Ocean Acidification and Its Threat to Marine Life

Ocean Acidification: An Overview

• The world produces approximately 35 billion tons of CO_2 annually, and this amount is not decreasing.
• A significant portion of these emissions enters the atmosphere, contributing to the greenhouse effect.
• About 25% of human-caused CO_2 emissions are absorbed by the oceans.
• Increased CO_2 emissions lead to greater absorption by the ocean, resulting in acidification.

The Chemistry of Ocean Acidification

• The ocean's natural pH is around 8.1, which is slightly alkaline.

• pH measures acidity, specifically the concentration of hydrogen ions (H^+).

• Higher concentration of hydrogen ions (H^+) indicates lower pH and higher acidity.

• When CO2 is absorbed by the ocean, it dissolves in water (H2O) to form carbonic acid (H2CO3).

• Carbonic acid dissociates into bicarbonates (HCO_3^-) by releasing hydrogen ions (H^+).

  CO2 + H2O \rightleftharpoons H2CO3 \rightleftharpoons HCO_3^- + H^+

• The increase in hydrogen ions (H^+) raises the ocean's acidity.

• Since pre-industrial times, the ocean's pH has decreased by approximately 0.1 pH units.

• Due to the logarithmic nature of the pH scale, a decrease of 0.1 pH units represents about a 30% increase in acidity.

Impacts on Marine Ecosystems

• Increased acidity can devastate marine ecosystems, especially calcifiers.
• Calcifiers include:
  • Corals
  • Sea urchins
  • Mollusks (e.g., oysters)
• Acidification reduces the availability of calcium carbonate (CaCO_3), which is essential for calcifiers to build skeletons and shells.
• Calcium (Ca^{2+}) competes with hydrogen ions (H^+) to associate with carbonate (CO_3^{2-}).
• Higher H^+ concentration means less CaCO_3 is formed.
• Some species might adapt to acidification by allocating energy to adaptation mechanisms, making them weaker and less resilient to other threats like pollution.
• Coral reefs are crucial habitats and feeding grounds for many fish and invertebrates, supporting high biodiversity.
• Reef destruction due to acidification can negatively impact non-calcifiers (e.g., fish) through indirect effects on food chains.
• Phytoplankton, like pteropods, are also affected by acidification, which can further disrupt marine food webs.

Socioeconomic Impacts

• Approximately one in seven people worldwide rely on aquaculture and fisheries for food.
• Decreasing yields from mollusks and fish can have considerable socioeconomic consequences, especially in highly dependent regions.
• Studies suggest that the quality of yields is also decreasing, with reductions in proteins and lipids, potentially exacerbating malnutrition in coastal communities.
• Ocean acidification can harm tourism, such as in Australia, where 2 million tourists visit annually specifically for the reefs.
• Reefs offer flood protection and prevent coastal erosion.

Potential Solutions

• Mitigating CO_2 emissions is the most effective long-term solution.
• Adaptation and protection measures are also needed due to the existing impacts of acidification.
• Conventional methods:
  • Establishing protection areas.
  • Reducing other stress factors, such as water pollution.
• Less conventional methods:
  • Cultivating seaweed farms near vulnerable areas to act as local CO_2 sinks, reducing acidity in surrounding waters.

Additional Considerations

• Ocean warming and decreasing oxygen levels can synergize with acidification, exacerbating the negative effects on marine ecosystems.
• Ocean acidification poses a significant threat to marine ecosystems and the ecosystem services they provide.
• Formation of shells in animals
• Shells of animals formed primarily of calcium carbonate
• Calcium carbonate is formed when calcium ions bind with carbonate molecules
• Ocean acidification begins with c o two emissions
• C o two produced when fossil fuels burned
• Once in air, c o two is absorbed into ocean through wave action
• C o two combines with water to form carbonic acid
• Carbonic acid breaks down into bicarbonate molecules
• Carbonate usually forms shells binds easily with hydrogen ions
• In acidic ocean, abundant hydrogen ions bind to carbonate an prevent shell formation.