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Increasingly acidic oceans damaging to marine life

Increasingly acidic oceans harm marine life

Increasingly acidic oceans harm marine life
July 5, 2006

More bad news for the world’s sea creatures

Carbon dioxide emissions are altering ocean chemistry and putting sea life at risk according to a new report released today.

The report, “Impacts of Ocean Acidification on Coral Reefs and Other Marine Calcifiers,” summarizes known effects of increased atmospheric carbon dioxide on marine organisms that produce calcium carbonate skeletal structures, such as corals.

Oceans worldwide absorbed approximately 118 billion metric tons of carbon between 1800 and 1994 according to the report, resulting in increased ocean acidity, which reduces the availability of carbonate ions needed for the production of calcium carbonate structures.

“It is clear that seawater chemistry will change in coming decades and centuries in ways that will dramatically alter marine life,” said Joan Kleypas, the report’s lead author and a scientist at the National Center for Atmospheric Research (NCAR) in Boulder. “But we are only beginning to understand the complex interactions between large-scale chemistry changes and marine ecology. It is vital to develop research strategies to better understand the long-term vulnerabilities of sensitive marine organisms to these changes.”

“This is leading to the most dramatic changes in marine chemistry in at least the past 650,000 years,” says Richard Feely, one of the authors and an oceanographer at NOAA’s Pacific Marine Environmental Laboratory (PMEL) in Seattle. Atmospheric carbon dioxide levels are higher than at any point in the past 650,000 years.

Oceans becoming more acidic

Great Barrier Reef in Australia
Ocean acidification is of great concern due to its potential impact on marine life. Coral and other marine organisms use free carbonate ions in sea water to build calcium carbonate shells and exoskeletons, but as atmospheric carbon dioxide levels rise and more carbon dioxide is absorbed by the world’s oceans, sea waters become increasingly acidic by stripping out carbonate ions. Lower carbonate ion concentrations make it more difficult for organisms to form shells, leaving them vulnerable to predators and environmental conditions.

Research released earlier this year showed that the Pacific Ocean is getting warmer and more acidic, while the amount of oxygen is decreasing, due to increased absorption of atmospheric carbon dioxide. The pH of saltwater in the Pacific has dropped 0.025 units since the early 1990s and scientists warn that oceans could become even more acidic by the end of the century given current atmospheric carbon dioxide levels. Since there is a lag time in the absorption of carbon dioxide by oceans, the impact of past carbon emissions are not yet fully apparent.

Carbon dioxide is a byproduct of fossil fuels combustion. Scientists estimate that the oceans have soaked up about half–118 million tons of atmospheric carbon dioxide–of all fossil fuel emissions over the past 200 years. Had oceans not absorbed this carbon, current atmospheric carbon dioxide would be much higher than the current 381 parts-per-million (ppm)–probably closer to 500-600 ppm say climatologists.

This absorption has made the world’s oceans significantly more acidic since the beginning of the industrial revolution. According to Mark Jacobson, an assistant professor of civil and environmental engineering at Stanford University, between 1751 and 2004 surface ocean pH dropped from approximately 8.25 to 8.14. James Orr of the Climate and Environmental Sciences Laboratory estimates that ocean pH levels could fall another 0.3 – 0.4 units by 2100.

Threat to ocean biodiversity

The pteropod or sea butterfly is one marine organism that could suffer in more acidic seas. A recent experiment by Victoria Fabry at California State University San Marcos found that the shells of pteropods, when subjected to conditions as projected by the model for the year 2100, rapidly dissolved. Photo courtesy of USGS.

“Impacts of Ocean Acidification on Coral Reefs and Other Marine Calcifiers” outlines future research to understand the consequences of climate change for marine life. The report says that “while scientists cannot yet fully predict how much marine calcification rates will change in the future, the report warns that the more critical question is: ‘What does this mean in terms of organism fitness and the future of marine ecosystems?'”

In the past, changes in ocean acidity have caused mass extinction events. According to a study published in the September issue of Geology, dramatically warmer and more acidic oceans may have contributed to the worst mass extinction on record, the Permian extinction. During the extinction event, which occurred some 250 million years ago, about 95% of ocean’s life forms became extinct. The same fate could befall modern day marine life.

Experimental studies conducted by Chris Langdon, one of the report’s authors based at the University of Miami, show that “coral calcification consistently decreases as the oceans become more acidic,” resulting in slower growth and less-dense skeletal structures of marine organisms. Reef ecosystems are expected to suffer especially because “corals may be unable to build reefs as fast as erosion wears away the reefs.”

“This threat is hitting coral reefs at the same time that they are being hit by warming-induced mass bleaching events,” Langdon said. “Mass bleaching occurs when unusually warm temperatures cause the coral to expel the colorful microscopic algae that provide the coral polyps with food.”

Late last year a team of scientists writing in Nature warned that by 2100, the amount of carbonate available for marine organisms could drop by 60%. In surface ocean waters, where acidification starts before spreading to the deep sea, there may be too little carbonate for organisms to form shells as soon as 2050.

The loss of these small organisms would have a disastrous impact on predators — including salmon, mackerel, herring, cod — that rely on them as a food source and could spell trouble for other species.

“Decreased calcification in marine algae and animals is likely to impact marine food webs and has the potential to substantially alter the biodiversity and productivity of the ocean,” said Victoria Fabry, an oceanographer at California State University, San Marcos, and another of the report’s authors.

Marine calcifiers are key to ecosystems beyond coral reefs and increasing ocean acidity threatens these reservoirs of biodiversity as well. In April, a study published in Frontiers in Ecology and the Environment warned that coldwater reefs off the coast of Alaska and in the North Atlantic could be particularly affected.

Related articles

Coral reefs decimated by 2050, Great Barrier Reef’s coral 95% dead
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This article used quotes and information from a release from the National Center for Atmospheric Research. It also extensively used information from past news articles.

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