Global warming is expected to cause such alarming climate disruptions that talk of hurricanes and heat waves can overshadow another drastic process at work: Burning fossil fuels and otherwise producing excess carbon dioxide makes oceans and other bodies of water more acidic, as the water absorbs the gas. This acidification can change a fish’s physiology in ways that were previously unpredicted and could affect the fish’s survival, according to a study in Science.
Scientists raised groups of white sea bass in water of varying concentrations of carbon dioxide. They found that the fish in the most highly acidified water had the largest rock-shaped ear bones, known in biology parlance at otoliths. That contradicts what the researchers had hypothesized: The ear structure in fish, known as an otolith, is made up of minerals. Scientists knew that increasing carbon dioxide in the oceans — absorbed from the atmosphere — is making the sea more acidic, which can dissolve and weaken shells. They wondered if it also would reduce the size of the otoliths [Los Angeles Times]. Instead, the ear bones of fish growing in the tank with six times as much carbon dioxide than normal were 15 to 17 percent larger than normal. An water with a CO2 concentration about 3.5 times higher than current levels yielded fish with otoliths that were 7 to 9 percent larger than those raised in water with today’s carbon dioxide levels. That’s the CO2 level predicted by the year 2100.
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While concerns over ocean acidification are not new, a recent study provides more concrete evidence than ever before that the process has already begun. Australian scientists found that shells of the microscopic, amoeba-like organisms called foraminifera, which exist by the billions in oceans around the world, have become significantly thinner since the Industrial Revolution.
The study, published in Nature Geoscience, is the first to look specifically at acidification and pin it to greenhouse-gas pollution, which is driven especially by the invisible product of burning oil, gas and coal. “It is the invasion of anthropogenic (man-made) CO2 that is causing this particular source of acidification,” said co-author William Howard [AFP].
The research team compared newer shells of Globigerina bulloides, a species of foraminifera, with shells of the same species that had sunk hundreds of years earlier; the modern shells were found to be 30 to 35 percent lighter than older specimens of about the same size. The older shells predate the industrial age, when CO2 levels started rising and the acidity of the ocean, caused by the absorption of the gas, began to increase…. As ocean acidity increases, the saturation levels of carbonate minerals in the water decreases, making it more difficult for organisms to precipitate out the carbonate for their shells [The New York Times].
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Ocean acidification, the second part of the one-two punch packed by global warming, has been shown to disorient young clown fish and prevent them from finding their way to their natural habitats. A new study found that dropping the pH of seawater interfered with the fish’s ability to sniff out environmental cues. Most research on the environmental impacts of acidification has focused on the vulnerability of shellfish, corals and crustaceans, whose shells are weakened and dissolved by acidic waters. But the latest findings show that fish may also be directly and profoundly affected [Wired News].
A little like the animated movie-star clown fish, Nemo’s real-life counterparts go out to sea upon hatching and some 12 days later must find their way back to a reef to settle down in an anemone home [Science News]. Researchers believe that the fish find their way by following odors in the water. In the new study, published in the Proceedings of the National Academy of Sciences [subscription required], researchers raised clown fish in tanks filled with water of varying pH, and then tested their ability to follow scents.
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Chalk up another potential victim of global warming. A new study warns that the jumbo squid (also known as the Humboldt squid) may not fare well in the coming decades, as the oceans get warmer and absorb carbon dioxide from the atmosphere, which makes the water more acidic. Jumbo squid blood carries very little oxygen – with each cycle through its body, the oxygen can be used up entirely. This means they must “recharge” constantly, and makes the animals very dependent on what oxygen is available in the water around them. Yet, the warmer water is, the smaller the amount of oxygen it can hold [New Scientist].
What’s more, the squid’s blood cells can carry less oxygen in acidic water. Their blood-oxygen delivery system is highly sensitive to pH, so “the organisms are thought to live chronically ‘on the edge of oxygen limitation,’” the authors wrote. During the day, the squid descend to lower depths in the ocean to rest, slowing down their metabolism to deal with the lower oxygen levels there. At night, they return to well-oxygenated waters nearer the surface to feed [LiveScience]. However, if surface waters are both warmer and more acidic, the squid trying to feed at the surface will get much less oxygen, which will slow down their metabolisms. And lethargic squid are easy targets for predators like sperm whales, researchers say.
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Ocean acidification is happening at 10 to 20 times the rate predicted by existing climate models, according to an eight-year study. The rapid acidification of the oceans is linked to global warming and may be a sign that the oceans, the largest absorber of atmospheric carbon dioxide, may not be as hardy as presumed. The changes threaten disaster for marine life with shells that are easily corroded by acid. Marine biologist Nancy Knowlton said, “This is typical of so many climate studies—almost without exception things are turning out to be worse than we originally thought.” [National Geographic News].
The study was done around Takoosh Island off the coast of Washington state and represents the first detailed dataset on variations of coastal pH at a temperate latitude, where the world’s most productive fisheries are found [Times of India]. The researchers took over 24,000 measurements of ocean pH over an 8-year period. During that time, the pH of the seawater was predicted to decrease by only 0.015 points. Instead, the data showed that seawater pH dropped by 0.36 to about 8.1. “The increase in acidity we saw during our study was about the same magnitude as we expect over the course of the next century,” said study co-author Timothy Wootton [National Geographic News].
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Using boat, tags, nets, and submarines, marine biologists from 82 nations have been canvassing the oceans for the first Census of Marine Life, an ambitious effort to get a rough tally of all the creatures in the world’s oceans. The 10-year project is expected to conclude in 2010, and researchers say the broad survey will help them observe changes to marine ecosystems. Says co-senior scientist Ron O’Dor: “We are moving into this period of global warming, which is resulting in the acidification of the oceans, melting of the polar ice cap. We can use the first census as a benchmark to see what happens in the oceans over the next decade or more” [BBC News].
Although the project still has two years to go, researchers have already made a host of startling discoveries, many of which will be discussed this week at the World Conference on Marine Biodiversity in Valencia, Spain. In one study, researchers conducted a genetic analysis of deep sea octopuses from around the world, and determined that most descended from a common ancestor species that still lives near Antarctica. Researchers believe that octopuses started migrating to new ocean basins more than 30 million years ago when, as Antarctica cooled and a large icesheet grew, nature created a “thermohaline expressway,” a northbound flow of tasty frigid water with high salt and oxygen content. Isolated in new habitat conditions, many different species evolved; some octopuses, for example, losing their defensive ink sacs — pointless at perpetually dark depths [LiveScience].
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Coral reefs can resemble underwater monuments, with strong towers and meandering walls that stand firm against the tides. But a new study says that if global warming causes ocean water to become more acidic those elaborate structures may crumble because the cement-like binding agent that holds the reefs together won’t be able to form in those inhospitable waters.
Most of the world’s coral reefs aren’t yet showing signs of this degradation, as ocean pH is slow to change and reefs form slowly. But researchers got a chance to peer into the possible future in an area of the eastern Pacific off Central America… where the water is more acidic than elsewhere, thanks to the upwelling of carbon-dioxide-rich waters. Coral reefs in this region are poorly developed and tend to erode rapidly [The New York Times].
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Of all the potential effects of global warming on the natural world, one of the most alarming (and how hard it is to choose!) is the expected acidification of the planet’s oceans. Because much of the carbon dioxide that humans pump into the atmosphere ends up in the oceans, and because dissolved carbon dioxide makes water more acidic, researchers expect the pH balance of the oceans to shift further towards the acidic side of the scale before the end of the century.
Environmental scientists had a pretty good idea of what that would mean for the marine ecosystem, but a new study published in the journal Nature [subscription required] gives researchers a small-scale glimpse at that future. An international team of marine biologists studied natural carbon dioxide vents on the sea floor, and examined the consequences on biodiversity and individual species.
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