A Look Into Future Oceans for Shellfish Reasons

Carbon Dioxide, Absorbed by the Seas, Changes the Chemistry of Water and the Growth of Marine Life
By ROBERT LEE HOTZ

In the living laboratory of a submerged volcano, marine biologist Verena Tunnicliffe glimpsed sea creatures trying to survive in acidic oceans.
Carbon dioxide that bubbles up in the sulfur chimneys of the undersea Eifuku volcano near the Pacific's Mariana Islands has turned the water into an acidic broth, with striking effects on sea life. Scientists say the corrosive conditions there offer clues to how rising levels of man-made CO2 in the air could unbalance oceans world-wide.
To her surprise, Dr. Tunnicliffe found that mussel shells she collected at Eifuku were so thin that she and her colleagues could see right through them. The water chemistry made it impossible for the mussels to extract enough calcium carbonate to form a proper covering. Compared with shells of the same species collected in more normal waters, "they were half the thickness and half the weight," she said.
Known as the rain forests of the sea, coral reefs teem with life. Now, scientists say these important habitats are under threat. WSJ's Science Journal columnist Robert Lee Hotz reports.
Recommended Reading
Exploration of life on the undersea volcano Eifuku was reported in "Survival of mussels in extremely acidic waters on a submarine volcano," published in Nature Geoscience.
A team of Australian researchers documented the effects of ocean acidity on plankton shells in "Reduced calcification in modern Southern Ocean planktonic foraminifera."
University of Chicago researchers measured increasing coastal ocean acidity in the Pacific Northwest in The Proceedings of The National Academy of Sciences.
In January, researchers at the Australian Institute of Marine Science measured the impact of ocean acidity on the Great Barrier Reef in "Declining Coral Calcification on the Great Barrier Reef," published in Science.
An international research team calculated the effects on coral reefs of rising CO2 emissions in "Coral reefs may start dissolving when atmospheric CO2 doubles," in Geophysical Research Letters.
An international research effort assessed the impact of CO2 on oceans in "Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms," in Nature.
Researchers systematically calculated the amount of man-made CO2 absorbed by oceans since 1800 in "The Oceanic Sink for Anthropogenic CO2," published in Science.
To live in these inhospitable conditions, the mollusks cannibalized their own shells, leaching from them the carbonate needed to maintain their internal muscle chemistry. "They are dissolving whatever shell they do have," says Dr. Tunnicliffe at the University of Victoria in British Columbia. They manage to survive despite their weakened shells, the scientists speculated, because the water's harsh chemistry is too much for the hard-shell crabs that prey on these mussels elsewhere.
When the mussels die, their wafer-thin shells disintegrate even faster than their soft tissues can decay.
To be sure, the sea chemistry of Eifuku is unusual by any measure. Located on the volcanic rim of the Mariana Trench near the island of Guam, the mollusks live in water pressure 44 times that at the surface, at one of only two spots in the world where CO2 rises from the seabed as a liquid. Dr. Tunnicliffe and her colleagues explored the beds of exotic vent mussels during a 2006 expedition via the sensors of a sturdy deep-sea robotic explorer called Jason-II. They reported their findings last week in the journal Nature Geoscience.
Conditions on the volcanic slopes of Eifuku have been this acidic for millennia, giving these creatures more than enough time to acclimate. But many oceanographers worry that increased CO2 -- likely created by burning fossil fuel -- is changing sea chemistry world-wide more quickly than most marine life can adapt. A host of experiments are underway to assess just how the increased CO2 levels are changing ocean life.
From the rocky inlets of Tatoosh Island in the Pacific Northwest to Australia's Great Barrier Reef, seawater is turning acidic. Mounting evidence suggests plankton, sea urchins, squid, coral and other marine life already find it harder to grow, reproduce and survive. If acidification intensifies, it could ultimately threaten the marine food chain, including commercial fisheries.
Pfister, University of Chicago
Dead mussels along Tatoosh Island in the Pacific Northwest, where seawater acidity has risen faster than expected.

All told, the oceans have absorbed 118 billion tons of carbon in the 200 years since the beginning of the industrial revolution, an international research team led by oceanographer Christopher Sabine at the Pacific Marine Environmental Laboratory in Seattle has calculated. Every second of the day, the oceans absorb an additional 300 tons of CO2 emissions.
In seawater, CO2 forms carbonic acid, steadily lowering the ocean's pH value on a scale used to gauge a liquid's acidity or alkalinity. The number gets lower as a liquid gets more acidic. Fresh milk has a pH of about 6.7; lemon juice has a pH of 2.4 or so. The concern is that quickly falling pH levels could overwhelm a species' chemical stability.
"If CO2 levels in the atmosphere rise, then the oceans become more acidic," says marine ecologist Jon Havenhand of Sweden's University of Gothenburg. "The chemistry is unavoidable."
For at least 600,000 years, the oceans maintained a steady pH of about 8.2, according to levels measured in ancient ice cores that preserve an annual chemical record of times past in the same way that tree rings do. Since 1800, however, the pH of seawater has dropped to 8.1. "The number is small but the change is substantial," says marine biologist Donald Potts at the University of California, Santa Cruz. By the end of this century, the pH of seawater is expected to drop to 7.8 or so.
The change in sea chemistry affects how easily marine creatures can form the calcium carbonate materials for shells and skeletons. "As it gets more acid, they lay down skeletons more slowly and they make a softer skeleton, with less strength," he says.
Last month, President Barack Obama signed a new wilderness law that calls for federal agencies to assess the impact of rising ocean acidity. The measure also authorizes an ocean acidification research program led by the National Oceanic and Atmospheric Administration. Last week, the U.S. Environmental Protection Agency for the first time began weighing the possibility of revising pH standards under the federal Clean Water Act to prevent ocean acidification.
ROV RoPOS, NOAA Exploration Program
High acidity surrounding the undersea Eifuku volcano offers a model of how carbon dioxide might affect marine life elsewhere.
Jacqueline Savitz, a senior scientist at the conservation group Oceana, says regulators should move quickly. Already, coral growth across the Great Barrier Reef has slowed, researchers at the Australian Institute of Marine Science reported in Science earlier this year. The rate at which the corals at 69 reefs across the formation absorb calcium from seawater has declined precipitously in the last 20 years.
In a computer study made public last month, researchers at the Carnegie Institution for Science and the Hebrew University of Jerusalem analyzed conditions at 9,733 reefs around the world and then calculated the impact of CO2 emissions. The scientists found that rising CO2 levels in the atmosphere threaten the reefs' ability to replenish themselves. "If you double the CO2, it's twice as hard for them to build their skeletons," says Carnegie oceanographer Ken Caldeira.
The changing carbon chemistry already is affecting some marine organisms, several new scientific studies show.
Off the coast of Washington state, for example, mussels and barnacles were edged out of traditional beds by more acid-tolerant algae as pH levels plummeted over the past eight years, University of Chicago researchers found. "The acidity was dropping to levels that haven't been expected at all," says Chicago ecologist Timothy Wooten. "We are scrambling to understand what is going on there."
At Gothenburg University, researchers found that more acidic seawater cut fertilization rates among sea urchins by 25%. Some species of shellfish, though, were indifferent to lower pH changes, their tests showed. One mollusk species thrived. So far, there are no other known benefits from the changes.
"It's unpredictable," Dr. Havenhand says.
Australian researchers recently analyzed shells of modern plankton, called foraminifera, which teem by the billions in the Southern Ocean surrounding Antarctica. The scientists compared shells today with those from cores of sea-floor sediments dating back 50,000 years. The modern plankton made shells 30% to 35% lighter than their ancestors, suggesting today's plankton can't get enough calcium carbonate.
Indeed, the plankton now can't build shells as large as those of even a century ago. The change, scientists say, is not part of any natural ocean cycle but due to CO2 from burning fossil fuels over the last 100 years.
"We can actually detect the isotopic signature of CO2 from fossil fuels in the ocean and in the shells of these organisms," says marine geologist William Howard at the Antarctic Climate and Ecosystems Cooperative Research Centre in Hobart, Tasmania, who led the study. "For good or ill, this is where the CO2 is coming from."
Robert Lee Hotz also shares recommended reading on this topic and responds to reader comments at WSJ.com/Currents. Email him at sciencejournal@wsj.com.