Restoring our Reefs: How Climate Adaptation and Coral Gardening are Mitigating Ocean Acidification

Thea Pratt

7 days ago

6 min read

Commonly known for their natural beauty, coral reefs are some of the most environmentally and biologically diverse ecosystems in the world. While they cover less than 1% of earth’s ocean floor, they provide habitat and support for a staggering 25% of all marine life, offering biomes, nurseries, and hunting grounds for over a million species. Their location near beach shores and their rigid structure allow for them to break wave impact and prevent substantial shoreline erosion. So not only are they visually appealing, the settings of various tourism destinations, they also are a backbone of our oceans.

However, due to the increasing consequences of climate change, our corals are taking the brunt of its effects. Despite popular belief that rising ocean temperatures are the primary culprit of coral reef death, the real killer is chemical acidification. Our oceans absorb nearly 30% of carbon dioxide (CO2) gas emissions, a trait crucial to our planet's biological health. But even nature's most powerful force, the sea, cannot stay unaffected from the harsh effects of climate change. Because of increasing carbon dioxide in the climate, seawater is becoming increasingly acidic, harming coral reefs worldwide and damaging their ability to thrive.

What is Ocean Acidification?

The best way to understand why acidification is so harmful to coral reefs, is to investigate the chemical science of the process. Ocean acidification is a process that results from the absorption of atmospheric CO2 by the world’s oceans. Approximately 150 billion metric tons of the CO2 emitted into the atmosphere by human activities is absorbed by the ocean each year. These human activities include deforestation, transportation, and burning fossil fuels in order to produce energy.

Once dissolved in seawater, carbon dioxide undergoes a chemical reaction to form carbonic acid (H2CO3), which then dissolves into hydrogen ions (H⁺) and bicarbonate ions (HCO3-). The increase in H⁺ ions lowers the pH of seawater, making it more acidic.

Historically, the average ocean pH has remained relatively stable at around 8.2. However, it has dropped to an 8.1 since the Industrial Revolution, demonstrating a 30% increase in acidity. While this drop of 0.1 might seem trivial, it profoundly affects marine biochemical processes and ecosystems. Taking account of this trend of acidification, scientists are predicting that if CO2 emissions continue at the harmful rate they’re going, the ocean’s pH could drop by multiple units by the end of the century and so on, raising disastrous concerns about its implications for marine life.

How is Ocean Acidification Affecting Coral Reefs?

So we now understand how ocean acidification is harmful to marine life as a whole, but how does it specifically target and damage our coral reefs? The majority of today’s reefs belong to a marine group called Scleractinia, which refers to hard corals. Their structure comprises a hard exoskeleton, made of a solidified calcium carbonate, also known as aragonite. Calcium carbonate, formed through the coral's absorption of calcium and carbonate ions in the water, is a mandatory compound in the construction of the coral structure.

However, as acidification of the ocean continues, and there is more hydrogen in the water, those excess H⁺ ions react with carbonate ions to form bicarbonate instead. This effectively utilizes the majority of the carbonate that coral reefs need to facilitate their growth. As there are fewer carbonate ions, coral reefs end up having to use significantly more energy to survive and maintain their structures.

This process also results in lower skeletal density, making reefs more prone to destruction and erosion. Additionally, in extreme acidity, coral can become unsaturated of calcium carbonate, causing them to fully dissolve. So combined with ocean warming, which causes coral bleaching, ocean acidification is virtually killing a marine habitat that is a necessity for biodiversity.

Who is Trying to Mitigate This Problem and How?

While ocean acidification is rarely covered in the news, there are organizations that are willing to protect our coral reefs. One such organization, Coral Gardners, has joined the fight. As an international ocean restoration organization, The Coral Gardeners began their inspiring work in 2017, focusing on the Tuamotu Archipelago in The South Pacific. They realized that simply designating areas as Marine Protected Areas (MPA’s), was not enough and decided to physically rehabilitate and plant healthy coral reefs back into the sea floor.

So how are the Coral Gardeners actually rehabilitating the reefs? Since their founding, The Coral Gardeners have successfully planted over 100,870 super corals, a type of coral that can survive extreme stress, including acidic ocean conditions. Once these super corals have been found, The Gardeners microfragment a piece of the coral in order to trigger a rapid healing response, resulting in increased rates of biological recovery. The coral cells detect injury to their structure and activate rapid cell division and tissue formation for survival, increasing its healing rate by nearly 25%. Then, these fragments are placed on an underwater rope in sheltered ocean nurseries until they reach maturity. Finally, once the coral is fully grown, divers fuse the newly made structures to preexisting coral reefs to fully propagate them into their new environment.

To further their efforts in maintaining a healthy reef structure, The Coral Gardeners also created a sensor network called ReefOS. ReefOS allows the team to access underwater imaging, ecological recovery and detect signs of coral reef degradation. With more than 29 coral reef species being successfully propagated in French Polenysia. The average rates of survival for those young coral nurseries were recorded at a staggering 93.5%. The ReefOS stationed in the nurseries in Tuamotu Archipelago recorded growth over 19x larger than the initial volume planted. Similarly, their nursery in Fiji demonstrated a 25x growth than its initial measurements.

The Coral Gardeners are no doubt an inspiring organization to all those concerned with marine conservation. Although coral reef propagation is not a cut and dry solution in the fight against ocean acidification, it does grant us some much needed time to garner more global support for the cause. With hope that in the future, this issue will be a concern to the entire population.

What can you do to help?

Given the widespread impacts of climate change and the outsize impacts that corporations have on global warming, it’s difficult to feel that we as individuals can have an impact. This is not the case. Even the smallest of actions add up to help reduce climate change-driven consequences. For example, the Coral Gardeners offer an, ‘Adopt a Coral’ opportunity in which you can choose a number of coral to donate to. The money will help fund supplies for the gardens and facilitate even more coral reef regrowth. There are also many ocean related solutions that don’t require donation. Take, for example, switching to reef-safe sunscreen that doesn't contain harmful chemicals. Chemical changes in coral reefs don't just come from ocean acidification, but also your skincare… Sunscreen containing ingredients like oxybenzone and octinoxate are extremely damaging to coral structures, cause wide-spread bleaching and are best to avoid.

While taking measures to ensure personal environmental consciousness is necessary, one of the key ways to prompt change is to take your fight to a systemic level. Public action is incredibly influential in advocating for federal science funding. There are several different campaigns, national and international, which focus heavily on funding environmental enforcements that you can engage with. The Restoring Resilient Reefs Act, a bipartisan federal law signed in 2022, that funds the bulk of the National Oceanic and Atmospheric Administration's (NOAA) Coral Reef Program. Lobbying your local congressional leaders to fully fund the NOAA program is much more helpful than you’d think! Writing to legislators, asking for their support in funding the program is a great way to start, as it needs sufficient amounts of financing to maintain its utility. Additionally, joining campaigns like the Surfrider Foundation, a coastal management coalition, is equally as impactful. Through signing active campaigns, like Surfriders Ocean Protective Initiatives actually helps demand the expansion of Marine Protected Areas!

Ultimately, coral gardening cannot single handedly prevent dying reefs. Supporting candidates and local initiatives that prioritize coastal protection, marine health and carbon emission reduction is one of the strongest ways to protect our oceans' health. Preserving marine biodiversity and reef centered ecosystems is extremely important, and by even attempting to do some of the listed actions, is helpful. Take it one step at a time, or in the Coral Gardener’s case, one coral at a time!