Brrrr! How well do you think you would grow if you lived in a freezer? Adam Marsh, a marine biochemist at the University of Delaware, and colleagues Rob Maxson and Donal Manahan from the University of Southern California, have discovered an important reason why the pincushion-like Antarctic sea urchin (Sterechinus neumayeri) can function so well in the polar seas surrounding the Earth’s frozen continent.
The Antarctic sea urchin demonstrates a remarkable economy, a super energy-efficiency in its metabolism. Despite frigid water temperatures and little available food, its babies can synthesize proteins more efficiently than any other organism recorded to date. The scientists’ findings are reported in the March 9 edition of Science.
“All animals expend about 30% of their energy just turning over proteins,” says Marsh. “But the embryos and larvae of the Antarctic sea urchin can perform this vital metabolic process using 25 times less energy than the rest of us. That’s really amazing,” he notes, “especially considering the extreme environment in which these larvae live and an almost non-existent food supply.”
The Antarctic sea urchin resembles a red pincushion, about 5 inches in diameter, with long spines extending from its round shell. It lives on the seafloor and uses its spines and sucker-tipped tube feet to move about. Baby sea urchins are spawned during the summer months and take about a year to develop from embryo to larva to juvenile — a stage that is a miniature version of the adult.
To collect sea urchins for their study, Marsh and his colleagues traveled periodically to McMurdo Station, a research outpost on Ross Island, Antarctica. The scientists cut holes in the 8-foot-thick sea ice and inched down a tow rope into the freezing water wearing insulated diving suits that covered all but their faces. Their lips and cheeks would go numb after 60 seconds of exposure.
Once the sea urchins were collected from the seafloor, they were taken to McMurdo Station’s Crary Laboratory for experiments. On several occasions, the animals were flown back to the lab by helicopter. “The problem with collecting marine animals in Antarctica is not keeping them cold during the trip back to the lab but to keep the seawater in the coolers from freezing solid during the trip,” Marsh explains.
Housed in the lab in the cold water pumped in from McMurdo Sound, the female sea urchins were induced to spawn and the eggs were fertilized. The scientists then began measuring the changes in total metabolic rates as the embryos developed into larvae, along with corresponding changes in the rate of protein turnover, or metabolism. More than 10 million embryos were tested during the three-year project.
So what does identifying the most energy-efficient animal mean to the rest of us, besides making us feel metabolically inadequate?
“We know the Antarctic sea urchin can process proteins using less energy than anyone else,” Marsh says, “but we don’t know yet what mechanism allows the animal to do so much with so little. Finding the answer could yield some important benefits,” he notes. “For example, if you could incorporate this energy-efficiency into a fish, oyster, or clam, you could feed it less food and get the same growth rate. That kind of capability would be a great boon to aquaculture.”
Note: This research was funded by the National Science Foundation’s Office of Polar Programs. During this project, Adam Marsh was a postdoc at the University of Southern California, working with principal investigator Donal Manahan. Marsh joined the faculty of the University of Delaware College of Marine Studies in 2000.