Oysters, like many bivalves, are important for marine ecosystems. The organisms filter water through their feathered gills, removing impurities as they inhale and exhale. In fact, native and invasive bivalves might filter the entire volume of the San Francisco Bay every 3-4 days!

However, oysters around the world are threatened by ocean acidification. The acidity breaks down the calcium carbonate shells of the oysters, as we reported in a video several months ago.

Recently, researchers discovered other effects of acidification on oysters and what the breakdown of the oysters’ calcium carbonate shells could mean for the acidic balance. Science Today sat down with the Academy’s own oyster expert, Dr. Peter Roopnarine, curator and chair of Invertebrate Zoology and Geology, to get some perspective on these recent studies.

In the first study, published earlier this month, scientists reported that acidification has negative effects for oysters in the larval stage. The acidity in the water makes the larvae expend much more energy than in neutral waters to make their shells.

“As the oyster larvae struggle early on and expend that embryonic energy,” Roopnarine says, “they have difficulty cranking up their own feeding.”

According to the paper’s lead author, George Waldbusser, “It becomes a death race of sorts. Can the oyster build its shell quickly enough to allow its feeding mechanisms to develop before it runs out of energy from the egg? They must build their first shell quickly on a limited amount of energy—and along with the shell comes the organ to capture external food more effectively.”

Last month, headlines reported that “Oyster Shells are an Antacid to the Oceans,” based on a study of oyster reefs in Chesapeake Bay. Roopnarine explains how oyster reefs are built over time, “Oysters do best on hard ground. The first oysters in a soft bottom environment eventually become the hard substrate that future oysters build upon. As the reef grows, the presence of the shells promotes a healthy, low acidic environment.” Or as the study’s introduction states, “Active and dense populations of filter-feeding bivalves couple production of organic-rich waste with precipitation of calcium carbonate minerals, creating conditions favorable for alkalinity regeneration.”

On a micro-scale, like the Chesapeake Bay, Roopnarine agrees that this could work. Restoration of oyster reefs could contribute to the reduction of ocean acidification problems. On a macro-scale, over geological time and large ocean mass, however, it seems that these oyster reefs could do little to undo the large amounts of CO₂ humans have been pumping into air (that’s absorbed by the oceans) for over a hundred years.

I asked Roopnarine about the San Francisco Bay’s oyster population. We had native oysters before overharvesting, pollution and sedimentation from gold mining in the Sierras buried the oyster reefs, Roopnarine says. A few are still found around the bay, but their numbers are small.

The oysters farmed locally are Japanese oysters, which, until a few years ago, were only found in hatcheries. Wild populations are now establishing themselves in the bay, Roopnarine says, which could be due to warmer temperatures. He and colleagues wrote a study a few years ago that looks at the Japanese oyster population locally.

With the important work these marine organisms do, it’s important we learn more about them to restore oyster reefs.

A former Academy staff-member, Jill Bible, is doing just this near Bodega Bay. To learn more watch this great video by the UC Communications team.

Image: Oysters showing the effects of ocean acidification, OSU

Another climate and water story

Last week, we featured a series of stories on climate change and water issues and this one slipped by. A study in Nature last week reported how trees physically respond to drought. And the news is not good. Plants undergoing drought stress experience reduced pressure in the xylem (the vessel that transports water from the soil to the leaves).

Head over to NPR to read (or listen to) their piece on the study.

Melting ice sheets and sea level rise

A NASA/ESA study, published in Science this week provides the most thorough representation of the rate of melting ice sheets and corresponding sea level rise to date. Using extensive satellite data, scientists report that the ice sheets covering Greenland and Antarctica are losing more than three times as much ice each year as they were in the 1990s. About two-thirds of the loss occurs from Greenland, with the rest from Antarctica.

Combined, melting of these ice sheets contributed 0.44 inches to global sea levels since 1992. This accounts for one-fifth of all sea level rise over the 20-year survey period. The remainder is caused by the thermal expansion of the warming ocean, melting of mountain glaciers and small Arctic ice caps, and groundwater mining.

“Both ice sheets appear to be losing more ice now than 20 years ago, but the pace of ice loss from Greenland is extraordinary, with nearly a five-fold increase since the mid-1990s,” NASA’s Erik Ivins says.

Ocean acidification and fighting back

Ocean acidification is already having an effect on marine life, according to a study published this week in Nature Geoscience. Shells of live mollusks from the Southern Ocean are showing signs of “severe dissolution.” New Scientist has more information.

Washington State is taking action to curb ocean acidification and protect the state’s large shellfish industry. A report, released this week, outlines plans to target pollution that causes acidification (including carbon emissions and agriculture run-off) and has a $3.3 million backing. More information is available here.

Maybe more coastal states (and nations) will follow Washington’s lead, says the Ocean Conservancy.

A Sad Factoid

A final thought from the editors at grist.org, who note that “if you’re 27 or younger, you’ve never experienced a colder-than-average month.” A truly sobering fact gleaned from the NOAA “State of the Climate” report for October 2012.

Image: Ian Joughin