Fig. 1 seagrass meadow [source]
What is ocean acidification?
Fig. 2 ocean acidification [source]
Of all the carbon dioxide (CO2) we release into the atmosphere, around 25% is taken up by the oceans where it interacts with seawater and forms carbonic acid in a phenomenon called ocean acidification (“Ocean acidification”). Ocean acidification is the ongoing decrease in the pH value (getting more acidic) of the Earth's oceans. This happens due to interactions with surrounding rock (particularly carbonate forms) and other materials, precipitation of acid rain, and wastewater or mining discharges. In addition, the oceans’ pH levels can change from the direct uptake of CO2 from the atmosphere (“pH of Water”). Globally, the oceans’ pH has dropped from 8.2 to 8.1 and could drop another 0.4 units by the end of the century. It is then perhaps unsurprising that dead zones are rising at an alarming rate, from 400 in 2018 to 700 in 2019. Over 3 billion people rely on the oceans for their livelihoods (“Goal 14”), and more than 4.5 billion people obtain at least 15% of their animal protein intake from fish (“Ocean acidification”). Ocean acidification affects the amount of available seafood, as well as the nutritional qualities of seafood. When water’s pH drops and gets more acidic, fish's cells often adapt to the seawater by taking in carbonic acid. This changes the pH of the fish's blood through acidosis, making the fish ill or even die. Ocean acidification can also modify the abundance and chemical composition of harmful algal blooms. These algae are food to shellfish, so their natural toxins accumulate in shellfish, and this may in turn negatively affect human health. Ocean acidification has been found to lead to an increased algal growth rate, a change that could accelerate the production of toxic algae. Moreover, the toxicity of the blooms is likely to increase. These toxins not only enter the human body through food but also through the air. Exposure to high concentrations of H2CO3 can irritate the respiratory tract and the eyes (“Carbonic Acid”).
How does seagrass solve the problem?
Fig. 3 marine life protectors [source]
Seagrass can effectively absorb CO2 and reduce acidity in the ocean. Growing these plants in local waters, scientists say, could help mitigate the damaging impacts of acidification on marine life (Jones). Seagrasses, like other plants, have chloroplasts that produce food for themselves. Chloroplasts use energy from the sun to convert carbon dioxide and water into sugar and oxygen for growth, through a process called photosynthesis. Photosynthesis in a scientific equation is 6CO2 (carbon dioxide) + 6H2O (water) + sunlight → C6H12O6 (glucose) + 6O2 (oxygen). Through this process, seagrass turns CO2 into O2, reducing acidification and neutralizing water to levels that are more favorable for aquatic life to grow (6.5 to 8.5). Seagrasses are very pervasive and efficient at sucking up carbon. One study said seagrass meadows should give corals about an 18% boost in growth. This scientific solution is related to UN SDGs 3 (Good Health and Wellbeing), 6 (Clean Water and Sanitation), and 14 (Life Below Water). It helps reach targets 3.9 and 6.3 by reducing ocean acidification, a type of water pollution, and ultimately preventing toxic nutrients and excessive carbonic acids from entering the human body. The solution also contributes to attaining targets 14.1, 14.2, 14.3, and 14.5 by conserving marine and coastal ecosystems from ocean acidification using science.
Advantages of using seagrass as a solution
Fig. 5 seagrass plantation [source]
The first advantage of this solution is that it is small-scale yet efficient and sustainable, compared to grander schemes like geo-engineering. The implementation requires only the planting of seagrass on seabeds, and the planted seagrass expands in size by itself because it is pervasive (Jones). Once seagrass is planted, its photosynthesis occurs consistently in the marine environment. Seagrasses are thus known as the "lungs of the sea." One square meter of seagrass can generate 10 liters of oxygen every day through photosynthesis (Reynolds). The only barriers to their photosynthesis are the exacerbation of water conditions such as reduction in water clarity, both from increased nutrient loading and increased turbidity. Luckily, seagrasses also slow the flow of water, capturing sand, dirt, and silt particles. Their roots trap and stabilize the sediment, which not only helps improve water clarity and quality but also reduces erosion and buffers coastlines against storms. Therefore, seagrass can be seen as a sustainable solution to ocean acidification (Reynolds).
Fig. 6 seagrass protecting marine life [source]
In addition, seagrass is vital for marine life, which depends on the meadows for food and shelter. A 10,000m2 area of seagrass can support 80,000 fish and over a million invertebrates (“Planting hope”). Birds and aquatic mammals like nutria can also feed on seagrass, taking carbon dioxide back to land with them. When those animals are eaten or die, they transfer carbon and nutrients from seagrass into terrestrial habitats. Fish also move seagrass nutrients around through feeding and migration to offshore environments (MacDonald). As such, seagrass cooperates with marine life to provide a nursery and create a carbon cycle. Contrasting some unnatural methods like geo-engineering and throwing metals that absorb CO2 into the ocean, this solution does not risk the unpredictable shift in food webs.
Limitations of using seagrass as a solution
While many advantages of using seagrass to combat ocean acidification exist, there are still limitations. First, many scientists do not yet know about the effect of seagrasses on ocean chemistry. Some breeds, like the invasive Zostera japonica eelgrass, tend to shed their leaves in the winter, and the degrading plant matter boosts carbon dioxide levels in the water rather than lowering them (Jones). These invasive seagrass species suppress native seagrasses, reduce coastal protection, and decrease biodiversity. The rapid expansion of these invasive species would create huge aftermaths. To troubleshoot these repercussions, more research needs to be done on the safety of implementing seagrasses to tackle ocean acidification. This would take more time, causing ocean acidification to continue.
Fig. 7 seagrass photosynthesis and cellular respiration [source]
Furthermore, seagrass’s absorption of CO2 and production of O2 depend on sunlight, which is a requirement for photosynthesis. CO2 is not released during photosynthesis, but small amounts of it are emitted both day and night as a by-product of cellular respiration (Petruzzello). During the night, there is no sunlight, so photosynthesis stops, and respiration predominantly occurs: plants consume O2 and produce CO2. As such, seagrasses do the reverse effect of their role as a solution to ocean acidification at night.
So should we use seagrass to combat ocean acidification?
The analysis above proves that we can be fairly hopeful that seagrasses will help solve ocean acidification. Although this solution is not perfect, it is sustainable and provides additional advantages to the marine ecosystems such as being a nursery for endangered wildlife. The limitation of seagrasses’ respiration at night is trivial, considering how seagrasses absorb carbon dioxide during the day for photosynthesis and do so in greater amounts than they release for cellular respiration. Compared to grander schemes like geo-engineering, seagrass planting is done on a much smaller scale, making implementation more efficient. Seagrasses’ photosynthesis is a well-known process that will definitely decrease CO2 from the oceans. However, it would be ideal to have another solution accompany this one to accelerate the solution to ocean acidification.
MLA Citations
“Carbonic Acid (H2CO3) - Structure, Properties, Preparation, Uses, and FAQs of Carbonic Acid.” BYJU’S, https://byjus.com/chemistry/carbonic-acid/.
“Goal 3 | Department of Economic and Social Affairs.” UN SDGs, https://sdgs.un.org/goals/goal14.
“Goal 6 | Department of Economic and Social Affairs.” UN SDGs, https://sdgs.un.org/goals/goal14.
“Goal 14 | Department of Economic and Social Affairs.” UN SDGs, https://sdgs.un.org/goals/goal14.
James MacDonald. “Why We Need Seagrass.” JSTOR Daily, 25 June 2018, https://daily.jstor.org/why-we-need-seagrass/.
Knowlton, Nancy. “Seagrass and Seagrass Beds.” Smithsonian Ocean, 30 Apr. 2018, https://ocean.si.edu/ocean-life/plants-algae/seagrass-and-seagrass-beds.
Nicola Jones. “How Growing Sea Plants Can Help Slow Ocean Acidification.” Yale E360, 12 July 2016, https://e360.yale.edu/features/kelp_seagrass_slow_ocean_acidification_netarts.
Petruzzello, Melissa. “Do Plants Emit Oxygen and Carbon Dioxide at Night?” Encyclopedia Britannica, https://www.britannica.com/story/do-plants-emit-oxygen-and-carbon-dioxide-at-night.
“PH of Water - Environmental Measurement Systems.” Environmental Measurement Systems, 10 June 2022, https://www.fondriest.com/environmental-measurements/parameters/water-quality/ph/.
“Planting Hope - How Seagrass Can Tackle Climate Change.” WWF, 10 June 2022, https://www.wwf.org.uk/what-we-do/planting-hope-how-seagrass-can-tackle-climate-change.