In a bit of unexpected climate related good news—not for us, of course—some shell-building ocean dwellers like blue crabs, shrimp, and lobsters may actually benefit from increased ocean acidification. This surprising finding seems to be good news for lobster lovers, but researchers note that the ongoing acidification still appears to spell trouble for many marine creatures.
Scientists now think that acidifying oceans may allow these select crustaceans to build stronger shells and exoskeletons, instead of making them more brittle. Carbon dioxide (CO2)—the notorious byproduct of fossil fuel burning—dissolves in the ocean. That makes the ocean more acidic. It also reduces the number of so-called carbonate ions in seawater, and these ions are among the primary materials that sea creatures use to build their calcium carbonate shells and skeletons [LiveScience]. Justin Ries, a coauthor on the new study, speculates that these bottom dwellers are somehow better able to manipulate CO2 ions to build their shells, even though fewer CO2 ions are available to them in an acidic environment. However, exactly how they accomplish this is unknown.
Previously, scientists thought that all marine invertebrates would disappear as the oceans became more acidic. However, many of these creatures were alive during the Cretaceous period about 100 million years ago when CO2 levels were 10 times pre-Industrial levels. To see if they would all wither away in acidic oceans, Ries and colleagues exposed 18 species of marine organisms to seawater with four levels of acidity. The first environment matched today’s atmospheric CO2 levels, and two others were set at double and triple the pre-Industrial CO2 levels, mimicking conditions predicted to occur over the next century. The fourth CO2 level was 10 times pre-Industrial levels [ScienceNOW Daily News]. The results are a mixed bag for the organisms tested.
Blue crabs, shrimp, and lobsters, became juiced on the increased CO2, the researchers report in the journal Geology. However the news is not all good because American oysters, scallops, temperate corals, and tube worms developed thinner shells at the highest CO2 levels. The exoskeletons of clams and pencil urchins practically dissolved at the highest CO2 levels.
For clams and pencil urchins, the findings are troubling, since their shells and spikes are more than just pretty accessories—they serve as armor against their predators. In fact, the researchers found that creatures whose shells grew the most, such as crabs, tend to prey on those whose shells weakened the most, such as clams [NatGeo News Watch]. However for the super-sized animals, getting bigger may come with a cost, since extra energy spent building thicker shells “might divert from other important processes such as reproduction or tissue building,” [USA Today] said study coauthor Anne Cohen.
Says author Ries: “The take-home message is that the responses to ocean acidification are going to be a lot more nuanced and complex than we thought” [ScienceNOW Daily News].
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Image: Justin Ries / University of North Carolina, Chapel Hill