Archive for December 2009
Ocean acidification modifies some marine life
A Sally Lightfoot Crab (Grapsus grapsus) sits atop a rock, Galapagos Island, Ecuador. A recent study found hard shelled crabs and lobsters grew thicker shells when exposed to more acidic ocean water.
Courtesy, kookr @ flickr
As the amount of carbon dioxide in Earth’s atmosphere increases, the ocean too sees higher dissolved carbon dioxide levels. This is because the ocean is a natural carbon dioxide filter, or sponge, as earlier reported in Carbon dioxide absorbed by ocean diminishes.
Ocean water pH falls as more carbon dioxide is absorbed, making the ocean more acidic. For the most part, acidification of the ocean concerns marine researchers.
Organisms with shells were previously thought to be the most seriously effected by acidification. Because, As Science daily reports, “carbon dioxide is known to trigger a process that reduces the abundance of carbonate ions in seawater — one of the primary materials that marine organisms use to build their calcium carbonate shells and skeletons.”
This prompted a recent study were organisms were exposed to varying levels of dissolved carbon dioxide. The results surprised researchers. According to a University of Chapel Hill study published in Dec, by the scientific journal, Geology, some crab, shrimp and lobster living in more acidic sea water actually grow thicker shells.
“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. “We can’t assume that elevated (carbon dioxide) causes a proportionate decline in calcification of all calcifying organisms”
Science daily reports Justin B. Ries, an author of the study, thinks the shelled animals were “somehow able to manipulate CO2…to build their skeletons.”
While it is clear that some organisms are not negatively impacted by high dissolved carbon dioxide levels, researchers explain this may still be bad news for sensitive ocean ecosystems. Seven of the 18 shelled species were able to build more calcium carbonate shell, but National Geographic explains, “Ten types of organisms (including oysters, scallops, temperate corals and tube worms) had reduced calcification under elevated CO2, with several (hard and soft clams, conchs, periwinkles, whelks and tropical urchins) seeing their shells dissolve.”
This could also led to shifts in the predator-prey relationship. “There is no magic formula to predict how different species will respond, but one thing you can be sure of is that ecosystems as a whole will change because of these varied individual responses,” Ries said in a statement.
So, while it may be both interesting and surprising that a few organisms are benefiting from ocean acidification and global warming in general; it’s important to view ocean ecosystems on a larger scale. Larger, stronger shells might provide a temporary advantage, but food chains come full circle. Crabs for instance, feed on clams, which saw their shells dissolve in the acidic sea water. No matter how thick their shells grow crabs will always need something to eat. Perhaps thicker shells aren’t so advantageous for animals like crab, shrimp and lobster when it come to hunting for food.
