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Climate Change Hitting the Sea's Little Guys Too

Graeme Stemp-Morlock
for National Geographic News
February 29, 2008
 
When it comes to climate change, polar bears and sharks may grab the bulk of the headlines—but it's the threat to the sea's tiniest creatures that has some marine scientists most concerned.

Malformed seashells show that climate change is affecting even the most basic rungs of the marine food chain—a hint of looming disaster for all ocean creatures—experts say.

Climate change could drastically reduce sea urchin populations in particular, according to Gretchen Hofmann, a marine biologist at the University of California, Santa Barbara.

The purple sea urchin is commonly found off the coast of Australia and Antarctica. It is an essential food source for many marine animals such as cod or lobster, as well as a common ingredient in sushi.

Hofmann is concerned because increasing amounts of atmospheric carbon dioxide are also raising the amount of the gas dissolved in ocean water. This makes the seas more acidic, decreasing the available amount of shell-forming calcium carbonate.

Future Ocean in a Box

To test the theory, Hofmann tested sea urchins in highly acidic water similar to what is predicted for the oceans.

"We checked if they can make the skeleton that forms their bodies, and yes it is formed," Hofmann said. "But it was shorter and stumpier—not the same shape—so they swim and move differently. Plus it comes at a cost, which is they are more sensitive to temperature."

Hofmann refers to this malformed skeleton and sensitivity to heat as "double jeopardy."

She went further than any previous research by analyzing the recently sequenced sea urchin genome to find out what genes were turning off and on under this new environmental stress.

"We wanted to ask them how they were doing and get a sense of their health and physiology," Hofmann said. "We found it caused their shell-forming genes to go up threefold, so their developing system was having to put more energy into making the skeleton and less into other things."

Hofmann presented her findings at the recent meeting of the American Association for the Advancement of Science in Boston, Massachusetts.

"Sea Butterflies" Next?

Scott Doney, a chemical oceanographer at Woods Hole Oceanographic Institute, said that Hofmann may have done "the same type of experiments [as previous researchers], but went beyond looking at the physiological impact of acidification on organisms.

"[Hofmann] used molecular biological tools to see what proteins are turned on or off as they experienced stress if the waters become really acidic," Doney said. "It is a validation in many ways of the physiological experiments others had done."

Doney compared sea urchins to homeowners who use all their cash to build the dwellings but don't leave any money for furniture.

"From the short-term experiments that have been running, the best indication is that likely the population as a whole will suffer dramatically," Doney said. "But, in addition to being a food source for things we eat, [sea urchins] are a harbinger of the damage we do to ecosystems."

Hofmann also pointed out that she just returned from Antarctica, where she was collecting samples of another first-rung-in-the-food-chain creature, the pteropod.

These miniscule creatures—which resemble snails flying through water—are sometimes referred to as sea butterflies.

They are an essential food source for many fish such as salmon, which feed penguins, seals, and other animals.

Hofmann plans to get a quick scan of the pteropod DNA sequence and then use that information to predict the impact climate change will have on these organisms.

"Pteropods are one of our lead organisms for understanding and predicting the effects of climate change. But they are a very unknown organism," she said.

"Pteropods are cold-adapted, so while we haven't tested it yet, we suspect their ability to tolerate temperature increases could be very narrow," Hofmann added.

"And they can't migrate anywhere to find colder water, so the pteropod situation could be even more dire than with sea urchins."

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