ACIDIFICAÇÃO DOS OCEANOS | Prof. Paulo Jubilut

How Do Oysters and Shellfish Build Their Shells?

The Role of the Mantle

• Oysters and shellfish are invertebrate mollusks that construct their shells using a tissue called the mantle.

• The mantle secretes proteins and calcium carbonate, which crystallize upon contact with water to form rigid structures known as shells.

Ocean Acidification: A Growing Concern

• Ocean acidification is a significant environmental issue linked to global warming, primarily caused by greenhouse gas emissions, especially carbon dioxide (CO2).

• CO2 emissions from fossil fuel combustion and deforestation have been increasing annually, leading to severe consequences for most living organisms on Earth.

Historical CO2 Levels

• A graph shows atmospheric CO2 levels over 400,000 years; it remained below 300 parts per million until around 1950 when it surged past 400 parts per million.

• This increase in atmospheric CO2 is directly responsible for ocean acidification.

Mechanism of Ocean Acidification

• Approximately 25% of atmospheric CO2 is absorbed by oceans, rivers, and lakes.

• When CO2 dissolves in water, it forms carbonic acid, which is unstable and dissociates into bicarbonate and hydrogen ions.

• An increase in hydrogen ions lowers the pH of ocean water, making it more acidic.

Impact on Marine Life

• Carbonate ions react with calcium in seawater to form calcium carbonate essential for coral skeleton formation and shell construction in mollusks.

• Increased acidity leads to less available carbonate for these reactions; thus marine animals struggle to build their shells or skeletons effectively.

Consequences of Reduced Calcium Carbonate

Effects on Calcifying Species

• A decrease in available calcium carbonate negatively impacts calcifying species like corals, mollusks (e.g., oysters), and crustaceans (e.g., crabs).

Structural Weaknesses

• Even with limited calcium carbonate availability, some animals can still produce weakened shells that are full of holes due to increased acidity dissolving their structures.

Broader Implications for Marine Ecosystems

Effects Beyond Calcifiers

• Fish also suffer from increased ocean acidity; it raises blood plasma acidity leading to a condition known as acidosis.

Plankton Disruption

• Acidification affects plankton organisms like foraminifera and coccolithophores crucial for marine food chains.

Historical Context & Future Solutions

Past Extinctions Linked to Acidification

• Evidence suggests that historical mass extinctions were caused by ocean acidification related to volcanic activity.

Mitigation Strategies

• To preserve marine species from extinction due to acidification effects, reducing atmospheric CO2 emissions through decreased fossil fuel use and deforestation is essential.

Understanding Exam Questions Related to Ocean Acidification

Common Misconceptions

• Clarifications about misconceptions regarding coral bleaching being linked solely to temperature increases rather than acidity changes.

Exam Preparation Tips:

• Understand how excess CO2 affects coral metabolism positively through enhanced photosynthesis rates among associated algae.