Ocean acidification

A recent study published in Global Change Biology reveals that ocean acidification crossed a critical “planetary boundary” five years ago, by 2020. This alarming finding indicates that the world’s oceans are nearing or have already entered a “danger zone” for acidity, primarily due to the absorption of excess atmospheric carbon dioxide.

Key Findings:

• Planetary Boundary Breached: Scientists determined that this boundary is crossed when calcium carbonate levels (essential for marine shell development) fall below 20% of pre-industrial levels. The new report places this figure at approximately 17%, confirming the breach.
• Cause of Acidification: Since the Industrial Revolution, the burning of fossil fuels and land-use changes have increased atmospheric CO2. Oceans absorb about 30% of this CO2. When absorbed by seawater, CO2 triggers chemical reactions that increase hydrogen ion concentration, making the water more acidic and reducing the availability of carbonate ions.
• Impact on Marine Life:
  • Calcifying Organisms: Decreased carbonate ions make it difficult for organisms like oysters, clams, sea urchins, and corals to build and maintain their shells and skeletons.
  • Habitat Loss:
    • Tropical and subtropical reefs have lost over 40% of their habitats.
    • Sea butterflies (crucial to polar marine food webs) have lost over 60% of their habitats.
    • Coastal shellfish species have lost 13% of their functional habitats.
  • Behavioral Changes: Even non-calcifying organisms are affected; some fish exhibit decreased ability to detect predators in more acidic waters.
• Food Web Implications: The risks posed to these organisms threaten the stability of entire marine food webs.