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Images: Sassy Scallops

For her Ph.D. research at WHOI, Meredith White used a plexiglass "look-box" to view the sandy bottom off Cape Cod shorelines to find scallops for her experiments. She bundled up to collect them in winter before rising water temperatures triggered gametogenesis, the development of the sperm and eggs that spawning scallops send into the water to create scallop larvae. (Daniel Ohnemus, Woods Hole Oceanographic Institution)

Back in the lab, MIT/WHOI Joint Program graduate student Meredith White is smiling because for the first time, she successfully coaxed the scallops she collected to spawn in beakers. She isolated the scallop larvae to chronicle how they developed in their crucial first hours and days of life, under various conditions and scenarios.

(Skylar Bayer)

To investigate how more acidic seawater conditions affected the development of scallop shells, Meredith White conducted classic "switch experiments" on scallop larvae. She grew them under four different sets of conditions: a subset  in only ambient seawater; a subset that spent their first 12 hours in ambient seawater and then were subjected to more acidic seawater with a pH of 7.4; another subset of larvae grew only in acidified water; and a final subset spent their first 12 hours in acidified seawater and then were switched to ambient water. 

(Meredith White)

Meredith White's results, published April 2013 in the journal PLOS ONE, showed scallop shell development for seven days, under three sets of conditions: ambient seawater (top); seawater with a high carbon dioxide level for three days, followed by ambient seawater for four days; and seawater with a high carbon dioxide level. Larvae shown represent the mean shell length for each treatment and age. The outline of each image corresponds to the CO2 treatment the larvae were experiencing at the time when the specimen was preserved in alcohol. Gray = ambient CO2, black = high CO2. Images are all to the same scale; scale bar = 100 µm.

(White, McCorkle, Mullineaux & Cohen, PLOS ONE)
Since the Industrial Revolution, increased burning of fossil fuels has sent more carbon dioxide into our atmosphere. Almost 30 percent of that carbon dioxide has been absorbed by the ocean, causing a fundamental change in the seawater chemistry. The carbon dioxide reacts with water molecules, creating more free hydrogen ions that drive down the pH of seawater and make it more acidic. Some of the hydrogen ions bind with existing carbonate ions in seawater to form bicarbonate. The net result is that the concentration of carbonate ions declines, so that corals have less of it to build their skeletons. Scientists predict that by the end of this century, the concentration of carbonate ions that corals need to grow will drop to less than half of preindustrial levels.
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