16.2 Ocean acidification and its impacts on calcifying organisms
3 min read•july 22, 2024
Ocean acidification, caused by rising atmospheric CO2, is making our seas more acidic. This process threatens marine life, especially organisms that build shells or skeletons from calcium carbonate. The effects ripple through ecosystems, impacting biodiversity and food webs.
The consequences of ocean acidification extend beyond ecology. It poses risks to fisheries, coastal tourism, and infrastructure. Understanding these impacts is crucial for developing strategies to protect our oceans and the communities that depend on them.
Ocean Acidification and Its Effects
Ocean acidification and atmospheric CO2
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- Ocean acidification is the ongoing decrease in the pH levels of the Earth's oceans primarily caused by the absorption of carbon dioxide (CO2) from the atmosphere
- Atmospheric CO2 levels have been increasing due to human activities such as burning of fossil fuels (coal, oil, natural gas), deforestation, and cement production
- When atmospheric CO2 dissolves in seawater, it forms carbonic acid (H2CO3) which dissociates into hydrogen ions (H+) and bicarbonate ions (HCO3-)
- Increased H+ concentration lowers the pH of the seawater, making it more acidic (lemon juice, vinegar)
- Since the industrial revolution, the average pH of the ocean surface has decreased by approximately 0.1 units corresponding to a 30% increase in acidity
Calcification in marine organisms
- is the process by which marine organisms build calcium carbonate (CaCO3) structures such as shells (oysters, mussels), exoskeletons (crabs, lobsters), and
- Calcifying organisms use dissolved carbonate ions (CO32-) and calcium ions (Ca2+) from seawater to form CaCO3 through the reaction:
- Ocean acidification reduces the availability of carbonate ions in seawater as increased H+ concentration favors the (HCO3-) over carbonate ions (CO32-)
- Lower CO32- concentration makes it more difficult for calcifying organisms to build and maintain their CaCO3 structures leading to thinner, weaker, or deformed shells and skeletons
- Reduced calcification rates increase vulnerability to predation (crabs, fish), physical damage (waves, storms), and other stressors (temperature, pollution)
Vulnerable species to acidification
- Corals secrete CaCO3 exoskeletons to form the foundation of coral reefs and reduced calcification rates can slow coral growth and weaken reef structures (Great Barrier Reef, Caribbean reefs)
- Mollusks such as oysters, mussels, and pteropods (sea butterflies) rely on CaCO3 shells for protection and support with thinning or deformed shells increasing vulnerability
- Calcifying plankton including coccolithophores and foraminifera form CaCO3 plates or tests that contribute to marine sediments and carbon cycling with decreased calcification affecting their survival and role in marine food webs (base of the food chain)
Consequences of ocean acidification
- Ecological consequences include:
- Reduced biodiversity in marine ecosystems from loss of sensitive calcifying species and alteration of community structure and food web dynamics
- Degradation of coral reefs leading to loss of habitat for numerous marine species (fish, invertebrates) and decreased coastal protection from storms and erosion
- Changes in biogeochemical cycles with altered carbon and nutrient cycling due to shifts in plankton communities
- Economic consequences encompass:
- Impacts on fisheries and aquaculture from declines in commercially valuable populations (oysters, mussels, clams) and reduced yields and increased production costs
- Tourism and recreation losses due to degradation of coral reefs and other marine attractions resulting in decreased revenue for coastal communities and businesses
- Coastal infrastructure damage with increased vulnerability to storms and sea-level rise due to weakened coral reefs and higher costs for coastal protection and restoration projects
Key Terms to Review (18)
Acid-base regulation: Acid-base regulation refers to the mechanisms organisms use to maintain the pH balance of their internal environment, ensuring that bodily functions operate optimally. This regulation is crucial for marine organisms, especially calcifying species, as changes in pH can affect their ability to build and maintain calcium carbonate structures. In the context of ocean acidification, understanding these regulatory mechanisms becomes essential as elevated CO2 levels lead to lower ocean pH, impacting marine life and ecosystems.
Behavioral plasticity: Behavioral plasticity refers to the ability of an organism to change its behavior in response to environmental changes or challenges. This adaptability is crucial for survival, particularly for species affected by rapid alterations in their habitats, such as those caused by changing ocean conditions. Organisms displaying behavioral plasticity can adjust their behaviors in ways that help them cope with stressors like ocean acidification, impacting their feeding, reproduction, and interaction with their environment.
Biomineralization: Biomineralization is the process by which living organisms produce minerals to harden or stiffen existing tissues. This natural phenomenon plays a critical role in the formation of structures such as shells, bones, and coral, enabling organisms to survive in various environments. It involves biochemical processes where organic compounds interact with inorganic materials, leading to the creation of composite materials that serve specific functions within an organism's life cycle.
Bleaching Events: Bleaching events refer to the process in which coral reefs lose their vibrant colors and become pale or white due to stress factors, primarily from increased water temperatures and other environmental changes. These stressors lead to the expulsion of symbiotic algae called zooxanthellae, which provide corals with essential nutrients and color. Without these algae, corals not only lose their color but also their main source of energy, making them more susceptible to disease and mortality.
Calcification: Calcification is the process by which organisms, particularly marine organisms like corals, mollusks, and some plankton, produce calcium carbonate (CaCO₃) to form their skeletal structures or shells. This process is essential for the growth and stability of coral reefs and plays a significant role in marine ecosystems, influencing biodiversity and the overall health of ocean environments.
Carbon dioxide absorption: Carbon dioxide absorption refers to the process by which carbon dioxide (CO2) is taken up from the atmosphere into the ocean. This process plays a crucial role in regulating global climate and ocean chemistry, as it affects the pH levels of seawater, leading to ocean acidification. As CO2 dissolves in seawater, it reacts with water to form carbonic acid, which subsequently lowers the pH and has significant impacts on marine ecosystems, particularly for organisms that rely on calcium carbonate for their skeletal structures.
Coral reefs: Coral reefs are diverse underwater ecosystems made up of colonies of coral polyps that build calcium carbonate structures, providing habitat and shelter for a wide variety of marine life. They play a crucial role in marine biodiversity and serve as essential components of coastal protection, nutrient cycling, and fishery support.
Disruption of food webs: Disruption of food webs refers to the alteration or destabilization of the complex interdependent relationships between organisms in an ecosystem, particularly through changes in population dynamics or environmental conditions. Such disruptions can lead to cascading effects, impacting not only individual species but also the entire ecosystem's structure and function. One significant factor contributing to these disruptions is ocean acidification, which negatively affects calcifying organisms that play crucial roles in marine food webs.
Dissolution of calcium carbonate: The dissolution of calcium carbonate refers to the process by which calcium carbonate (CaCO₃) dissolves in water, particularly in the presence of carbonic acid formed when CO₂ is dissolved in water. This process is crucial in understanding how ocean acidification affects marine ecosystems, especially those involving organisms that rely on calcium carbonate for their shells and skeletons, such as corals and mollusks.
Fishery impacts: Fishery impacts refer to the various effects that fishing activities have on marine ecosystems, particularly concerning the populations of fish and other organisms. These impacts can lead to changes in species composition, declines in fish stocks, and alterations in the structure of marine habitats. Understanding these consequences is essential for managing fisheries sustainably and mitigating negative effects on marine biodiversity.
Formation of bicarbonate ions: The formation of bicarbonate ions (HCO₃⁻) occurs when carbon dioxide (CO₂) dissolves in seawater and reacts with water, leading to the creation of carbonic acid (H₂CO₃), which then dissociates into bicarbonate and hydrogen ions. This process is vital for buffering ocean pH and plays a critical role in the carbon cycle, especially in the context of ocean acidification and its effects on marine life, particularly organisms that rely on calcium carbonate for their shells and skeletons.
In situ experiments: In situ experiments refer to scientific investigations conducted in the natural environment of the organisms being studied, rather than in controlled laboratory settings. These experiments allow researchers to observe and measure the effects of environmental factors, such as changes in ocean chemistry, directly on organisms like corals and shellfish. By maintaining the ecological context, in situ experiments provide insights into real-world interactions and responses, especially relevant in understanding the impacts of ocean acidification on calcifying organisms.
Katherine Y. Allen: Katherine Y. Allen is a prominent marine biologist known for her research on ocean acidification and its effects on marine ecosystems, particularly on calcifying organisms like corals and shellfish. Her work has highlighted the urgent need to understand how rising CO2 levels impact these species, which are essential for biodiversity and marine food webs.
Laboratory simulations: Laboratory simulations are controlled experiments that mimic real-world processes, allowing researchers to study complex systems in a safe and manageable environment. These simulations provide insights into how organisms respond to varying conditions, such as changes in pH or temperature, which is crucial for understanding phenomena like ocean acidification and its impacts on calcifying organisms. By replicating specific environmental conditions, these simulations help to predict potential outcomes and inform conservation strategies.
NOAA: NOAA, or the National Oceanic and Atmospheric Administration, is a scientific agency within the United States Department of Commerce focused on understanding and predicting changes in climate, weather, oceans, and coasts. NOAA plays a crucial role in monitoring ocean acidification, a significant environmental issue that impacts marine ecosystems, particularly calcifying organisms like corals and shellfish, by providing essential data and research that help inform policies and conservation efforts.
PH reduction: pH reduction refers to the decrease in pH levels, indicating an increase in acidity in a solution. This phenomenon is significant in marine environments, especially due to the absorption of atmospheric carbon dioxide by oceans, leading to ocean acidification. As pH levels drop, it can adversely affect various marine organisms, particularly those that rely on calcium carbonate for their shells and skeletons, such as corals and mollusks.
Shellfish: Shellfish are aquatic animals that have a shell, including both crustaceans like shrimp and crabs, and mollusks such as clams and oysters. These creatures play a crucial role in marine ecosystems and are significant for their economic value, particularly in aquaculture and fisheries. Shellfish are also affected by environmental changes, such as ocean acidification, which can impact their growth and survival due to their reliance on calcium carbonate for their shells.
Tourism decline: Tourism decline refers to a significant decrease in the number of visitors to a destination, often leading to negative impacts on local economies, ecosystems, and cultural sites. This phenomenon can be driven by various factors, including environmental issues, economic downturns, or global events that deter travel. When tourism declines, communities that depend on it for income and employment may struggle to adapt, which can further exacerbate existing environmental challenges.