Ocean Acidification and Coral Reefs

The Potential Consequences of Coral Bleaching Caused by Ocean Acidification

Coral bleaching is a phenomenon that occurs when corals expel their symbiotic algae due to changes in environmental conditions such as increased water temperature or ocean acidification. The potential consequences of coral bleaching caused by ocean acidification are significant and have already led to the decline of coral reefs worldwide.ref.8.6 ref.14.18 ref.23.7 Mass coral bleaching events have become more frequent and severe, and model predictions suggest that this trend will continue to accelerate over the course of this century.ref.23.125 ref.23.7 ref.99.25

Ocean acidification, which is the decrease in seawater pH due to the absorption of excessive carbon dioxide (CO2) emissions, plays a crucial role in coral bleaching. It decreases the concentration of carbonate ions, which are essential for reef calcifiers to construct their calcium carbonate skeletons.ref.23.125 ref.23.8 ref.15.5 This lowers the saturation state of calcium carbonate and increases rates of carbonate erosion on coral reefs. The projected levels of acidification for tropical oceans over the next few decades are expected to shift the balance between calcification and dissolution on coral reefs, significantly impacting their health and dynamics.ref.23.125 ref.23.8 ref.23.125

Furthermore, the combined effects of ocean warming and acidification are predicted to amplify under higher CO2 emission scenarios. Coral reefs are at risk of rapid and terminal decline at atmospheric CO2 concentrations of 450 parts per million (ppm), resulting in mass bleaching, ocean acidification, and local environmental impacts.ref.99.25 ref.23.125 ref.99.25 The degradation of coral reefs leads to declines in biodiversity, reduced protection of coasts from storm surges, and the loss of tourism revenues. The impacts of coral reef degradation on ecosystem services and people's livelihoods are observed primarily in severely degraded reefs and often after substantial lag times.ref.15.5 ref.23.6 ref.23.125

The consequences of ocean acidification on coral reefs are complex and depend on various factors, including species-specific responses, adaptation mechanisms, and interactions among global change drivers. The effects of ocean acidification on coral reefs are not limited to coral growth but also extend to reproduction and survivorship.ref.15.5 ref.65.39 ref.15.5 Therefore, it is crucial to understand the long-term implications of ocean acidification on the resilience and recovery of coral reefs.ref.65.39 ref.23.8 ref.23.125

The Long-Term Implications of Ocean Acidification on Coral Reef Resilience and Recovery

Ocean acidification, caused by the absorption of excessive CO2 emissions, leads to a decrease in seawater pH and a reduction in carbonate ions, which are essential for the construction of coral skeletons and reefs. This results in decreased calcification rates of corals and coralline algae, as well as increased rates of bioerosion and dissolution of carbonate sediments.ref.23.125 ref.23.8 ref.15.5 The combined impacts of ocean warming and acidification are predicted to amplify under higher CO2 emission scenarios.ref.23.125 ref.23.125 ref.15.5

The reduction in calcification rates and increased rates of bioerosion and dissolution have profound implications for the health and viability of coral reef ecosystems. Global estimates suggest that under business-as-usual scenarios, most reefs will likely suffer net erosion by 2100.ref.1.16 ref.21.3 ref.23.125 The capacity for reef-building taxa to tolerate marine heatwaves, ongoing ocean warming, and acidification is largely unknown, and the ability of corals to adapt to these changes is uncertain.ref.1.16 ref.23.125 ref.1.16

Coral reefs are already being harmed by a combination of warming and acidification, leading to increased coral bleaching and death. The frequency and severity of bleaching events are projected to accelerate over this century, further impacting the global health of coral reef ecosystems.ref.23.7 ref.23.125 ref.23.125 The acidification of seawater reduces the ability of corals to recover and decreases their net growth rate.ref.23.125 ref.23.125 ref.15.5

Moreover, the impacts of ocean acidification on coral reefs interact with other environmental stressors, such as nutrient pollution and human disturbance, in additive and synergistic ways. These stressors compound the challenges faced by coral reefs and further hinder their resilience and recovery.ref.15.16 ref.15.5 ref.70.6

The Sensitivity of Future Coral Reef Growth to Ocean Warming and Acidification

The future growth of coral reefs is highly sensitive to ocean warming and acidification. Under business-as-usual scenarios, most reefs are projected to suffer net erosion by 2100.ref.23.125 ref.23.126 ref.1.8 The capacity of reef-building taxa to tolerate marine heatwaves, ongoing ocean warming, and acidification is largely unknown, and the ability of corals to adapt to these changes is uncertain.ref.1.16 ref.23.125 ref.1.16

It is crucial to understand the complex and species-specific responses of calcifying species to variations in seawater chemistry. Calcifying reef-builders, such as corals and calcifying algae, are photoautotrophs with algal symbionts, which complicates their physiological response to changes in seawater chemistry.ref.28.10 ref.22.0 ref.16.33 The response of calcifying species to variation in seawater chemistry is complex and not uniform across all species.ref.3.46 ref.16.33 ref.3.46

The uncertainties surrounding the future growth of coral reefs highlight the need for further research to better understand the physiological responses and adaptive mechanisms of corals and other reef-building organisms. These studies will contribute to a more comprehensive understanding of the potential impacts of ocean warming and acidification on coral reef ecosystems.ref.23.126 ref.1.8 ref.14.3

Adaptive Mechanisms and Strategies of Coral Reefs in Coping with Ocean Acidification

There is evidence to suggest that coral reefs employ adaptive mechanisms and strategies to cope with ocean acidification. Exposure to variability in CO2 chemistry, specifically low pH events, can enhance the adaptive capacity of non-photosynthesizing calcifiers, potentially reducing their vulnerability to ocean acidification.ref.23.10 ref.23.177 ref.23.8 This indicates that some organisms may possess the ability to adapt to changes in seawater chemistry.ref.23.55 ref.65.40 ref.23.10

Additionally, coral reef communities that are naturally more resistant or resilient to climate change, known as climate change refugia, may be less sensitive to shifts in ocean temperature and chemistry, including ocean acidification. These climate change refugia could potentially serve as sources of coral larvae and contribute to the recovery of damaged coral reefs.ref.23.10 ref.23.124 ref.23.177

Furthermore, reducing other stressors on coral reefs, such as overfishing and pollution, through targeted local management actions can help mitigate the impacts of ocean acidification. By reducing these stressors, the overall resilience and adaptive capacity of coral reefs can be enhanced.ref.15.16 ref.23.154 ref.15.16

While these findings indicate that coral reefs have the potential to adapt and mitigate the effects of ocean acidification, further research is needed to fully understand the extent of their adaptive capabilities. Continued research and monitoring efforts are crucial to inform effective management and conservation strategies for coral reefs in the face of ongoing ocean acidification.ref.65.39 ref.23.177 ref.23.126

In conclusion, ocean acidification has significant long-term implications for the resilience and recovery of coral reefs. It reduces calcification rates, increases bioerosion and dissolution, and decreases the ability of corals to recover and grow.ref.23.125 ref.23.8 ref.15.5 These impacts interact with other stressors and pose a major challenge to the survival of coral reef ecosystems. However, there is evidence to suggest that coral reefs possess adaptive mechanisms and strategies that may help them cope with ocean acidification.ref.15.16 ref.23.8 ref.15.16 Further research is needed to better understand these mechanisms and develop effective management strategies to protect and conserve coral reefs in the face of ongoing ocean acidification.ref.23.125 ref.65.39 ref.15.16

Ocean Acidification and Marine Life

Species-Specific Vulnerabilities and Sensitivities to Ocean Acidification

The physiological and behavioral responses of different marine organisms to ocean acidification vary depending on the species. Calcifying organisms, such as mollusks, crustaceans, corals, and some types of algae, are particularly vulnerable to ocean acidification.ref.35.36 ref.26.31 ref.27.31 The decrease in carbonate ion concentrations in acidified seawater can reduce the ability of these organisms to form shells and skeletons, leading to reduced calcification rates and shell mineralization. This vulnerability is due to the fact that these organisms rely on carbonate ions to build and maintain their hard structures.ref.26.32 ref.27.32 ref.35.36

In addition to reduced calcification, ocean acidification can have diverse effects on whole organism function. For example, it can impair immunological function, disrupt acid-base balance, and impact growth, reproduction, and ecosystem effects.ref.75.8 ref.69.3 ref.69.3 These effects can vary depending on the specific species and their physiological and ecological characteristics. For instance, some finfish species have shown behavioral changes related to ocean acidification, such as increased boldness or anxiety.ref.69.3 ref.70.6 ref.69.3 However, it is not yet known if these behavioral changes will be observed across many other finfish species.ref.69.3 ref.51.34 ref.70.6

It is also important to note that the impact of ocean acidification on marine species is highly species-specific. Different marine organisms may demonstrate differing levels of vulnerability to the change in oceanic chemistry.ref.69.3 ref.69.3 ref.35.36 While calcifying organisms tend to demonstrate reduced calcification and survival in an acidifying ocean, it is not yet well understood to what degree organisms can adapt to quasi-permanent changes in ocean pH due to rapid anthropogenic carbon input. Furthermore, the effects of ocean acidification on individual organisms' responses and how they scale up to cause population-scale responses are largely unknown.ref.25.3 ref.32.0 ref.35.41 Therefore, more research is needed to fully understand the species-specific vulnerabilities and sensitivities to the effects of ocean acidification.ref.35.41 ref.35.41 ref.2.31

Influence on the Distribution and Abundance of Marine Species

Ocean acidification can influence the distribution and abundance of marine species in several ways. Firstly, it can directly affect organism physiology, particularly in calcifying organisms such as mollusks, crustaceans, corals, and some types of algae, leading to reduced calcification and survival.ref.69.3 ref.75.8 ref.69.3 This is due to the decrease in carbonate saturation in the water, which makes it more difficult for these organisms to form their shells or skeletons. The reduction in calcification and survival can have significant impacts on the distribution and abundance of these species, as they may struggle to maintain their populations in an acidifying ocean.ref.75.8 ref.69.3 ref.35.36

Additionally, ocean acidification can indirectly impact marine species by disrupting food webs or altering physical habitats. Changes in pH can affect the availability and quality of food sources for different species, which can have cascading effects on the abundance and distribution of organisms throughout the food chain.ref.69.3 ref.69.3 ref.75.8 For example, if the primary producers, such as phytoplankton, are negatively affected by ocean acidification, it can reduce the availability of food for herbivores and subsequently impact the abundance of higher trophic levels. Similarly, if calcifying organisms, which are an important food source for many species, decline in abundance, it can have cascading effects on the entire food web.ref.69.3 ref.75.8 ref.52.32

Furthermore, ocean acidification can also lead to changes in behavior in some species, such as increased boldness or anxiety. These behavioral changes can affect the distribution and abundance of species by altering their foraging patterns, predator-prey interactions, and habitat utilization.ref.69.3 ref.69.3 ref.70.6 However, the extent of these behavioral changes and their effects on other finfish species are not yet fully understood.ref.69.3 ref.70.6 ref.36.35

It is important to note that the impacts of ocean acidification on marine species can be highly species-specific. The responses observed in laboratory studies may not always translate to population-scale responses in the natural environment.ref.69.3 ref.69.3 ref.51.34 Therefore, it is crucial to conduct further research to fully understand the specific mechanisms through which ocean acidification influences the distribution and abundance of marine species.ref.35.41 ref.35.41 ref.36.35

Cascading Effects on Food Webs and Trophic Interactions

The cascading effects of ocean acidification on food webs and trophic interactions in marine ecosystems are significant. Ocean acidification can negatively impact calcifying organisms such as mollusks, crustaceans, corals, and some types of algae.ref.69.3 ref.75.8 ref.69.3 These organisms experience reduced calcification, growth, survival, development, and abundance across a wide range of taxa. The decrease in carbonate ion concentrations in acidified seawater makes it more difficult for these organisms to form their shells or skeletons, leading to a decline in their populations.ref.75.8 ref.35.36 ref.69.3

However, it is important to note that not all marine organisms respond negatively to ocean acidification. Some non-calcifying plants and microalgae may actually respond positively to acidification by increasing their photosynthetic and growth rates.ref.75.8 ref.75.8 ref.69.3 This response can have implications for the structure and dynamics of food webs, as the availability and abundance of primary producers can influence the entire trophic pyramid.ref.52.32 ref.35.39 ref.52.32

The effects of ocean acidification on marine viruses and their microbial hosts are still controversial, with different responses depending on the trophic state and successional stage of the plankton community. Some studies suggest that ocean acidification may enhance viral infection rates, while others propose that it may have minimal or even inhibitory effects.ref.44.38 ref.44.31 ref.44.72 Further research is needed to understand the complex interactions between viruses, microbial hosts, and ocean acidification.ref.44.72 ref.44.38 ref.44.31

Additionally, ocean acidification can disrupt food webs, alter physical habitats, and affect nutrient cycling. Changes in pH can impact the availability and quality of food sources for different species, which can have far-reaching consequences for biodiversity, ecosystem functioning, and the provision of ecosystem services.ref.59.3 ref.69.3 ref.52.32 For example, if the primary producers are negatively affected by ocean acidification, it can lead to reduced energy flow through the food web and a decline in the overall productivity of the ecosystem. Furthermore, changes in physical habitats, such as coral reefs, can have cascading effects on the organisms that rely on these habitats for food, shelter, and protection.ref.52.32 ref.69.3 ref.75.8

In conclusion, ocean acidification poses a significant threat to marine ecosystems and the services they provide. The physiological and behavioral responses of different marine organisms to ocean acidification vary depending on the species, with calcifying organisms being particularly vulnerable.ref.75.8 ref.69.3 ref.69.3 Ocean acidification can influence the distribution and abundance of marine species through direct physiological impacts, indirect effects on food webs, and alterations to physical habitats. Furthermore, the cascading effects of ocean acidification on food webs and trophic interactions can have far-reaching consequences for biodiversity and ecosystem functioning.ref.69.3 ref.69.3 ref.75.8 However, there is still much to be understood about the specific vulnerabilities and sensitivities of different species to ocean acidification, as well as the mechanisms through which these effects propagate through ecosystems. Therefore, further research is needed to fully understand and mitigate the effects of ocean acidification on marine ecosystems.ref.35.41 ref.69.3 ref.69.3

Overall Health of Oceans

The Interactions of Ocean Acidification with Other Stressors

Ocean acidification is not the only stressor that marine ecosystems face. It interacts with other stressors such as temperature, pollution, and nutrient pollution in additive and synergistic ways.ref.70.6 ref.52.45 ref.65.21 These interactions can have significant impacts on the overall health and functioning of oceans. Changes in sea surface temperatures, salinity, oxygen levels, and circulation patterns, which are tied to carbon emissions, also contribute to the overall health of oceans.ref.70.6 ref.52.41 ref.52.41

The combination of warming and acidification has already been observed to harm coral reef ecosystems. Coral reefs are highly susceptible to the impacts of ocean acidification, as the decrease in pH inhibits the ability of corals to build their calcium carbonate skeletons.ref.23.8 ref.15.5 ref.23.125 This leads to decreased calcification rates and weaker coral structures. Additionally, the increase in temperature associated with climate change further exacerbates the stress on coral reefs, leading to coral bleaching events and increased mortality.ref.23.7 ref.23.8 ref.23.7

Furthermore, other non-climate change-related stressors, including human use and disturbance of marine systems, can interact with ocean acidification to further impact the health of oceans. For example, nutrient pollution from agricultural runoff and wastewater discharge can lead to eutrophication, which promotes the growth of harmful algal blooms.ref.70.6 ref.70.7 ref.15.5 These algal blooms can deplete oxygen levels in the water, creating hypoxic or anoxic conditions that are detrimental to marine life. When combined with ocean acidification, these stressors can have compounding effects on marine ecosystems.ref.15.5 ref.75.8 ref.15.5

To better understand the effects of ocean acidification on marine ecosystems, it is important to conduct research that assesses the impacts of multiple stressors and considers the variability in environmental conditions. This will allow scientists to determine the specific mechanisms by which these stressors interact and affect marine organisms.ref.65.21 ref.35.41 ref.69.3 By studying these interactions, researchers can develop more accurate predictions and management strategies to mitigate the impacts of ocean acidification on marine ecosystems.ref.35.40 ref.65.21 ref.35.41

Potential Feedback Loops between Ocean Acidification and Environmental Changes

Ocean acidification can potentially lead to feedback loops with other environmental changes, further exacerbating the impacts on marine ecosystems. These feedback loops can occur through changes to sea surface temperatures, salinity, oxygen levels, and circulation patterns.ref.70.6 ref.69.3 ref.69.3

Changes in sea surface temperatures can influence the rate at which carbon dioxide is absorbed by the ocean. Warmer waters have a reduced capacity to absorb CO2, which can lead to an increase in atmospheric CO2 concentrations.ref.52.44 ref.62.3 ref.52.32 This, in turn, contributes to further ocean acidification. Additionally, changes in temperature can affect the metabolic rates and physiological processes of marine organisms, potentially altering their ability to adapt to changing ocean conditions.ref.62.3 ref.62.3 ref.52.32

Ocean acidification can also alter the development and behavior of many finfish species. The decrease in pH can affect the sensory systems of fish, impairing their ability to detect predators, find food, and navigate their surroundings.ref.70.5 ref.70.6 ref.69.3 This can have cascading effects on the food web, impacting the abundance and distribution of fish populations.ref.40.75 ref.70.5 ref.69.3

Furthermore, other non-climate change-related stressors such as nutrient pollution and human use and disturbance of marine systems can interact with ocean acidification in additive and synergistic ways. Nutrient pollution can increase the availability of nutrients in the water, leading to increased primary productivity.ref.70.6 ref.70.7 ref.59.3 This can result in the formation of algal blooms, which can further deplete oxygen levels and create hypoxic conditions. When combined with ocean acidification, these stressors can have compounding effects on marine organisms.ref.15.5 ref.59.3 ref.70.7

The interactive effects of ocean warming and CO2-driven acidification on larval development are largely unexplored. Larval stages of many marine organisms are particularly vulnerable to environmental changes, and any disruptions in their development can have long-lasting impacts on population dynamics and biodiversity.ref.53.0 ref.51.34 ref.32.18 Further research is needed to understand the specific mechanisms by which ocean acidification interacts with other environmental changes and to assess the potential feedback loops that can occur.ref.70.6 ref.51.34 ref.70.6

Impacts of Ocean Acidification on Marine Ecosystems

Ocean acidification has a profound impact on the functioning and productivity of marine ecosystems. It affects a wide range of marine organisms, including calcifying organisms such as mollusks, crustaceans, corals, and some types of algae.ref.75.8 ref.69.3 ref.69.3 These organisms rely on calcium carbonate to build their shells and skeletons, which becomes more difficult in acidic conditions.ref.35.36 ref.35.36 ref.35.39

A meta-analysis of published studies revealed a decrease in calcification, growth, survival, development, and abundance across various taxa in response to ocean acidification. The decrease in calcification rates can lead to weaker structures, making organisms more susceptible to predation and physical disturbances.ref.35.41 ref.34.13 ref.69.3 This can have cascading effects throughout the food web, impacting the abundance and diversity of other species.ref.69.3 ref.69.3 ref.35.39

The impacts of ocean acidification on marine organisms and ecosystems are challenging to predict due to the variability among groups. Some organisms may be more resilient and able to adapt to changing conditions, while others may be more vulnerable.ref.51.34 ref.69.3 ref.69.3 Additionally, the impacts can vary depending on the life stage of the organism and the specific environmental conditions in which they are exposed.ref.32.0 ref.2.31 ref.35.41

The future impact of ocean acidification on marine ecosystems and biodiversity will depend on multiple stressors and the ability of organisms to adapt to rapid changes in ocean pH. The capacity of the ocean to absorb additional CO2 will decline as a result of ocean acidification, and the interplay between counteracting processes makes future predictions challenging.ref.35.41 ref.35.36 ref.32.0 It is therefore crucial to continue monitoring and researching the impacts of ocean acidification on marine ecosystems to better understand and mitigate its effects.ref.35.41 ref.35.36 ref.51.34

Socio-economic Implications of Ocean Acidification

The socio-economic implications of ocean acidification on coastal communities and industries are significant. Coastal communities that rely on marine resources for their livelihoods, such as fisheries and aquaculture, are particularly vulnerable to the impacts of ocean acidification.ref.69.3 ref.70.6 ref.70.28 The loss of marine biodiversity and the degradation of coral reefs can lead to a decrease in fisheries harvests, resulting in economic damages and the loss of jobs.ref.70.29 ref.70.28 ref.70.22

Additionally, factors such as changing locations of dominant ports, social opportunities to benefit from marine resources, and cultural importance can be substantially altered and undervalued. Communities that have traditionally relied on fishing and other marine activities may face significant challenges in adapting to the changing conditions and finding alternative sources of income.ref.66.29 ref.70.22 ref.15.19

It is important to note that the current understanding of the socio-economic implications of ocean acidification is limited. Variables related to fisheries harvest and coral reef coverage provide only coarse proxies for ecosystem services and socioeconomic dependence on marine resources.ref.70.29 ref.70.28 ref.70.29 Further research is needed to fully assess the social-ecological changes and impacts on coastal communities and industries caused by ocean acidification.ref.35.41 ref.70.29 ref.70.7

Mitigating Factors and Processes

While the impacts of ocean acidification are concerning, there are potential mitigating factors and processes that can alleviate its effects. For example, certain species of macroalgae have been found to have the ability to mitigate the negative effects of ocean acidification on bivalve species.ref.69.3 ref.75.8 ref.20.26 These macroalgae can provide a source of food and habitat for bivalves, which can help to buffer them against the impacts of increased acidity.ref.35.39 ref.42.15 ref.69.3

Concrete structures in the ocean can also provide a refuge from ocean acidification for calcifying invertebrates. These structures, such as artificial reefs or submerged breakwaters, can create localized environments with higher pH levels, offering a potential safe haven for marine organisms that are susceptible to the effects of acidification.ref.65.35 ref.23.10 ref.23.8

Seagrass and kelp have also been identified as potential tools for managing ocean acidification. These marine plants have the ability to take up and store carbon dioxide, effectively removing it from the surrounding seawater.ref.65.35 ref.65.15 ref.90.11 By promoting the growth and conservation of seagrass and kelp habitats, we can potentially reduce the impact of ocean acidification on coastal ecosystems.ref.65.35 ref.65.15 ref.22.0

However, it is important to note that the long-term effectiveness and scalability of these mitigation strategies are still being studied. More research is needed to fully understand the potential of these and other mitigation approaches and to develop effective management strategies to minimize the impacts of ocean acidification on marine ecosystems.ref.35.41 ref.90.35 ref.15.8

In conclusion, ocean acidification interacts with other stressors in additive and synergistic ways, resulting in complex impacts on marine ecosystems. The potential feedback loops between ocean acidification and other environmental changes can further exacerbate the effects on marine organisms and ecosystems.ref.70.6 ref.70.7 ref.51.34 The socio-economic implications of ocean acidification are significant, particularly for coastal communities and industries that rely on marine resources. While there are potential mitigating factors and processes that can alleviate the effects of ocean acidification, further research is needed to fully understand their effectiveness and develop comprehensive management strategies.ref.70.7 ref.93.17 ref.69.3 Urgent action to mitigate greenhouse gas emissions is crucial to minimize the potential losses and damages associated with ocean acidification.ref.70.30 ref.70.29 ref.70.30

Monitoring and Modeling Ocean Acidification

Monitoring and Measurement of Ocean Acidification

The current methods and techniques used to monitor and measure ocean acidification involve the establishment of a global moored CO2 network with mooring locations that include pH sensors. The Pacific Marine Environmental Laboratory (PMEL) has been leading this effort since 2003, and they have expanded the network to include pH measurements at 21 of the mooring locations.ref.84.8 ref.84.8 ref.84.7 These moored CO2 and ocean acidification time series are part of a long-term, sustained effort to understand the ocean carbon cycle and its changes over time. The mooring sites include locations in each major ocean basin and a variety of open ocean, coastal, and coral reef environments.ref.84.8 ref.84.8 ref.84.47

The observations used in this study primarily cover the years between 2010 and 2015, with some exceptions. The data collected from these moorings are archived and can be accessed through the Carbon Dioxide Information Analysis Center (CDIAC) and the National Centers for Environmental Information (NCEI).ref.84.8 ref.84.8 ref.84.47 The PMEL ocean carbon mooring data can be found organized by mooring location on the CDIAC website or through the table of PMEL moorings on the NCEI website.ref.84.47 ref.84.8 ref.84.8

Integration of Monitoring Data and Modeling Outputs

To improve the integration of monitoring data and modeling outputs for a better understanding of ocean acidification, it is important to collect values in observational carbon databases and conduct long-term carbon time series measurements. Thorough monitoring of ocean acidification can significantly advance our understanding of this process and its spread throughout Earth's oceans.ref.35.36 ref.35.35 ref.35.49 Additionally, it is crucial to investigate the potential effects of "high CO2-low pH" conditions on the diversity and functioning of marine biota and ecosystems.ref.35.35 ref.35.36 ref.35.36

The interpretation of observed responses should take into account other environmental stressors such as temperature, light availability, oxygen concentration, nutrient concentration, CaCO3 saturation state, and trace metal speciation. Multiple stressor studies over various timescales are necessary to reveal the functional impact of ocean acidification on marine ecosystem services.ref.35.36 ref.65.21 ref.35.41 Furthermore, future modeling approaches should consider the effects of atmospheric and oceanic warming, ocean acidification, and other stressors. The impacts of ocean acidification on marine organisms, especially calcifying organisms, are well-documented, and their vulnerability and potential ecosystem functions should be considered.ref.75.8 ref.35.41 ref.69.3 It is also important to monitor upwelling events, which can negatively affect marine communities and ecosystems.ref.75.8 ref.35.41 ref.75.8

Overall, a comprehensive and integrated approach that combines monitoring data and modeling outputs, while considering multiple stressors, is necessary to enhance our understanding of ocean acidification.ref.35.40 ref.65.21 ref.52.59

Gaps and Limitations in Understanding Ocean Acidification

There are some gaps and limitations in our understanding of ocean acidification due to monitoring and modeling approaches. One limitation is the uncertainty in attributing fossil fuel emissions to changing surface ocean pH, which results in uncertainties of 10% to 15%.ref.70.19 ref.70.7 ref.35.36 Another limitation is the less robust nature of smaller-scale regional signals in different ocean models, which should be interpreted with caution. Additionally, there is a need for thorough monitoring of ocean acidification and collecting values in observational carbon databases to advance our understanding of the process and its spread throughout Earth's oceans.ref.35.36 ref.35.49 ref.35.35 Furthermore, the impacts of ocean acidification on marine ecosystems and climate are not straightforward to predict, and large-scale monitoring is warranted.ref.35.36 ref.70.30 ref.70.7

Limitations of Current Ocean Acidification Models

The available models for predicting future ocean acidification scenarios are reliable to some extent, but they have limitations. The models used in the studies mentioned in the provided document excerpts have shown that present-day ocean acidification already exceeds preindustrial variability in certain regions.ref.35.40 ref.35.41 ref.70.19 However, these global models do not currently resolve coastal processes, which can bias the results when extrapolating to coastal and coral systems.ref.35.40 ref.35.40 ref.70.19

To address this, vulnerability assessments of US shellfisheries have used earth system model output as a baseline for aragonite conditions, but also added a term for amplification of ocean acidification in coastal systems that experience eutrophication, upwelling, and river inputs of low aragonite water. Regional models in coastal systems have also shown promise in predicting surface ocean aragonite conditions.ref.84.39 ref.70.16 ref.70.16

It is important to note that the impact of ocean acidification on marine ecosystems is complex and depends on various factors, including the sensitivity of different organisms and ecosystems to acidification. Some shelled marine organisms have already been impacted by corrosive seawater chemistry conditions.ref.69.3 ref.75.8 ref.69.3 High-frequency moored observations have been effective in capturing the full range of variability at key locations and can help in assessing the impact of ocean acidification on marine life.ref.35.36 ref.35.41 ref.69.3

Overall, while the available models provide valuable insights into future ocean acidification scenarios, they have limitations in resolving coastal processes and capturing the full complexity of ecosystem responses. Further research and observations are needed to improve the accuracy and reliability of these models.ref.35.40 ref.35.35 ref.52.86

Regional and Global Patterns of Ocean Acidification

The regional and global patterns of ocean acidification vary across different oceanic regions. Global models have shown that present-day ocean acidification already exceeds preindustrial variability by a factor of 5 in shallow water tropical Pacific and Atlantic coral reef ecosystems.ref.70.5 ref.70.19 ref.70.5 However, these global models do not resolve coastal processes and lack important sources of natural variability, which affects the extrapolation to coastal and coral systems.ref.70.19 ref.23.8 ref.70.19

Important processes that affect ocean acidification in the coastal ocean include upwelling, riverine/estuarine input, air-sea gas exchange, production and respiration, calcification, dissolution, sediment burial, and sea-ice dynamics. The magnitude and variability of these processes in coastal regions are poorly quantified.ref.75.8 ref.65.41 ref.65.42 Therefore, it can be concluded that the patterns of ocean acidification vary depending on the region and the specific processes occurring in that region.ref.65.44 ref.70.7 ref.70.30

In conclusion, the monitoring and measurement of ocean acidification through a global moored CO2 network with pH sensors provide valuable data for understanding the ocean carbon cycle and its changes over time. Thorough monitoring and long-term carbon time series measurements, in combination with modeling outputs, are essential for a comprehensive understanding of ocean acidification.ref.84.8 ref.35.36 ref.35.49 However, there are gaps and limitations in our understanding, including uncertainties in attributing fossil fuel emissions to changing surface ocean pH and the less robust nature of smaller-scale regional signals. The available models for predicting future ocean acidification scenarios have limitations in resolving coastal processes and capturing the full complexity of ecosystem responses.ref.35.49 ref.35.36 ref.35.49 The regional and global patterns of ocean acidification vary across different oceanic regions, and coastal processes play a significant role in shaping these patterns. Further research and observations are needed to improve the accuracy and reliability of models and to enhance our understanding of the impact of ocean acidification on marine ecosystems.ref.35.36 ref.84.47 ref.84.47

Mitigation and Adaptation Strategies

Mitigation Strategies to Reduce Carbon Dioxide Emissions and Mitigate Ocean Acidification

Mitigating the impacts of carbon dioxide emissions and ocean acidification is crucial for preserving marine ecosystems and ecosystem services. Several potential mitigation strategies have been identified:ref.15.8 ref.15.8 ref.90.29

1. Artificial ocean alkalinization:ref.65.15 ref.90.16 ref.89.35 This strategy involves increasing the total alkalinity (TA) of the ocean by adding alkaline minerals, such as olivine, limestone, or basalt, to the ocean or land surfaces. By doing so, atmospheric carbon dioxide (CO2) can be stored in the ocean as bicarbonate ions (HCO3-).ref.89.35 ref.65.15 ref.89.35 This process helps reduce CO2 levels in the atmosphere and mitigates ocean acidification.ref.90.14 ref.65.15 ref.90.16

2. Renewable energy:ref.90.11 ref.90.16 The widespread implementation of renewable energy sources, such as tidal, wave, and ocean current energy, can significantly reduce greenhouse gas emissions and mitigate the impacts of climate change. These renewable energy sources provide an alternative to fossil fuels, which are major contributors to carbon dioxide emissions.ref.90.16 ref.90.11 ref.90.11

3. Seaweed aquaculture:ref.90.11 ref.99.32 ref.99.32 Large-scale seaweed aquaculture can be used to supplement cattle feed and reduce methane emissions. Methane is a potent greenhouse gas that contributes to climate change.ref.90.11 ref.99.32 ref.99.32 Additionally, seaweed aquaculture can help counteract acidification locally by absorbing carbon dioxide from the water, thereby reducing its concentration and mitigating the impacts of ocean acidification.ref.90.11 ref.99.32 ref.99.32

4. Reduction of other stressors on coral reefs:ref.15.16 ref.15.26 ref.57.40 Local management actions targeting overfishing and pollution can help reduce stressors on coral reefs and increase their resilience to ocean acidification and climate change. Overfishing can disrupt the balance of marine ecosystems and reduce their ability to withstand environmental changes.ref.15.16 ref.23.154 ref.15.16 Pollution, such as nutrient runoff and chemical contamination, can also contribute to the degradation of coral reefs.ref.15.16 ref.15.5 ref.23.154

5. Land-ocean hybrid methods:ref.90.11 ref.90.16 Combining land-based and ocean-based approaches can expand the potential for mitigation. For example, the use of marine biomass for bioenergy with carbon capture and storage (BECCS) can eliminate limitations on terrestrial fuel capacity and expand the storage capacity of carbon dioxide.ref.90.14 ref.90.16 ref.90.14 This approach allows for the capture and storage of carbon dioxide while also producing renewable energy.ref.90.14 ref.90.23 ref.90.11

While these mitigation strategies show promise in reducing carbon dioxide emissions and mitigating ocean acidification, further research and development are needed to assess their effectiveness, costs, and potential trade-offs. It is important to understand the long-term impacts and feasibility of implementing these strategies on a global scale.ref.15.8 ref.35.59 ref.90.11

Innovative Technologies and Approaches for Mitigating Ocean Acidification

In addition to the aforementioned mitigation strategies, there are several innovative technologies and approaches that can help mitigate or adapt to ocean acidification:ref.65.13 ref.65.13 ref.65.13

1. Renewable energy:ref.90.11 ref.90.16 ref.90.26 Renewable energy sources, such as tidal, wave, and ocean current energy, have the potential to address all drivers of ocean acidification. By reducing greenhouse gas emissions, these energy sources help mitigate climate change, which is one of the primary causes of ocean acidification.ref.90.16 ref.90.26 ref.90.26 Implementing renewable energy technologies can contribute to a more sustainable and carbon-neutral energy system.ref.90.11 ref.90.16 ref.90.26

2. Large-scale alkalinization:ref.90.16 ref.65.15 ref.90.16 This approach involves consuming carbon dioxide and neutralizing ocean acidity by storing it as dissolved bicarbonate and carbonate ions or as precipitated calcium carbonate. Large-scale alkalinization has the potential to counteract the acidification of the ocean and restore its pH levels.ref.65.15 ref.90.14 ref.90.16 However, further research is needed to understand the potential environmental impacts and feasibility of implementing this approach.ref.84.3 ref.89.0 ref.90.14

3. Land-ocean hybrid methods:ref.90.11 ref.90.16 Land-based and ocean-based approaches can be combined to expand the mitigation potential. The use of marine biomass for bioenergy with carbon capture and storage (BECCS) is one example of a land-ocean hybrid method.ref.90.14 ref.90.16 ref.90.11 By utilizing marine biomass for bioenergy, carbon dioxide can be captured and stored, thereby reducing greenhouse gas emissions and mitigating ocean acidification.ref.90.14 ref.90.11 ref.90.14

4. Local options for adaptation and valuation of coral reefs:ref.15.16 ref.15.16 ref.15.26 Building adaptive capacity within local communities and industries is essential for dealing with the impacts of ocean acidification and climate change. This can be achieved by improving socio-economic adaptation plans, reducing other stressors on coral reefs (such as overfishing and pollution), and implementing localized and targeted land-based management measures to reduce runoff and sediment.ref.15.16 ref.15.16 ref.15.16 These local adaptation measures can help protect coral reefs and increase their resilience to ocean acidification.ref.15.16 ref.23.10 ref.15.16

The effectiveness of different adaptation strategies in combating the impacts of ocean acidification varies. Strategies such as the management of CO2 chemistry exposure, which involves reducing CO2 emissions and implementing ecosystem restoration or assisted evolution, can be effective in reducing the impacts of ocean acidification.ref.65.13 ref.65.13 ref.65.16 Additionally, the creation of ocean acidification refugia (OAR) can provide localized protection for vulnerable species and ecosystems. OAR can be based on mitigating exposures or enhancing adaptive capacity, depending on the specific ecological context.ref.65.22 ref.65.22 ref.65.14 It is important to note that the potential effectiveness of certain measures, such as alkalinization, cloud brightening, albedo enhancement, and assisted evolution, is still uncertain and requires further research.ref.90.14 ref.90.14 ref.90.14

Local measures, such as protection, reducing pollution, and implementing renewable energy, have high governability and co-benefits, but may have limited effectiveness in moderating climate-related impacts globally. The effectiveness of these strategies also depends on factors such as environmental conditions, species vulnerability, and the persistence of refugia characteristics.ref.90.27 ref.90.33 ref.90.37 Therefore, a combination of different adaptation strategies and careful consideration of multiple criteria, including effectiveness, feasibility, co-benefits, and disbenefits, is necessary to combat the impacts of ocean acidification.ref.90.27 ref.90.26 ref.90.26

Strategies for Enhancing Public Awareness and Engagement

To enhance public awareness and engagement regarding ocean acidification and its potential solutions, several strategies can be implemented:

1. Articulate the value of ecosystem services provided by coral reefs:ref.13.21 ref.15.12 ref.15.11 Global initiatives should emphasize the importance of coral reefs in food provisioning, recreation, culture, and coastal infrastructure protection. By highlighting the benefits that will be lost if coral reef degradation continues, public awareness can be raised, leading to greater support for conservation efforts.ref.15.8 ref.13.19 ref.15.12

2. Strengthen mitigation measures:ref.90.35 ref.15.8 ref.97.32 Mitigation measures, particularly the reduction of greenhouse gas emissions, are crucial in reducing climate change and ocean acidification risks. The Paris Agreement, an international agreement aimed at combating climate change, seeks to enhance global efforts in reducing CO2 emissions.ref.15.8 ref.97.36 ref.97.35 However, current commitments may not be sufficient to reach the agreed targets, and further efforts are needed to strengthen mitigation measures.ref.90.35 ref.90.37 ref.90.35

3. Control sources of pollution:ref.15.8 Addressing pollution from vessels, dumping, and land-based activities can help mitigate harmful damages to the marine environment, including the increase of acidification affecting coral reefs. International agreements and voluntary instruments exist to combat different sources of marine pollution.ref.15.8 ref.15.8 ref.15.16 By implementing and enforcing these agreements, pollution can be reduced, and the impacts of ocean acidification can be mitigated.ref.15.8 ref.15.8 ref.15.8

4. Support adaptive capacity:ref.15.16 ref.15.16 ref.13.20 Building adaptive capacity within local communities and industries is essential for dealing with the impacts of ocean acidification and climate change. This can be achieved by improving socio-economic adaptation plans, reducing other stressors on coral reefs (such as overfishing and pollution), and implementing localized and targeted land-based management measures.ref.15.16 ref.15.16 ref.15.16 By enhancing adaptive capacity, communities and industries can better respond to the challenges posed by ocean acidification.ref.15.16 ref.15.16 ref.23.10

5. Increase public knowledge and awareness:ref.110.3 ref.110.40 ref.110.40 Enhancing public awareness and knowledge about the impacts of climate change on the marine environment is crucial for increasing support for sustainable management. Efforts should focus on providing accurate information, addressing misconceptions, and promoting understanding of the magnitude and rates of change related to ocean acidification.ref.110.40 ref.110.3 ref.90.39 By increasing public knowledge and awareness, individuals can make informed decisions and contribute to the conservation of marine ecosystems.ref.110.3 ref.110.40 ref.110.40

Potential Trade-Offs and Unintended Consequences

It is important to consider the potential trade-offs and unintended consequences associated with different mitigation and adaptation measures. Some of these trade-offs include unintended side effects, negative impacts on farm economy, rebounding vulnerability, shifting vulnerability, eroding sustainable development, and trade-offs between nonclimate and climate policy objectives.ref.105.10 ref.105.23 ref.105.9

For example, the implementation of adaptation measures, such as the use of pesticides and nutrients, establishment of buffer zones, and implementation of new drainage systems, can have unintended side effects on ecosystems. Pesticides and nutrients can contribute to water pollution and harm marine organisms.ref.105.21 ref.105.23 ref.105.21 Buffer zones and drainage systems can alter the natural hydrological processes and disrupt ecosystem functioning. It is crucial to be aware of these trade-offs and consider their severity and additional costs or impacts in decision-making.ref.105.21 ref.105.23 ref.105.16

The integration of adaptation and mitigation strategies in landscape management can help manage these trade-offs and exploit positive interactions. By considering the broader context and interactions between different measures, it is possible to minimize negative trade-offs and maximize co-benefits.ref.103.4 ref.103.28 ref.103.30 Additionally, mainstreaming adaptation and mitigation separately within sectoral policies, such as agriculture and forestry, can be advantageous due to differences in temporal and spatial scales, difficulty in aggregating costs and benefits, and sector-specific relevance.ref.103.30 ref.103.28 ref.103.29

However, there is a need for further research and empirical analysis to better understand the management issues associated with joint adaptation and mitigation and the patterns in practices needed to secure desired outcomes. By considering potential trade-offs and unintended consequences, decision-makers can make informed choices and implement strategies that effectively address the impacts of ocean acidification while minimizing negative impacts on other aspects of the environment and society.ref.65.23 ref.90.35 ref.90.39

Works Cited