Our oceans are the Earth's circulatory system. Protecting them from climate change protects us all. However, oceans are under threat. Part of that threat is ocean acidification. This is seldom talked about but is every bit as much of a threat as warming temperatures.
Marine ecosystems sequester carbon by storing it in their bodies or by dropping it into the deep sea to fertilize and protect marine plants. For example, one study in 2018 estimated that in the Abu Dhabi area, marine mammals, sea turtles, and seabirds store 520 tonnes of carbon as living biomass. These "blue" carbon stores are important, but climate change is causing increasing challenges for marine life, whether it is tiny snails or giant whales. Reducing your carbon footprint helps, but so does understanding what is going on in our oceans and the threat to marine life.
Understanding ocean acidification means understanding some basic chemistry. Liquids are acidic if they have a low pH and alkaline if they have a high one. The middle of the scale is neutral, pH 7. Anything above 7 is considered a base or alkaline, while anything below 7 is considered an acid. Currently, the average pH of the ocean is 8.1, making it basic. However, dissolved CO2 lowers the pH of the water. As it dissolves, it creates carbonic acid (H2CO3), which then breaks down into hydrogen ions (H+) and bicarbonate ions (HCO3-). The basic explanation is that the more CO2 dissolves into the oceans, the more acidic they become.
As we add more CO2 to the atmosphere, the ocean becomes more acidic. Unfortunately, marine life has evolved to exist in a basic environment, so as the ocean becomes acidic, they start to have problems. This then reduces the amount of carbon in blue stores and accelerates the cycle. Slowing ocean acidification reduces this impact and helps control the climate.
Ocean acidification can also be caused by excessive nutrients and certain pollutants, with agricultural fertilizers being a major culprit. Coastal erosion may introduce more fertilizer into the ocean. This creates local acidification hotspots that can be a major problem for marine life. Coastal pH can vary substantially, and when local hot spots are added to the global issue, it can cause literal dead zones in marine ecosystems.
Again, marine life evolved in oceans that have a certain pH. As that changes, they start to face significant issues. The biggest threats are to:
You have probably heard about bleaching events, which are caused when coral's algae symbiotes leave or die, leaving the coral white and highly stressed. Bleached corals can recover, but they are extremely vulnerable to other threats.
One of those threats is acidification. Coral reefs grow by producing calcium carbonate (limestone). While the coral itself is alive, its skeleton is essentially made of rock. This rock can erode. So, if a reef is not producing limestone faster than it is eroded, the reef can't grow and may even start to shrink. This calcium carbonate is pulled out of the ocean, but as the ocean becomes more acidic, there are fewer available carbonate ions, which bond with hydrogen in the water. The coral doesn't have anything to build with, and if the ocean becomes acidic enough, the reef may even start to dissolve.
This then impacts all of the creatures that live in and around coral reefs, which have the highest biodiversity in the ocean. Reefs are also vital for protecting low-lying tropical coastlines from storms, providing food and medicine to humans, attracting tourists, and being culturally important to indigenous peoples. Over half a billion people directly rely on reefs, whether it's for food or tourism income. The loss of reefs would impact fisheries all over the world and significantly reduce the world's biodiversity.
Shellfish also rely on calcium carbonate in the ocean to build their shells. Species such as oysters and clams experience shell dissolution if the pH gets too low, with the calcium being leached out of their shells. Shellfish are important food for humans and aquatic animals alike.
One key species is the pteropod, a tiny sea snail that is consumed by everything from krill to whales (who also, of course, eat the krill). Researchers have found serious levels of shell dissolution in the southern ocean.
Shellfish growers are already facing significant economic losses. Hatcheries are able to compensate by adding sodium carbonate and planting eelgrass, but this strategy isn't going to work forever. This impacts the culture in many parts of the world. Even hermit crabs, who claim the shells of others, are experiencing problems...there are simply fewer good-quality shells for them to use.
We've already talked about the pteropod, a key part of the food chain that goes all the way up from plankton to the ocean's largest creature, the blue whale. These tiny creatures are a major food for juvenile Pacific salmon, as well as other fish of value to humans. But acidification disrupts food chains all over the place. For example, some oyster hatcheries have lost 80% of their production.
But it's not just about shells. For example, phytoplankton feeds fish and whales and provides fatty acids. Higher CO2 concentrations have been shown to reduce the polyunsaturated fatty acid (PUFA) content of certain phytoplankton. Essentially, this makes the phytoplankton less nutritious for the animals that depend on it. This goes up the chain by reducing the growth of zooplankton, resulting in less food available for ocean grazers. (A side issue is that ocean acidification may make shrimp taste bitter). The changes might also cause a phytoplankton shift towards larger species, which reduces the abundance of sea urchins. In other words, it can tug on the entire web, having impacts that may be hard to predict or understand ahead of time.
Whales, seals, and seabirds all depend on this food chain to survive. While ocean acidification might not affect whales and dolphins directly, it reduces the amount of food available to them, limiting their ability to survive and breed. If we want there to still be whales, seals, etc, in our oceans, we need to take steps to reduce ocean acidification and the food chain disruption it causes.
We've already mentioned the vital importance of blue carbon stores as a sink. The carbon cycle in the oceans is vitally important, but ocean acidification can impact it in a number of ways. Currently, the ocean absorbs about 30 percent of the carbon released into the atmosphere. However, as temperature increases, water absorbs less carbon dioxide, and warmer areas may start to release carbon instead of absorbing it, creating a feedback cycle.
But where the real consequences lie are in the same impacts on marine life. Fewer whales mean fewer whalefalls and, thus, less carbon being sequestered in the ocean. As food webs collapse, ocean life dies and becomes less useful as a carbon sink. This will then cause the temperature to rise further, further acidifying the oceans and continuing to degrade their ability to absorb carbon.
This will then cause atmospheric carbon levels to increase further. If the oceans were not in the loop, then we would already be seeing climate impacts that might make parts of the planet unlivable.
In the U.S., research into ocean acidification is being conducted by the National Oceanic and Atmospheric Administration (NOAA). Specifically, the PMEL Carbon Program focuses on large-scale observations of ocean interior carbon and surface ocean carbon. They use ships and buoys to monitor pH and pCO2 levels to help keep track of ocean acidification and damage to the oceans caused by elevated carbon levels. An important part of this is volunteer observing ships, primarily cargo ships, which the program employs to monitor the oceans while they go about their normal business.
The Ocean Foundation is also involved in doing research on ocean acidification and marine ecosystems. Their goal is to help smaller countries develop their own monitoring and mitigation strategies. A lot of research is being done, with more and more information coming out about just how much acidification can affect biosystems and fisheries.
Knowing we have a problem is the first step towards resolving that problem. Mitigating ocean acidification will help preserve fisheries and keep the ocean able to act as a carbon sink in the future. There are a variety of things that can be done, which include:
Anything we do to reduce CO2 emissions also mitigates ocean acidification. The more carbon in the atmosphere, the harder the oceans and ecosystems have to work to sequester carbon, and the lower their ability to do so becomes.
Our first priority needs to be to cut emissions and reduce our carbon footprint as much as possible. Transferring to green sources of energy is key to mitigating all impacts of climate change.
Solar power is part of our energy future and very much part of the solution. Community solar helps everyone, including renters, save on their electricity costs, do their bit to reduce emissions and help the environment.
As ocean systems become more stressed, overfishing becomes more of a problem. Marine reserves support fisheries by providing protected areas where fish can spawn, as well as protecting more sedentary fish and important habitats.
Aquaculture farms can help bring local pH back up by planting and farming seaweed. While seaweed is not a popular food in the West, it is consumed in many parts of Asia. A pilot project in California showed that native seaweed can alleviate the effects of local acidification while providing another source of food for humans and animals. Feeding seaweed to cows has the beneficial side effect of reducing methane emissions from cattle, another source of greenhouse gas.
Growing seaweed around oysters and other shellfish hatcheries can help reduce the stress on them caused by acidification.
Sustainable fisheries provide food for humans but also help mitigate climate change and related problems, including ocean acidification. Planning fisheries and hatcheries to actually raise the local pH through growing seaweed can make a huge difference to the biosphere and the local economy.
While ocean acidification is a global problem, it is one that can be impacted at the local level. Local initiatives to raise ocean pH have already been mentioned, such as growing seaweed in California.
Some examples of local initiatives include:
Wetland restoration can also help with ocean acidification by reducing runoff from agriculture, as can initiatives to reduce the overall use of fertilizer.
It's easy to feel overwhelmed by climate-related issues. Many of us are left feeling as if the scale is too big, and there's nothing we can do. However, there are things individuals can do to reduce the impact of ocean acidification. These include:
While an individual carbon footprint is small, they add up. Consider the following actions:
You can also do your part to reduce runoff by using less fertilizer in your yard, planting native vegetation at the edge of your property, or putting out a rain barrel to reduce runoff and save water...you can use the water to water your garden or lawn. Additionally, if buying fish or shellfish, make sure it is sustainably sourced. Consider adding seaweed to your diet to encourage farming it and to help out shellfish farmers who are using it to protect hatcheries.
Look for global or local marine conservation organizations and give them your support, whether it's through cash or volunteer time. There are a variety of organizations that do everything from studying invasive species to restoring wetlands to protecting and preserving reefs. Your local organizations might organize beach clean-ups or other events where you can help marine life. Helping with other stressors can help biosystems handle acidification better.
Local organizations also know and understand local concerns. If you live in an area with fisheries, you can also find out from fishermen what they need and push organizations to help them. Sustainable fishing really does help marine ecosystems as well as providing food for millions of people.
At this point, pretty much everyone knows climate change is a thing. Not everyone understands or knows about ocean acidification. Spreading awareness and encouraging other people to do their thing is something we can all do.
The 8th of January is the Ocean Acidification Day of Action. Share the website with your friends and look for local and online events to "celebrate" the day. Use their social media toolkit. You can also watch ocean-related videos and documentaries. But you can share resources online throughout the year.
Another way to spread awareness might be to serve seaweed and seaweed products to your friends or bring them to a potluck. If you are doing a fish fry, you can also use that as an opportunity to tell people about the potential risk to fisheries.
It doesn't take much to help people learn about ocean acidification and what they can do to prevent it or how reducing their carbon footprint can help support the health of Earth's oceans.
Ocean acidification presents a real threat to marine ecosystems worldwide, especially to shellfish hatcheries and coral reefs. Many of us are dependent on protein from the ocean as our primary source. Protecting the ocean requires immediate action, and that primarily takes the form of reducing carbon emissions. Steps to reduce local runoff, such as fertilizer, are also helpful.
Individuals can help by saving energy, purchasing fish and shellfish from sustainable sources, supporting conservation organizations, and spreading awareness. Getting involved in conservation efforts both helps the ocean and your mental health. Moving forward, we all need to do our bit to reduce ocean acidification and take steps to protect the oceans and the animals within them.