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World has lost 14% of its coral reefs to bleaching from global warming

Increasing sea temperatures are pushing the world’s fragile coral reefs to the brink because of mass coral bleaching events caused by global warming.

Between 2009 and 2018, 14% of coral was wiped out, which equates to about 11 700km2 — more than all the living coral in Australia — according to a new UN Environment Programme-backed report on the health of the world’s coral reefs.

Experts from the Global Coral Reef Monitoring Network collected data from more than 300 scientists from 73 countries, including South Africa, over a span of 40 years, including two-million individual observations, for the report, the largest analysis of coral reef health ever undertaken. 

Coral reefs cover just 0.2% of the sea floor but support a quarter of marine species, harbouring the highest biodiversity of any of the world’s ecosystems. If they disappear, the report warns, other marine realms will follow. 

Coral reefs underpin the safety, coastal protection, wellbeing, food and economic security of hundreds of millions of people. The value of the goods and services coral reefs provide is estimated at $2.7-trillion a year, including $36-billion in coral reef tourism.

But coral reefs are under “relentless stress” from warming caused by climate change, coupled with local pressures such as overfishing, unsustainable coastal development and declining water quality.  

Large-scale coral bleaching events caused by elevated sea surface temperatures are the greatest threat to their survival. 

“Almost invariably, sharp declines in coral cover corresponded with rapid increases in sea surface temperatures, indicating their vulnerability to spikes.” 

And as the planet continues to warm, this phenomenon is likely to unfold more often.

“This report is the most comprehensive of its kind on the status and health of the world’s coral reefs and will have important implications for global policy as well as our own domestic policy,” Dr Sean Porter, a coral reef ecologist at the South African Association for Marine Biological Research and an author of the report, told the Mail & Guardian. 

Porter was the South African national coordinator for the report, helping to acquire the monitoring data from various sources, including his own field surveys. 

“South Africa is the 12th-largest greenhouse gas emitter in the world. The only way to mitigate climate change, the most significant threat to coral reefs and much of the terrestrial environment together with habitat destruction, is to urgently move across to renewable forms of energy,” he says.

When waters get too warm, corals become stressed, releasing their colourful symbiotic microalgae, which also gives them their nutrients, turning them skeletal white. Some glow by naturally producing a protective layer of dazzling neon pigments before they bleach. 

“Bleaching can be thought of as the ocean’s version of the canary in the coral mine since it demonstrates coral’s sensitivity to dangerous and deadly conditions,” according to the report.

Since 1978, there has been a 9% decline in the amount of hard coral worldwide, a scientifically based indicator of coral reef health. Between 2010 and 2019, the amount of algae, which signifies stress on reefs, has climbed by 20%.  

This shift from coral to algae-dominated reefs reduces the architectural complexity and structural integrity of these habitats, making them less biodiverse and providing fewer goods and services to humans, according to the report. 

Fortunately for South Africa, Porter says, global warming driven by climate change has not yet caused any major coral bleaching or mortality events on the country’s reefs. 

“Nevertheless, we have seen early warning signs of climate change on our local reefs as we have detected negligible levels (less than 10% of the coral cover) of coral bleaching over the last 25 years, but no mortality. Further north on the continent, the situation is a bit more gloomy as coral reefs have experienced significant levels of bleaching and mortality from global warming since 1998. 

“Most recently, during the 2016 global coral bleaching event, 20% of the Western Indian Ocean’s coral cover died. Seychelles, Madagascar, Kenya and Tanzania were the country’s worst affected.”

All of South Africa’s coral reefs fall within the iSimangaliso Wetland Park World Heritage Site, affording them protection from many of the threats experienced by coral reefs further north, such as dynamite fishing, anchoring, overfishing and coastal development, says Porter.

But there is some concern about the impacts of agricultural chemicals on local coral reefs as well as antimalarial chemicals. “Marine protected areas also cannot protect coral reefs from climate change, but are critical in maintaining their resilience to climate change.”

Relatively little is known about South Africa’s deep water corals, says Porter. “They don’t, however, bleach like shallow water corals do and acquire the majority of their nutrition by filter feeding rather than from symbiotic algae. Nevertheless, they are certainly at risk of being affected by climate change and are generally very slow growing, which makes them particularly vulnerable.” 

Deep water corals are likely to be more affected by ocean acidification resulting from climate change than their shallow water counterparts, “although bottom trawling and marine mining are already impacting deep water corals far more significantly than ocean acidification is”.

Coral reefs are the “backbone” of the marine tourism industry in the Maputaland region of KwaZulu-Natal. “The reefs there support a thriving dive tourism industry in an economically impoverished region with numerous direct and indirect benefits for the local rural communities, including jobs.” 

While the country’s coral reefs have not been comprehensively valued, Porter explains how about 60 000 scuba dives are undertaken on these reefs annually, which contribute a direct value of R75-million per year to the iSimangaliso Wetland Park. 

“Sediment generation and entrapment at Sodwana Bay alone, have been valued at R74.4-million to R89.4-million per year.” 

The rich biodiversity that South Africa’s coral reefs support forms an important component of its natural heritage. Further north, coral reefs become particularly important for natural resource harvesting such as fish and invertebrates, according to Porter.  

“Coral reefs play a very important role in reducing coastal erosion, especially on islands, many of which would not exist if it were not for coral reefs buffering them from the ocean. Most countries in the region also benefit from sustainable ecotourism and recreational fishing that coral reefs provide.” 

There is huge potential for new pharmaceutical discoveries in coral reef animals that may help with cancer and other diseases such as Covid-19, adds Porter.

The outlook for the world’s reefs, in 2021, is bleak, writes Penelope Wensley, the chairperson of the Australian Institute of Marine Science Council, in the report’s foreword.“The need for action to address reef degradation has moved from ‘high priority’ to ‘urgent’ to ‘critical’. Reefs are at a crisis point, linked to the impacts of our changing climate.”

Predictions by the Intergovernmental Panel on Climate Change suggest that with global warming of 1.5℃ coral reefs would decline by 70-90% and be virtually lost with 2℃ of warming. 

But there is hope, according to the report. “Many of the world’s coral reefs remain resilient and can recover if conditions allow, providing hope for the long-term health of coral reefs if immediate steps are taken to stabilise emissions to curb future warming.”

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Sheree Bega
Sheree Bega is an environment reporter at the Mail & Guardian.

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