for National Geographic News
So says a new study showing that more acidic oceans, a consequence of rising atmospheric carbon dioxide (CO2) levels, can produce jumbo-size shelled marine species, including lobsters, crabs, and shrimp. It's unknown whether the animals' body mass also gets beefier along with their shells. (Learn about greenhouse gases.)
But it's not good news for all sea creatures. In the experiment, other species—including oysters, scallops, and clams—suffered in more acidic waters because they had more trouble building their shells.
That's because rising CO2 levels boost the amount of carbon in the oceans, but reduce levels of the carbonate ion that marine organisms need to make their protective shells.
Study leader Justin Ries, of the University of North Carolina at Chapel Hill, and colleagues grew 18 species of shelled marine animals in conditions that mimicked the elevated CO2 levels predicted in Earth's atmosphere over the next two centuries.
The lobsters and other animals that thrived under higher CO2 levels during the experiment are better able to convert the inorganic carbon in seawater into a form they can use to produce shells.
Acid Tipping Point
The team also found that some species, such as calcifying algae, benefited from increased CO2 up to a point—and then quickly began to experience problems building their shells.
This may illustrate a specific CO2 "tipping point," which scientists could identify and monitor in future studies, according to the report published in December's Geology.
But even animals that grew larger in more acidic waters may ultimately suffer if an ocean food chain evolved over hundreds of millions of years is rapidly reorganized.
For instance clams—a main prey of crabs and lobsters—have "completely different" responses to rising CO2, Ries said.
"It's a scenario where the predator is getting stronger and the prey is getting weaker. The [clams] may not be able to sustain their populations and ultimately the predators will also be adversely impacted when the prey populations crash."
Ecological Engineers Threatened
The scenario also poses problems for "ecological engineers" such as coral, which at first had no response to the acidic water but then began to have trouble forming their shells, Ries said.
"If corals decline, like the experiment predicts, then all the organisms that need a coral reef to survive, like crabs and lobsters, are going to suffer, even though they are predicted to do well [in more acid conditions]," he said.
Likewise, the winners in acidic oceans may also see setbacks, he added.
For instance, if species are pouring more of their hard-earned energy into shell growth, other biological functions like reproduction may decline.
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