Beyond just causing global warming, increased CO2 emissions pose a serious threat to the future of marine life. Increased amounts of CO2 in the atmosphere combine with seawater to form carbonic acid, a weak acid that lowers the pH of the water, causing ocean acidification. This environment interferes with coral growth and makes it more difficult for animals like mussels and clams to grow strong shells. Any changes in oceanic life threatens the food chain and could potentially cause species extinction if ocean acidification isn’t combatted.
While ocean acidification itself is a problem, the truly concerning thing is the rapid rate at which this acidification is occurring. In the past 15 years, the pH of oceans has decreased by an average of 0.12 units. Because the pH scale is logarithmic, this represents a 30% increase in ocean acidity. The last time the ocean’s pH changed so significantly was over 250 million years ago. At this time, increased volcanic eruptions raised CO2 levels. This ultimately led to the world’s biggest mass extinction, in which 90% of oceanic life died off.
The ocean is divided into layers, and the top layer is the most acidic because it directly absorbs CO2. Wind mixes the water around, which acidifies deeper oceanic layers somewhat. The top sunlight-receiving layer of the ocean is home to photosynthesizing single-celled phytoplankton, which are at the bottom of the oceanic food chain. Small crustaceans called zooplankton consume phytoplankton. Fish then consume the zooplankton, and the food chain continues. At night, small crustaceans called copepods rise up from deeper layers of the ocean to consume zooplankton. They return to the deep ocean during the day, where they are a food source for bigger organisms. However, the acidifying ocean means that they travel through a variety of unexpectedly low pH zones. Though the deep ocean’s pH is decreasing minimally, the organisms living in it are used to a fairly constant environment, so these small changes are significant to them.
As a result of ocean acidification, all marine life has to spend more energy regulating internal pH. As their tissues and fluids become more acidic, many organisms minimize pH changes through buffer systems, in which weakly basic molecules, such as bicarbonate ions, react with the hydronium ions, preventing their internal pH from staying so low. Many organisms have to pump hydronium ions in and out of cells accordingly, and others temporarily lower their metabolisms. All of these are temporary fixes that prevent organisms from using energy for other essential processes, like protein synthesis. If ocean acidification had occurred slowly, like over tens of thousands of years, marine life may have been better able to adapt to the conditions, leading to organisms with higher quantities of buffer molecules. But over hundreds of years, adaptation is unlikely to occur fast enough. This could mean death for many marine organisms, especially those who have small quantities of buffer molecules.
Studies have shown that increased energy expenditure to regulate pH has significant negative consequences. The sperm of one Australian sea urchin, Heliocidaris erythrogramma, showed significant decreases in overall movement and speed when they were placed in seawater with a pH lowered by 0.4 units, which resembles potential oceanic conditions in 2100. Because sea urchin sperm survive for a short time, this led to a 25% decrease in effective fertilization, showing that the more acidic environment could decrease adult sea urchin populations. Other organisms like snails, brittlestars, and conches also suffer when it comes to growth and development, according to other studies. Acidification can also inhibit iron absorption in some phytoplankton, which is essential for their growth. Phytoplankton are a critical part of the food chain and produce oxygen that people breathe, so these conditions could have widespread effects. Other species, like copepods, simply die in more acidic conditions. Ultimately, all marine life is put under increased stress by ocean acidification.
Combatting ocean acidification requires increasing global action against climate change. Experts recommend setting a target for the pH to lower no more than 0.1 units in the next century. Keeping atmospheric CO2 levels at a maximum of 350 ppm is the safest to protect coral reefs and organisms with shells. If the U.S. Environmental Protection Agency categorizes CO2 as a pollutant under the Clean Water Act, then CO2 emissions limits can be legally enforced by states. At the same time, more ocean acidification research needs to be done, and people must be willing to support science over political agendas. More than anything, turning to renewable, clean energy sources will prevent CO2 emissions from causing further damage in the future.