At least a quarter of all known marine species are found beneath the ocean's surface, in a vast network of dynamic skeletal-like invertebrates. Coral reefs, which are among the world's most ecologically varied and valuable ecosystems, rely on both hard and soft corals to function. Hundreds of millions of people benefit from them in terms of culture, economics, recreation, and social issues. They provide a supply of medicine as well as protect shorelines from storm damage. And they are dying.
Climate change, declining water quality, overfishing, pollution, and unsustainable coastal development are all putting pressure on coral reefs globally and locally.
“Coral reefs are one of the most sensitive ecosystems globally to the ravages of human activities,” says Gabriel Grimsditch, a marine ecosystems expert with the United Nations Environment Programme (UNEP). "They are particularly vulnerable to climate change and rising ocean temperatures, with mass coral bleaching and mortality events expected to become more common and intense as temperatures rise."
Why do coral reefs die?
When corals are exposed to these stressors, the microscopic symbiotic algae zooxanthellae are expelled from their tissues. Corals become more sensitive to environmental stressors and turn pale or white as a result of this, hence the phrase 'coral bleaching.' Corals must re-absorb the zooxanthellae to recover from bleaching, which is only achievable when environmental stressors are reduced.
“The loss of foundational species like corals that provide important habitat can have devastating consequences and knock-on effects on the thousands of unique and wonderful species that call coral reefs their home,” Grimsditch says.
What is the condition of the world's coral reefs?
According to the UNEP, the International Coral Reef Initiative (ICRI), the Global Coral Reef Monitoring Network (GCRMN), and various international partners' "Status of Coral Reefs of the World 2020" report, 14% of the world's corals were lost between 2009 and 2018, based on a quantitative analysis of a global dataset spanning 1978 to 2019.
Without drastic action to keep global warming to 1.5°C, reefs could lose 70-90% of their living coral by 2050. Even if greenhouse gas emissions are drastically reduced, global ocean temperatures may take decades to stabilise.
However, according to the study, coral reefs are resilient and can return if the marine environment is protected and the correct circumstances are created.
What can we do to help reefs survive?
To secure the survival of coral reefs, decision-makers must take decisive action on climate change. For example, designating coral reefs as a priority ecosystem in the UN Convention on Biological Diversity's Post-2020 Biodiversity Framework would hold governments, companies, and other stakeholders responsible for their protection. Beyond the aims of the Paris Agreement, decision-makers must go above and beyond to ensure the future of coral reefs after the UN Climate Change Conference in Glasgow.
Meanwhile, reef resilience would be enhanced by minimising local anthropogenic stresses through law, education, and other ways. “Climate action and reduction of localised threats must go hand-in-hand if we want coral reefs to survive for future generations to enjoy and benefit from them,” adds Grimsditch.
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