What Animals Are Affected by Ocean Acidification?

Ocean acidification, driven by the absorption of excess atmospheric carbon dioxide (CO2) into the ocean, disproportionately affects marine life that relies on calcium carbonate to build and maintain their shells and skeletons, as well as disrupting crucial physiological processes in a wide range of species. This pervasive threat impacts creatures from microscopic plankton to apex predators, potentially destabilizing entire marine ecosystems.

The Unfolding Crisis: A Chemical Imbalance

The ocean acts as a crucial carbon sink, absorbing approximately 30% of the CO2 released into the atmosphere by human activities. While this absorption helps mitigate climate change, it comes at a significant cost. When CO2 dissolves in seawater, it reacts with water molecules (H2O) to form carbonic acid (H2CO3). This acid then dissociates, releasing hydrogen ions (H+) and lowering the ocean’s pH. This process, known as ocean acidification, reduces the availability of carbonate ions (CO32-), a key building block for many marine organisms.

The scale of the problem is alarming. Since the pre-industrial era, the ocean’s pH has already decreased by about 0.1 pH units, representing a roughly 30% increase in acidity. While this may seem like a small change, the pH scale is logarithmic, meaning even minor shifts have significant impacts. Further acidification is inevitable as atmospheric CO2 concentrations continue to rise, threatening the long-term health and stability of marine ecosystems worldwide.

Shell Builders in the Crosshairs: Vulnerable Species

The most immediate and visible impacts of ocean acidification are seen in calcifying organisms, those that build their shells and skeletons from calcium carbonate. These organisms face a double whammy: reduced carbonate ion availability makes it more difficult to build and maintain their structures, and increased acidity can actively dissolve existing shells and skeletons. Some of the most vulnerable groups include:

• Shellfish: Oysters, clams, mussels, and scallops are all economically and ecologically important shellfish that are severely affected by ocean acidification. Their larval stages are particularly vulnerable, with reduced growth rates, abnormal shell formation, and increased mortality rates observed in acidified waters. This can lead to recruitment failures and population declines.

• Corals: Coral reefs, biodiversity hotspots that support a quarter of all marine life, are under severe threat. Ocean acidification reduces the ability of corals to build and maintain their calcium carbonate skeletons, making them more susceptible to bleaching, disease, and erosion. The loss of coral reefs has cascading effects on the entire ecosystem.

• Pteropods: These tiny, free-swimming marine snails are a crucial food source for many larger animals, including salmon, seabirds, and whales. Their delicate shells are highly vulnerable to dissolution in acidified waters, potentially disrupting entire food webs.

• Foraminifera and Coccolithophores: These microscopic plankton form the base of many marine food webs. Coccolithophores, with their intricate calcium carbonate plates, are particularly sensitive to acidification. Changes in their abundance and composition can have far-reaching consequences for ocean productivity and carbon cycling.

Beyond Shells: Physiological Impacts on Marine Life

The effects of ocean acidification extend beyond shell formation, impacting a wide range of physiological processes in various marine species. Even animals that don’t build calcium carbonate structures can be negatively affected.

• Fish: Studies have shown that ocean acidification can affect fish behavior, including their ability to detect predators and find suitable habitats. It can also impact their growth rates, reproductive success, and oxygen uptake.

• Cephalopods: While some cephalopods, like squid, have shown resilience to ocean acidification in some studies, others, like cuttlefish, exhibit impaired growth and development in acidified conditions.

• Echinoderms: Sea urchins and starfish are also vulnerable to ocean acidification, with studies showing negative impacts on their larval development, growth, and immune function.

Cascading Effects: Disrupting Marine Ecosystems

The impacts of ocean acidification are not isolated to individual species. They can ripple through entire marine ecosystems, altering food web dynamics, species distributions, and ecosystem functions. The loss of key species, like corals or pteropods, can have cascading effects on the entire community, leading to dramatic shifts in ecosystem structure and function.

Frequently Asked Questions (FAQs)

1. What is the difference between ocean acidification and climate change?

While both are driven by increased atmospheric CO2, they are distinct processes. Climate change refers to the broader changes in Earth’s climate, including rising temperatures, altered precipitation patterns, and sea-level rise. Ocean acidification specifically refers to the decrease in the pH of the ocean caused by the absorption of CO2. While related, they have different impacts on marine ecosystems.

2. How does ocean acidification affect the food chain?

Ocean acidification primarily affects the base of the food chain, impacting plankton and calcifying organisms. Reductions in their abundance or changes in their species composition can have cascading effects on higher trophic levels, disrupting the entire food web.

3. Can anything be done to reverse ocean acidification?

The most effective way to reverse ocean acidification is to reduce atmospheric CO2 emissions. This requires a global effort to transition to renewable energy sources, improve energy efficiency, and reduce deforestation. While geoengineering solutions have been proposed, they are often controversial and have potentially unknown consequences.

4. Are all marine organisms equally affected by ocean acidification?

No, different species have different sensitivities to ocean acidification. Calcifying organisms are generally more vulnerable, but even non-calcifying organisms can be affected through various physiological mechanisms.

5. How is ocean acidification being monitored?

Scientists use a variety of methods to monitor ocean acidification, including measuring pH, dissolved CO2, and alkalinity at various locations and depths in the ocean. They also conduct laboratory experiments to assess the impacts of acidification on different marine species.

6. What is the role of ocean currents in distributing ocean acidification?

Ocean currents play a significant role in distributing acidified water around the globe. Upwelling currents can bring deep, acidic waters to the surface, exposing shallow-water ecosystems to increased acidity.

7. How does ocean acidification interact with other stressors, such as pollution and warming waters?

Ocean acidification often interacts synergistically with other stressors, such as pollution, warming waters, and overfishing. This means that the combined effects of these stressors can be greater than the sum of their individual effects. For example, corals that are already stressed by warming waters are even more vulnerable to ocean acidification.

8. Is ocean acidification happening everywhere in the ocean?

While ocean acidification is a global phenomenon, the rate and extent of acidification vary geographically. Certain regions, such as the Arctic and Antarctic, are particularly vulnerable due to the cold temperatures and lower pH of the water. Coastal areas are also susceptible due to pollution and nutrient runoff.

9. What are the economic consequences of ocean acidification?

Ocean acidification has significant economic consequences, particularly for fisheries, aquaculture, and tourism. Declines in fish stocks and shellfish populations can impact food security and livelihoods. The loss of coral reefs can damage tourism industries and increase coastal erosion.

10. Can marine organisms adapt to ocean acidification?

Some marine organisms may have the potential to adapt to ocean acidification over time, but the rate of adaptation may not be fast enough to keep pace with the rapid rate of acidification. Furthermore, adaptation may come at a cost, such as reduced growth rates or reproductive success.

11. What is the impact of ocean acidification on deep-sea ecosystems?

Deep-sea ecosystems are also vulnerable to ocean acidification. Cold temperatures and high pressures in the deep sea can exacerbate the effects of acidification on calcifying organisms. Deep-sea corals and other vulnerable species are at risk.

12. What can individuals do to help address ocean acidification?

Individuals can help address ocean acidification by reducing their carbon footprint. This includes driving less, using public transportation, conserving energy, eating locally sourced food, and supporting policies that promote renewable energy and reduce greenhouse gas emissions. Educating others about the issue is also crucial.