Ocean acidification is the process by which the ocean absorbs carbon dioxide (CO2) from the atmosphere. The oceans have regulated Earth´s climate by absorbing CO2 from the atmosphere for centuries; however, in the present, the chemistry of the oceans is being altered significantly, as the ocean is absorbing more CO2 than it has in the past. The ocean is 30 percent more acidic today than it was before the industrial revolution and is expected to increase its acidity by 100-150 percent by the end of the 21st century. Ocean acidification is having a significant impact on many biological and chemical processes occurring in the marine ecosystem and is expected to have a profound impact in the following decades.
What is ocean acidification?
The interaction between CO2 and ocean water causes the formation of carbonic acid, reducing the pH of water. An increase in ocean acidity decreases carbonate ions, preventing the buildup of skeletons and shells in a wide variety of marine organisms. Initially, the absorption of CO2 from the atmosphere by the ocean was seen as a beneficial process; however, careful observations have shown that the CO2 absorbed by the ocean is changing the chemistry of sea water in a process known as ocean acidification. Ocean acidification not only affects marine life but entire ecosystems, such as coral reefs.
Effects on marine life
Many marine life forms depend on calcium (Ca) and carbonate (CO3) to form their skeletal and shell structures. When the pH decreases, due to high concentrations of CO2 in the ocean water, carbonic acid is build up in an organism´s body fluids, preventing the secretion of calcium carbonate (CaCO3), which is the material that helps them build up their shell structures. Lowered pH may affect not only marine animals with a calcium carbonate structure, but other higher forms and fish, as well. The acidosis in the tissues and fluids of these animals may lead to metabolic dysfunction, lowered resistance and behavioral changes, affecting reproduction and physical activity.
Marine animals interact in dynamic food webs, and the change in survivability of marine animals with calcium carbonate structures may disrupt the survivability of other species which feed on them. Ocean acidification threatens some species of plankton. Plankton is at the base of marine food chains for larger organisms. The acidity of the ocean threatens organisms that depend on small calcium carbonate shelled organisms, such as marine snails (pteropods), for their survival. Bigger animals, such as whales, base their diet on these tiny animals. Pteropods are predicted to become extinct by the end of the 21st century due to high acidity levels, affecting the marine ecosystem.
Effects on marine ecosystems
The increasing acidity of ocean water decreases the ability of coral reefs to construct their carbonate skeleton, causing a slow growing rate of the reef´s structure and higher vulnerability to erosion. It is expected that the gradual reduction of the calcification rate may surpass the erosion rate, preventing a coral reef build-up by calcification. Coral reefs are very sensitive to changing temperatures, and higher concentrations of CO2 in the atmosphere may cause a phenomenon known as bleaching, in which the corals release their algal symbionts, leaving the coral´s tissues transparent. Although corals can recover from bleaching, subsequent events are likely to cause tremendous damage to the ecosystem.
Effects on economy
Although coral reef ecosystems occupy less than 0.1 percent of the world´s ocean area, they are the habitat of approximately 25 percent of all marine species. It is estimated that nearly 500 million people base their diet on the marine life that thrives on the coral reef ecosystem. The coral reef ecosystem delivers services to the tourist industry and fisheries. It is estimated that the annual global economy provided by coral reefs encompasses more than $350 million; however, coral reefs are fragile ecosystems which are threatened by high water temperatures and ocean acidification caused by CO2 concentrations in the atmosphere.
The release of CO2 into the atmosphere from human activities has increased from 280-385 parts per million (ppm) since the industrial revolution. Before the industrial revolution, CO2 concentrations remained between 180 and 300 ppm. The concentrations of CO2 in the atmosphere are higher, in the present, than it has been during the last 650,000 years, and this trend is expected to continue during the following decades. According to the Marine Conservation Institute, the only long-term solution to ocean acidification is a gradual reduction of CO2 concentrations in the atmosphere.
