6 things you need to know about coral bleaching right now

The world’s coral reefs are facing “unprecedented global bleaching” according to leading scientists. Earlier this year it was revealed that parts of the Great Barrier Reef had suffered the worst bleaching on record and there are ongoing concerns that the world’s coral reefs are still under threat.

The National Oceanographic and Atmospheric Administration (NOAA) warned this week (June 21) that forecasts show warm ocean temperatures are expected to continue to cause bleaching in the northern hemisphere.

In a statement, NOAA said: "This third global coral bleaching event that began in mid-2014 is ongoing. Global warming, coupled with an intense El Niño continues to make this the longest and most widespread coral bleaching event on record."

With so much concern over coral we explain what coral bleaching is and what it means for the future of the world’s reefs.

What is coral bleaching?

Coral bleaching occurs when the symbiotic relationship between coral and tiny marine algae (zooxanthellae) that live inside corals’ tissues breaks down. The coral expels the living algae, which gives the coral much of its colour and up to 90% of the energy required for it to grow and reproduce. Without the zooxanthellae the coral’s white skeleton is revealed leading to the term “coral bleaching”.

The biggest cause of coral bleaching is a rise in sea temperatures, considered to be one of the biggest threats to the world's oceans. In the case of the Great Barrier Reef it is thought that the combination of global warming and the El Niño weather phenomenon has created the increase.

According to the Australian government’s Great Barrier Reef Authority an increase of only 1ºC over a four-week period can trigger bleaching. If this temperature increase persists for more than eight weeks then corals will start to die.

There are also other factors that can lead to bleaching such as especially bright sunlight, disease, change in salinity and pollution.

Without the zooxanthellae most corals struggle to feed themselves and therefore die. If conditions return to normal it is possible that they can get back their zooxanthellae and regain their colour. However, any amount of bleaching is still likely to impact their growth, reproduction and leave them with increased susceptibility to disease.

Coral bleaching also has a long-term negative impact as reefs tend to take decades to fully recover. This in turn leads to fewer habitats for marine life and less natural protection for shorelines.

The main concern about the current crisis is that it is has been occurring for so long and is so widespread. It is thought that coral in nearly every major reef region has already experienced coral bleaching including areas in the Great Barrier Reef, Maldives, Caribbean, Hawaii and the Pacific Islands.

John Tanzer, director of WWF’s global marine programme said: “I have been working to conserve coral reefs for decades and I have never seen anything like this global bleaching disaster. Coral reefs have been struggling to cope with pollution and overfishing, and now with the impacts of climate change escalating rapidly, their future is dependent on urgent global action.”

The bleaching is already the longest in recorded history and it had previously been hoped that it would end by the middle of this year. However, NOAA’s most recent forecasts suggest that it could now continue until the end of 2016.

There are many conservation groups and world wide organisations that are trying to step in to save the world’s coral reefs. Scientists are also working on incredible new ways to save coral. However, the best way coral can be protected is by reducing climate change. The WWF argues that sea temperature increase needs to be limited to less than 2°C by the end of this century in order for reefs to survive for future generations to enjoy.

Areas under threat are still keen to encourage sustainable tourism as it can help to fund vital scientific works to protect coral. Tourism groups in Australia have reiterated that you  should not be put off visiting the Great Barrier Reef. Speaking at a conference in May the Great Barrier Reef Marine Park Authority confirmed that “superyachts cruising the Great Barrier Reef are not in any way causing coral bleaching”.