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Coral reefs face bleaching events on a global scale

A bleached field of corals A bleached field of corals Ethan Daniels
25 Feb
Increasingly warm ocean temperatures are leading to coral bleaching on a global scale for only the third time in recorded history, and for the first time not during an El Niño period

A new report, released by the National Oceanic and Atmospheric Administration (NOAA), has warned that the severe levels of coral bleaching witnessed in 2014 are likely to continue, or even to worsen, across 2015. Increasingly warm temperatures in the tropical Pacific and Indian Oceans are continuing to rise – according to the NOAA’s newly updated forecast in its Coral Reef Watch, a weekly analysis that forecasts the potential for coral bleaching up to four months in advance.

‘The new outlook gives us greater confidence in what it shows for future coral bleaching and it comes at an important time,’ said Mark Eakin, NOAA Coral Reef Watch coordinator. ‘The outlook shows a pattern over the next four months that is similar to what we saw during global coral bleaching events in 1998 and 2010. We’re really concerned that 2015 may bring the third global coral bleaching event.’

ocean-temp-maps-WEBNOAA Coral Reef Watch’s newly-released four-month bleaching outlook indicates the greatest threat for coral bleaching through May 2015 is in the western Pacific and Indian Oceans in areas such American Samoa, Samoa, Western Australia, and Indonesia. Image: NOAA

The latest forecast shows that the greatest threat for coral bleaching through May 2015 is in the western South Pacific and Indian Oceans.

In the Pacific, thermal stress has already reached levels that cause bleaching in the nations of Nauru, Kiribati, and the Solomon Islands, and is expected to spread to Tuvalu, Samoa, and American Samoa in the next few months. In the Indian Ocean, thermal stress may reach levels that cause bleaching around Madagascar, Mauritius, Seychelles, and parts of Indonesia and western Australia.

shutterstock 76351582Bleached coral on a coral reef. Image: Jon Milnes

The map shows a significant chance that almost all of the southern hemisphere’s coral reefs will experience some level of stress. There has already been some evidence of bleaching in the shallow reefs of American Samoa, according to NOAA scientists, and some predictions that there will be some in the northern hemisphere too as the seasons change – although the models are not able to accurately predict that far.

Under normal circumstances, the analysis would have shown no bleaching as the world is currently not under an El Niño event – a natural phenomenon that raises ocean temperatures. That those temperatures have risen implies that the warming oceans have been caused by climate change. Eakin, speaking to The Guardian, warned that ‘the amount of heat that has been absorbed in the oceans and the warming that has gone on has resulted in the oceans being primed to reach levels that can cause coral bleaching even without big El Niño events’.

UNC professor John Bruno, speaking to CBS News, echoed these sentiments and expressed concern for the future if coral bleaching events started to be seen on a more regular basis: ‘All those places that have recovered will be right back where they were. The concern with global warming is that if we start seeing bleaching events every three years or every five years we won’t start to see any recovery.’

shutterstock 31027972Bleached coral in Venezuela. Image: Tubuceo

‘Climate change and its impacts, which can include bleaching, are some of the most pressing global threats to coral reef ecosystems today,’ said Jennifer Koss, acting program manager for NOAA’s Coral Reef Conservation Program. ‘This suite of products is vital to help scientists, coral reef managers, and decision makers in the U.S. and around the globe prepare for bleaching events.’

‘In the coming months we will be watching to see if the model predicts conditions that can cause bleaching in Southeast Asia and the Coral Triangle region around mid-2015,’ said Eakin. The results will be used as an indicator to see how reliable the new system is and where it can be improved upon.

shutterstock 136653914A Pacific coral that has bleached due to higher than normal sea surface temperatures. Image: Ethan Daniels

This new forecasting tool could be of vital importance in the struggle to combat coral bleaching events. The increasing accuracy of the four-month prediction can give reef managers time to prepare for the event as best they can – utilizing early measures and assessing how best to protect the reefs under their jurisdiction.

However, there is some evidence that the situation may not be as steadfastly bleak as they appear in this report, with some coral reefs showing that they had not suffered from any particularly atypical events in the recent past. The Great Barrier Reef Marine Parks Authority (GBRMPA), for instance, stated in its recent report analysing the reef’s condition that it had seen no major coral bleaching events over the summer, and although it had witnessed some El Niño-esque conditions in late 2014, January 2015 had seen levels return to normal. According to its own prediction, there will be ‘little significant change [expected to those levels] over the coming summer months’. The Director of Reefs for the GBRMPA has also previously stated his opposition to clear-cut statements of doom when it comes to considering coral bleaching, stating that prognostication is premature as he just ‘doesn’t think we know [enough] at this stage’ to have a definitive answer either way.


coralbleaching-large-infographic-WEBInfographic of Coral Bleaching. Image: NOAA
Coral bleaching occurs when corals are stressed by alterations to their living conditions – temperature, light, nutrients, etc. – and so then expel the symbiotic algae living in their tissues, causing them to ‘bleach’ by turning white or pale. While not always fatal, bleaching makes coral far less likely to survive as, without the algae, the coral loses its major food source and is more susceptible to disease.

Not all coral bleaching events occur due to warming water. In January 2010, the water temperature in Florida Keys dropped 12.06 degrees Fahrenheit lower than usual, causing a coral bleaching event that resulted in some coral dying. Scientists are currently attempting to ascertain whether higher or lower fluctuations in temperature have a greater effect on the coral.

Coral bleaching can have detrimental effects both in environmental terms (it supports more species than any other marine environment  – including 4,000 fish species – many of whom would struggle to adapt to other environments) and economic terms (coral has an estimated global monetary worth of £240billion, and sustains many coastal communities that rely on it for their survival, such as through tourism, diving and fishing).

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