Great Barrier Reef: 93% of reefs hit by coral bleaching

• According to a recently conducted survey on Great Barrier reef, almost 93% of reefs on the Great Barrier Reef have been hit by coral bleaching.
• This is happening due to warmer water temperature which left only 7 % of total reef area without any whitening of great barrier reef.
• On the southern area, damage is less , but on the northern area it is severe and on the eastern coastal side it reaches upto 2,300 kilometre .
• There is a severe coral bleaching event occurring not just in the Great Barrier Reef but throughout many parts of the Pacific.
• Bleaching began in Hawaii late last year and had already affected several Pacific islands.
• New Caledonia, the Coral Sea, the northern half of the Barrier Reef and New South Wales are bleaching severely, and western Australia is quickly catching up
• Bleaching occurs when abnormal environmental conditions, such as warmer sea temperatures, cause corals to expel tiny photosynthetic algae, draining them of their colour.
• Corals can recover if the water temperature drops and the algae are able to recolonise them, but scientists warned last year that the warming effects of a El Nino weather pattern could result in a mass global bleaching event

What is coral bleaching

• Many types of coral have a special symbiotic relationship with a tiny marine algae (zooxanthellae) that live inside corals' tissue and are very efficient food producers that provide up to 90 per cent of the energy corals require to grow and reproduce.
• Coral bleaching occurs when the relationship between the coral host and zooxanthellae, which give coral much of their colour, breaks down. Without the zooxanthellae, the tissue of the coral animal appears transparent and the coral's bright white skeleton is revealed.
• Corals begin to starve once they bleach. While some corals are able to feed themselves, most corals struggle to survive without their zooxanthellae.
• If conditions return to normal, corals can regain their zooxanthellae, return to their normal colour and survive. However, this stress is likely to cause decreased coral growth and reproduction, and increased susceptibility to disease.
• Bleached corals often die if the stress persists. Coral reefs that have high rates of coral death following bleaching can take many years or decades to recover.

What causes coral bleaching

• The main cause of coral bleaching is heat stress resulting from high sea temperatures. Temperature increases of only one degree celsius for only four weeks can trigger bleaching events.
• If these temperatures persist for longer periods (eight weeks or more) corals begin to die. High water temperatures can affect reefs at regional and global scale.
• Other stressors can also cause bleaching, including freshwater inundation (low salinity) and poor water quality from sediment or pollutant run-off.

Coral bleaching and  the Great Barrier Reef

• The Great Barrier Reef has experienced mass coral bleaching events in the past.
• In 1998, there was a global mass bleaching event where 50 per cent of the reefs on the Great Barrier Reef suffered bleaching. During this time, sea temperatures on the Great Barrier Reef were the highest ever recorded.
• Mass bleaching also occurred in 2002, with 60 per cent of reefs were affected. This was the largest coral bleaching event on record. Two periods of hot weather resulted in sea surface temperatures a few degrees centigrade higher than long-term summer maxima.In both events, about five per cent of the Great Barrier Reef's coral reefs were severely damaged.

By: Vishal