reefs to be successful. Other measures alone, such as addressing local pollution and destructive fishing practices, cannot save coral reefs without stabilised greenhouse gas emissions.
  • Reinforcing commitments to the Paris Agreement must be mirrored in all other global agreements such as the Sustainable Development Goals. SDG 13, for instance, calls for urgent action to combat climate change and its impacts.
  • There also needs to be a transformation of mainstream economic systems and a move towards circular economic practices. These are highlighted in SDG 8 (inclusive and sustainable economic growth) and SDG 12 (sustainable consumption and production patterns). Economic systems need to rapidly move to the low greenhouse gas emission scenario to enable global temperature decrease.
  • A move away from current economic thinking should include the benefits provided by coral reefs, which are currently not taken into account in mainstream business and finance. Therefore, sustaining and restoring coral reefs should be treated as an asset, and long-term investments should be made for their preservation.
  • Investments should also include support for research at the frontiers of biology, such as genetic selection of heat-resistant corals that can withstand rising global temperatures. .

 

Great Barrier Reef:

The 2,300-kilometre (1,430-mile) Great Barrier Reef is the largest coral reef system in the world. The reef is located in the Coral Sea, off the coast of Queensland, Australia. The Great Barrier Reef can be seen from outer space and is the world’s biggest single structure made by living organisms. This reef structure is composed of and built by billions of tiny organisms, known as coral polyps. It supports a wide diversity of life and was selected as a World Heritage Site in 1981.

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