Some crabs, shrimps and lobsters build thicker shells despite oceans growing more acidic due to greenhouse gases, report marine biologists Tuesday.
Increasing carbon dioxide levels in the atmosphere have increased the ocean’s acidity, widely seen as a threat to corals and crustaceans need to build shells of calcium suspended in seawater. But in the Geology journal report, a team led by Justin Ries of the University of North Carolina reported that 7 of 19 shelled species tested under higher-acid conditions grew thicker shells in response.
“We were surprised that some organisms didn’t behave in the way we expected under elevated CO2,” said study co-author Anne Cohen of the Woods Hole Oceanographic Institution, in a statement. Despite global warming and rising carbon dioxide concentrations in the oceans, she adds, “we can’t assume that elevated (carbon dioxide) causes a proportionate decline in calcification of all calcifying organisms.”
However, some economically valuable species lost their shells right away at higher acid levels, notably oysters.
And the effects may the ecology of the oceans. Crabs improved shell-building while prey clam shells grew thinner at higher acid concentrations. “This may initially suggest that crabs could benefit from this shift in predator-pray dynamics. But without shells, clams may not be able to sustain their populations, and this could ultimately impact crabs in a negative way, as well,” Ries said.
And though crabs and lobsters may appear to benefit, extra energy spent building thicker shells “might divert from other important processes such as reproduction or tissue building,” Cohen says. Nobody likes a thick-shelled, puny, lobster-tail at the dinner table.
By Dan Vergano
Photo: The larger of these two pencil urchins was exposed to currrent CO2 levels; the smaller was exposed to the highest CO2 levels in the study.
Dan Vergano, USA TODAY, 1 December 2009. Article.