How are coral reefs threatened by increasing concentrations of dissolved carbon dioxide in oceans?

Sourav PanNovember 8, 2024

Answered

Increasing concentrations of dissolved carbon dioxide (CO₂) in the oceans pose significant threats to coral reefs, primarily through the process of ocean acidification and its associated effects. Here’s a detailed explanation of how these changes impact coral reefs:

Ocean Acidification

1. Chemical Changes:
   • When CO₂ dissolves in seawater, it reacts with water to form carbonic acid, which then dissociates into bicarbonate and hydrogen ions. This process lowers the pH of the ocean, making it more acidic. Since the start of the Industrial Revolution, ocean pH has dropped from about 8.2 to 8.1, indicating a roughly 30% increase in acidity.
2. Impact on Calcium Carbonate Formation:
   • Coral reefs are primarily composed of calcium carbonate (CaCO₃), which is produced by corals and other marine organisms through a process called calcification. As ocean acidity increases, the concentration of free carbonate ions (CO₃²⁻) decreases, making it more difficult for corals to extract the necessary materials to build their skeletons. This results in weaker coral structures and reduced growth rates .
3. Vulnerability to Stressors:
   • Weaker skeletons not only hinder growth but also increase corals’ vulnerability to physical damage from storms and predation by marine organisms. Research indicates that under high CO₂ conditions, corals may stop being productive and their risk of bleaching can increase by up to 50%.

Coral Bleaching

1. Symbiotic Relationships:
   • Corals rely on symbiotic algae known as zooxanthellae, which live within their tissues and provide essential nutrients through photosynthesis. Increased CO₂ levels can lead to higher sea temperatures, causing stress that results in coral bleaching—where corals expel these algae, leading to a loss of color and vital energy sources.
2. Long-Term Effects:
   • While corals can survive short-term bleaching events, prolonged stress can lead to increased mortality rates. The loss of zooxanthellae diminishes the coral’s ability to recover and thrive, ultimately threatening the entire reef ecosystem .

Broader Ecological Impacts

1. Loss of Biodiversity:
   • Coral reefs are biodiversity hotspots that support countless marine species. The degradation of coral reefs due to acidification and bleaching can lead to significant losses in biodiversity, impacting fish populations and other marine organisms that depend on healthy reef ecosystems for habitat and food.
2. Economic Consequences:
   • Coral reefs provide essential services, including coastal protection and tourism revenue. The decline of these ecosystems could cost economies billions in lost revenue from fishing and tourism industries .
3. Invasive Species:
   • Increased CO₂ levels can also favor the growth of invasive algal species that outcompete corals for space and resources, further destabilizing reef ecosystems