By Natalie Burnett
The acidification of our oceans has been increasing for over two centuries and continues to grow at a rate far greater than ever witnessed before.
The implications of this on marine life are detrimental, specifically to those with carbonate shells or skeletons that are more susceptible to the corrosive nature of acidifying oceans. In 2017, UNESCO predicted that if the acidity of our oceans continues to increase as it is, the coral reefs present in all 29 reef-containing world heritage sites will no longer exist as functioning coral reef ecosystems by the end of the century. But what is causing this terrifying change in our oceans, and is there anything we can do to stop it?
Ocean acidification and its causes
It is no surprise that ocean acidification is often described as climate change’s evil twin. Atmospheric CO2 dissolves into the ocean, reducing the pH and increasing acidity. The pH scale is used to measure how acidic or alkaline a substance is, with zero being the most acidic, fourteen the most alkali, and seven being neutral. CO2 has been exchanged between atmosphere and ocean for thousands of years; however, humans began to disrupt this naturally occurring process over two centuries ago, when the industrial revolution began. Since then, 400 billion tonnes of CO2 have been pumped into the earth’s atmosphere. With the oceans absorbing as much as 30% of the carbon dioxide released into the atmosphere, this extra CO2 has caused a 0.1 drop in the pH of the ocean since the 18th century. While this may not seem like much, in evolutionary terms it is a blink of an eye, representing a 28% increase in ocean acidity. In the past the pH of the ocean has been known to fluctuate by 0.2 pH during colder and warmer stages of the planet’s existence, but this was a change that occurred over tens of thousands of years. Now, marine life cannot keep up with the pace of change that the ocean is currently undergoing.
The pH of the ocean is projected to fall from 8.1 to 7.8 by 2100, a 150% increase on today’s already alarming acidity levels if we continue on a ‘business as usual’ path. One of the primary culprits of CO2 emissions has been the burning of fossil fuels like coal, natural gas, and oil. The Intergovernmental Panel on Climate Change (IPCC) found in 2018 that 89% of global CO2 emissions came from fossil fuels and industrial processes such as cement production, which alone contributes to about 8% of the world’s CO2 emissions. Land use, land-use change and forestry (LULUCF) including deforestation is another major contributor to increased atmospheric CO2, responsible for just under 25% of global CO2 emissions. When trees are cut down, the CO2 stored as carbon within them and the soil is released. As a consequence of the increased CO2 emissions since the industrial revolution, the ocean is absorbing more CO2, resulting in its increasing acidity.
Effects on marine life
Ocean acidification has a particularly detrimental impact on organisms who have calcium carbonate shells or skeletal structures. Carbon dioxide dissolved in the ocean combines with water to form carbonic acid, which then breaks into hydrogen ions and bicarbonate ions. These excess hydrogen ions cause the increased acidity of the ocean, but also bond with available carbonate ions. This reduces the number of carbonate ions available for the building and maintenance of calcium carbonate shells that many marine organisms rely on for survival. With excess hydrogen ions creating conditions that are no longer optimal for the bodily functions of many organisms such as mussels, sea urchins, and crabs, more energy is used to maintain healthy body fluid chemistry rather than growing critical body parts like their shells, causing their protective layers to dissolve.
Perhaps the most famous victims of ocean acidification are coral reefs, who rely heavily on the ocean’s alkaline conditions, not just for their calcium carbonate shells, but also their mutualistic relationship with algae that they depend on for survival. The coral provides shelter for the algae, and both provide the other with the nutrients needed to live. Warming waters are causing the coral to expel these algae, a process known as coral bleaching. Not only does this make corals more vulnerable to disease, but also less able to maintain and build their calcium carbonate skeleton. Recovering from these bleaching events is made almost impossible by the lack of carbonate ions available due to ocean acidification. With ocean acidity and warmth predicted to increase by 86% by 2050, it is unsurprising that very few warm water reefs will still exist in the near future. According to a recent IPCC report, if average global temperatures rise 2°C above pre-industrial levels, 99% of the worlds warm-water reefs will disappear.
Many of the species reliant on calcium carbonate for their shells and skeletons constitute the bottom of the food chain. With the reduction in carbonate availability significantly reducing chances of their offspring surviving, this will have massive implications for the marine food web.
The economic impacts are enormous
It is unsurprising that the effects of ocean acidification are having huge impacts on shellfish fisheries across the world. Along the Pacific Coast, for example, there has been a huge reduction in the Dungeness crab population, the highest-revenue fishery in Oregon and Washington states. Northwest fisheries in America have already experienced multimillion-dollar losses to local economies due to the rapid increase of toxic algal blooms caused by ocean warming that are infecting shellfish and pose a risk to human health. These toxic algae are also responsible for the death of other sea creatures such as the Florida Manatee. This has forced many fisheries in the west coast to shut down. With the increasing acidification of oceans, fisheries are only likely to face more challenges in the future. Fisheries also rely tremendously on coral reefs due to the huge diversity of marine life that they inhabit. The National Marine Fisheries Service estimates that the commercial value of US fisheries from coral reefs is over $100 million. Coral reefs also have huge economic benefits through tourism and recreation. In Australia, the Great Barrier Reef made an economic contribution of $6.4 billion, as well as supporting 64,000 jobs. As coral reefs are destroyed, they lose their value as a tourist destination, which could cause huge damage to economies that rely on the reefs to support them.
Currently the most effective way to prevent the continued acidification of oceans is to reduce atmospheric CO2, in turn reducing the amount that is absorbed into our oceans. Therefore, if we wish to prevent the death of our oceans, we must dramatically reduce global CO2 emissions. If we act now, we could avoid drastic declines in fish catch potential, saving many fisheries and rescuing 30% of coral reefs from extinction. Ocean acidification is the evil twin of climate change, like Bonnie and Clyde, one cannot perform without the other and both create havoc wherever they are found. We can be certain that without drastic action the implications of climate change will be devastating to life under the ocean.
Graphic courtesy of Alice Eaves