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 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.

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.

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.

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.

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.