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Acidified water may also affect other aspects of an organism's physiology
In a previous experiment involving a sub-Arctic pteropod, Fabry grew the species at a lower carbonate ion saturation. Within 48 hours, the growing edge of the shell began to dissolve. “The shells start to get pitted, the upper layer peels off, and that exposes more calcium carbonate rods and crystals to dissolution, and they just dissolve,” she said.
The team is conducting similar experiments here over two field seasons, though weather for this second year stymied collection efforts for the first couple of weeks. The scientists are after two types of pteropods: one with a shell in its adult stage (euthecosomatous pteropods), and a second, carnivorous species (gymnosomatous pteropods) that feeds exclusively on the first.
Seibel, a co-principal investigator on the project, is interested in discovering how ocean acidification will affect other aspects of pteropod physiology, such as oxygen consumption or ammonia excretion.
“CO2 causes acidification in body fluids the same way it does in seawater, although not necessarily to the same extent,” said Seibel, with the University of Rhode Island. “Acidification of the body fluids can lead to changes in metabolism that could lead to reductions in growth and reproduction.
“In other oceans, we’ve seen detrimental effects of CO2 on squid metabolism,” he added.
Very preliminary results show little effect on the pteropod physiology to high levels of CO2 — 1,000 parts per million, about triple the concentration in the oceans today. However, Seibel emphasized that the experiments are short duration. The studies on squid, whose blood has a protein that binds to oxygen to transport it around the body, showed pronounced responses to acidified water.
“That protein is very sensitive to pH, so we are able to see changes in oxygen consumption with these levels of CO2 in squids,” he said.
The team’s method of specimen collection is pretty low-tech. Members put on chest waders and walk into the water from shore. They then use a long broom handle with a beaker at one end to gather the pteropods. “We just dip them up, because they’re very, very fragile,” Fabry said.
The shelled pteropods don’t live long in captivity because they feed by means of a mucous web that is suspended above their bodies, sort of like a free-floating, omnivorous spider surfing its web through the water as it feeds.
In the lab, the scientists measure how much the pteropods calcify under varying levels of ocean acidification based on predictions from the Intergovernmental Panel on Climate Change. For Seibel’s purposes, the researchers track rates of oxygen consumption and ammonia excretion, as well as measure the acidification in animal tissues.
Fabry said it is too early to say how well the organisms may be able to adapt as worldwide surface ocean pH drops. She noted that oceans could absorb CO2 and eventually neutralize it but that process takes thousands of years. Ocean acidification, beginning in the 1800s, is occurring over the span of a few centuries.
“The rate of release of CO2 to the atmosphere is critical. We could put more CO2 in the ocean, if we did it slowly,” she explained. “The biggest unknown is how fast humans will put CO2 in the atmosphere.”
NSF-funded research in this story: Victoria Fabry, California State University San Marcos; and Brad Seibel, University of Rhode Island.