Coral reefs are intricate underwater ecosystems formed by the calcium carbonate skeletons of coral polyps, supporting diverse marine life and often found in warm, clear tropical waters. Examples of coral reefs include the Great Barrier Reef, Rainbow Reef in Fiji, and the Red Sea Coral Reefs. However, these underwater ecosystems, often referred to as the rainforests of the ocean, are currently facing their greatest global threat due to climate change.

Threats Imposed Upon Coral Reefs by Climate Change

• Ocean Warming: Rising sea temperatures, driven by climate change, lead to coral bleaching. Corals rely on symbiotic algae, zooxanthellae, for nutrients and vibrant colours. High sea temperatures cause corals to expel these algae, resulting in bleaching, weakening corals and increasing susceptibility to diseases. o
  • For instance, in 2016 and 2017, the Great Barrier Reef in Australia experienced back-to-back bleaching events due to unusual sea temperatures, affecting two-thirds of the reef and leading to extensive coral mortality.
• Ocean Acidification: Climate change is resulting in ocean acidification, making it more challenging for corals to construct and uphold their structures. This is underscored by a recent study revealing a substantial 14% decline in coral growth within the Great Barrier Reef since 1990, marking the most significant decline in four centuries.
• Sea Level Rise: Due to climate change, rising sea levels pose a threat to these vital ecosystems, leading to increased submergence and sedimentation. This situation reflects historical evidence suggesting that coral reefs may have drowned during the last deglaciation due to adverse environmental conditions associated with sea level rise.
  • Presently, global mean sea level has risen by 97mm (3.8 inches) from 1990 to 2020, emphasizing the ongoing challenges reefs face from rising sea levels.
• Extreme Weather Events and Altered Weather Patterns:
  • Climate change brings about extreme weather events like hurricanes and cyclones, which can physically damage coral reefs by breaking or overturning corals. For instance, the hurricanes Irma and Maria in 2017 caused extensive damage to coral communities in the Caribbean.
  • Additionally, shifts in weather patterns can influence rainfall timing and intensity, causing excess freshwater runoff from heavy rains to introduce pollutants, sediments, and nutrients into coastal waters. This poor water quality can further harm coral reefs. For example, the Indian Ocean’s Chagos Archipelago hasseen shifts in weather patterns, leading to an increase in coral bleaching events.
• Altered Ocean Currents: Climate change can disrupt ocean currents, potentially affecting the distribution of coral larvae. For example, the Red Sea has experienced alterations in its circulation patterns, affecting the transportation of nutrients and larvae, which can impact the health and diversity of its coral reefs.
• Disease Outbreaks: Elevated sea temperatures and stress weaken coral colonies, rendering them more vulnerable to diseases. For instance, in the Dampier Strait MPA, various coral diseases, including WS, BrBD, FB, AtN, Bleaching, and Tumor, have been identified, illustrating the multifaceted challenges corals face.
• Reduced Coral Resilience: Multiple stressors resulting from climate change can reduce the overall resilience of coral reefs. For instance, the Hawaiian Islands have faced a combination of threats, including bleaching, ocean acidification, and increased storms, reducing the overall resilience of its coral reefs.

Strategies to Deal with the Threats

• Coral Nurseries: Establish coral nurseries to propagate and grow resilient coral species, as demonstrated by the Coral Restoration Foundation’s successful efforts in the Florida Keys.
• Coral Bleaching Forecasting: Implement real-time monitoring systems like Australia’s Great Barrier Reef Marine Park Authority’s “Coral Bleaching Early Warning System” to predict coral bleaching events and enable timely protective measures.
• Marine Protected Areas (MPAs): Expand and effectively manage MPAs around coral reefs, with proper enforcement of no-take zones, as seen in the success of the Chagos Marine Protected Area in the Indian Ocean.
• Coral Reef Insurance: Explore innovative financial mechanisms like coral reef insurance, as demonstrated by The Nature Conservancy (TNC) and its partners who successfully pioneered the world’s first reef insurance policy designed to mitigate the significant risk of hurricane damage to coral reefs.
• Cool Roofs and Reflective Pavements: Implement urban planning strategies like the “Cool Roofs” program in New York City to reduce heat absorption in coastal areas, helping mitigate the urban heat island effect and reducing stress on nearby reefs.
• Global Emission Reduction: Implement and enforce international agreements and policies, such as the Paris Agreement to significantly reduce greenhouse gas emissions, thereby mitigating ocean warming and acidification.

The severity and complexity of climate change threats to coral reefs are undeniable. Through the implementation of effective strategies and heightened awareness of their pivotal role in marine ecosystems and coastal communities, we can strive for a future where these vibrant underwater landscapes not only endure but flourish in spite of climate challenges.