As the world grapples with climate change, coral reefs – vital ecosystems in tropical oceans – are at a breaking point. With nearly half of all tropical coral species now facing extinction, urgent action is needed to prevent an ecological collapse that would affect marine biodiversity and millions of human livelihoods.
The International Union for Conservation of Nature (IUCN) recently announced that 44% of tropical, reef-building coral species are now threatened with extinction. This significant rise from 2008’s 33% underscores the ongoing impact of climate change on marine environments. At COP29 in Azerbaijan, a report detailing these findings was presented, though major leaders from top-polluting countries were implementing effective policies to curb global warming.
Rising Ocean Temperatures and Coral Bleaching
According to the National Oceanic and Atmospheric Administration (NOAA), oceans absorb approximately 90% of the excess heat generated by greenhouse gases like carbon dioxide, making them critical buffers against rapid atmospheric temperature increases. However, this protective role comes at a cost: since 1955, the top 2,000 meters of the ocean have warmed by an estimated 0.6 degrees Celsius. This seemingly small change has resulted in mass coral bleaching events that severely damage these sensitive organisms.
Bleaching occurs when higher temperatures disrupt the symbiotic relationship between corals and the algae (zooxanthellae) that live within them. When corals expel these algae, they lose their color and, more importantly, their primary source of nutrients. Coral reefs, such as Australia’s Great Barrier Reef, have endured five major bleaching events in the past three decades, with the most recent event in 2023 being among the worst on record.
Economic Impact of Coral Reef Decline
Coral reefs play an essential role in global ecosystems and economies, supporting an estimated $375 billion in ecosystem services annually. For instance, they protect coastal communities from storm surges, erosion, and flooding, serving as natural barriers. Additionally, coral reefs support about 25% of all marine species and are crucial to global fisheries, providing sustenance for millions of people, especially in developing countries. The tourism industry also heavily depends on healthy reefs, with some estimates suggesting they generate upwards of $36 billion globally in tourism-related revenue each year.
IUCN Red List: 44% of Coral Species Threatened
The IUCN’s updated Red List of Threatened Species evaluated 892 tropical reef-building coral species and found that 392 of them are now classified as threatened. This assessment includes coral species in the Atlantic, where nearly one in three species faces critical endangerment. Notably, staghorn and elkhorn corals in the Caribbean have been severely impacted, suffering not only from warming waters but also from pollution and hurricanes that ravage these fragile ecosystems. The rate of reef-building coral decline has accelerated since the last IUCN assessment in 2008, with the potential for further species loss without immediate intervention.
Factors Driving Coral Reef Decline
While climate change is the leading cause, other factors also jeopardize coral reefs. Pollution, unsustainable fishing, and agricultural runoff introduce toxins and excess nutrients that disrupt the delicate balance within coral ecosystems. Runoff from fertilizers and pesticides promotes the growth of algae and bacteria that compete with corals for space and resources, further straining their survival. Additionally, ocean acidification – a byproduct of absorbing excess CO₂ – weakens coral skeletons, making them more vulnerable to erosion and breakage.
Ocean Acidification: An Escalating Threat
When CO₂ dissolves in seawater, it forms carbonic acid, which reduces pH levels and affects marine life. Over the past century, ocean pH has decreased by 0.1 units, a seemingly minor shift with significant consequences. The more acidic waters dissolve calcium carbonate, which is essential for corals to build their structures. The IPCC projects that by 2100, the ocean’s pH could drop by an additional 0.3 to 0.4 units, drastically altering marine ecosystems and further jeopardizing coral reefs.
Regional Impacts and High-Risk Areas
The Indo-Pacific region, home to over 75% of the world’s coral reefs, is particularly vulnerable. Here, coral reefs such as those in the Philippines, Indonesia, and Australia face high extinction risks, exacerbated by local pollution and destructive fishing practices. In contrast, cold-water coral species, often found in deeper, darker ocean environments, are still under assessment due to the difficulty of studying them in situ. However, early indications suggest that they are not immune to the broader impacts of climate change and human activities.
In the Atlantic, coral reefs face similarly stark prospects. The PLOS One journal recently published findings indicating that 23 of the Atlantic’s 85 coral species are critically endangered. The Atlantic corals, unlike their Indo-Pacific counterparts, endure additional pressures from more frequent and intense hurricanes, adding physical destruction to the chemical and thermal stressors.
Calls for Action at COP29
IUCN representatives at COP29 urged governments to prioritize coral conservation, stressing that immediate action is needed to reduce emissions from fossil fuels. Grethel Aguilar, the IUCN’s chief, emphasized that coral reefs are more than just beautiful underwater landscapes; they are critical to food security, coastal protection, and carbon storage. The organization called on global leaders to support initiatives focused on restoring coral ecosystems and implementing sustainable management practices.
David Obura, an IUCN coral specialist, warned of the irreversible consequences if policy measures fail to change the current trajectory: “Without relevant decisions from those with the power to change this trajectory, we will see the further loss of reefs and progressive disappearance of coral species at larger and larger scales.”
Can the World’s Reefs Survive Climate Change?
With nearly half of all tropical coral species now facing extinction, coral reefs are in critical need of protection. The current trajectory points to further losses, but coordinated efforts in emissions reduction, policy change, and innovative conservation practices could alter the outcome. As world leaders convene at COP29, the call to action is clear: to save coral reefs, humanity must address the root causes of climate change and implement sustainable solutions to protect these invaluable ecosystems for future generations.
