Laura Nielsen for Frontier Scientists
Will ocean acidification spell a watery grave for vital parts of marine ecosystems? Marine ecologist Jane Lubchenco, head of the National Oceanic and Atmospheric Administration, named ocean acidification global warming’s “equally evil twin.” *
Burning fossil fuels — coal, oil, natural gas — cutting down forests and other post-industrial revolution human activities have added more than 500 billion tons of carbon dioxide (CO2) to the atmosphere over the last 200 years. This anthropogenic (human-caused) increase in CO2 and other greenhouse gasses continues to influence dangerous climate change. The ocean acts as a carbon sink, meaning that it absorbs CO2 from the atmosphere. This causes ocean acidification: the ocean becomes more acid as it absorbs more and more CO2.
The pH scale measures acidity. Its lowest measurement, 0, represents strong acids. Its highest measurement, 14, represents strong bases. A netural measurement is 7, the pH of distilled water. Seawater near the ocean’s surface should have a pH of 8.2. In the last 200 years, heightened levels of CO2 have reduced surface seawater pH by 0.1, making the water 30% more acidic. With present trends, seawater will be 150% more acidic than in pre-industrial times by 2100. Heightened acidity increases concentrations of hydrogen ions in seawater. It also ties up calcium ions and thus creates a scarcity of calcium carbonate. Calcium carbonate is required by calcifying marine organisms to build stony skeletons and hard shells.
Coral polyps are tiny creatures that live and die in colonies. Their stony exoskeletons stack atop each other and, over time, construct coral reefs. But those exoskeletons are formed of calcium carbonate, which is less available when the sea is acidic. Ocean acidification is yet one more threat against coral colonies, which already face bleaching due to heightened water temperatures, competition from algae growths being fed by agricultural fertilizer runoff, infections, and disrupted ecosystems due to overfishing. When the coral reefs die, a vast network of marine organisms is left without a home or feeding ground. And experiments suggest that by 2050, the acidity level in surface-level seawater will be so high that coral reefs will begin to literally disintegrate.
Shellfish face similar risks. Clams, oysters, scallops, mussels, crabs, and lobsters all require hard shells built with calcium carbonate. While some species seem able to adapt to acidic waters, the heightened energy required to make hard shells takes resources away from other functions like growth or reproduction. Other species are unable to adapt, and grow weak, brittle shells. Less-noticed calcifyer organism like snails, sea urchins, one-celled calcifying plants called Coccolithophores, and tiny shelled sea snails known as Thecosomata Pteropods also require calcium carbonate based shells. Pteropods in particular feed myriad other species of fish (including salmon, mackerel, herring, cod), birds, and even whales. Declines in populations of shellfish and organisms at the bottom of the food chain directly disrupt food webs and threaten the livelihood and food security of humans around the globe.
Besides disrupted food chains, fish face physiological effects when the ocean becomes more acidic. An altered pH level can interfere with the ability of species to reproduce. Some sea urchin species’ sperm swim more slowly in acidified waters. Brittle sea star larvae disintegrate, while adult stars lose muscle mass or become unable to regenerate arms. Clownfish and damselfish larvae, which use their sense of smell to find shelter and avoid predators, have a reduced sense of smell in acidic water. Squid (another important prey species and commercial fishing species) experience a change in blood chemistry; lowered levels of oxygen in their blood interfere with their ability to swim efficiently. Fish eggs and larvae sometimes develop improperly when exposed to less-than-optimal ocean water chemistry.
The challenges which species face due to ocean acidification will mean that some species adapt and thrive, while others struggle and are pushed out by better-performing fellows. Algae and jellyfish, which thrive in acidic waters, will supplant other species’ niches, making for a less diverse ecosystem. Marine and costal food chains will be disrupted, disrupting in turn human commercial fisheries and fishing trades. The availability of iron and nitrogen nutrients will fluctuate, as some marine microbes find more success in altered conditions. Different amounts of sunlight will reach ocean depths, as populations of the microbes and tiny organisms which collonize the water change. And altered chemistry composition of seawater will likely reduce how much noise is muffled underwater, making low-frequency sound able to travel further and making the oceanic environment noiser. With our current knowledge, we are unable to foretell exactly how the complex ocean ecosystems will change, but it is very likely they will change for the worse. As with global warming, vastly decreasing the amounts of CO2 which humans are adding to the atmosphere is the optimal solution.
In 2011 the University of Fairbanks Alaska and NOAA’s Pacific Marine Environmental Laboratory collaborated to place 3 bouys which will allow scientists to track how seawater pH changes in arctic waters. “Coastal seas around Alaska are more susceptible to ocean acidification because of unique circulation patterns and colder temperatures. These factors increase the transport of carbon dioxide from the atmosphere into surface waters.” ** One bouy is placed near Seward, Alaska, while the second sits in the Bering Sea, and the third in the Chukchi Sea. With more complete data, researchers can continue to increase our understanding of ocean acidification and the future we face.
- *Jane Lubchenco, marine ecologist, head of the National Oceanic and Atmospheric Administration in “The Acid Sea” by Elizabeth Kolbert http://ngm.nationalgeographic.com/2011/04/ocean-acidification/kolbert-text/1
- **Jeremy Mathis, assistant professor of chemical oceanography at the University of Alaska Fairbanks in “UAF installs first ocean acidification buoy in Alaska waters” by Carin Stephens http://www.sfos.uaf.edu/news/story/?ni=385
- Northwest Association of Networked Ocean Observing Systems “Ocean Acidification is on the Rise” by NANOOS http://www.nanoos.org/data/products/noaa_ocean_acidification/summary.php
- Oceana “Effects of Ocean Acidification on Marine Species & Ecosystems” by Oceana oceana.org/en/our-work/climate-energy/ocean-acidification/learn-act/effects-of-ocean-acidification-on-marine-species-ecosystems
- National Oceanic and Atmospheric Administration : Pacific Marine Environmental Laboratory Carbon Program “OA Research” by NOAA : PMEL http://www.pmel.noaa.gov/co2/story/OA+Research
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