Antarctic Creature's Growth Rate Mysteriously Doubles
The tiny animals studied, Cellarinella nutti, grows into stick-like forms and lives cemented to the seabed. Each year a band of growth is formed. The longer its food, marine algae called phytoplankton, is available the more it grows.
Credit: British Antarctic Survey

Small filter-feeding animals that look like branched twigs collected more than a century ago from Antarctica's Ross Sea reveal a mysterious increase in how fast the modern-day animals have been growing over the past two decades.

While the researchers can only speculate the cause right now, the amped-up growth makes the tiny organisms carbon collectors, potentially a positive thing for climate change.

Captain Robert Falcon Scott is best known as head of the second expedition to reach the South Pole, and who, with his team, died on the return trip in 1912. But unlike other polar explorers, he also made a variety of high-quality scientific collections, said David Barnes, a researcher with the British Antarctic Survey. [Gallery: Scientists at the Ends of the Earth]

"Now that people are very interested in change in the polar regions, those specimens have become incredibly valuable as the only source of information at that time," Barnes told LiveScience.com.  

These included samples of the tiny animals, a species of bryozoan called Cellarinella nutti, collected with data on the longitude, latitude and depth, Barnes said. Like trees, these creatures produce annual growth rings, giving researchers a window into how growth rates may have changed over time.

Scott's specimens, along with others, allowed Barnes and his collaborators to compare growth rates for the creatures living on the floor of the Ross Sea from 1890 to 2008.   

Like corals, most bryozoans secrete calcium carbonate to form their hard exoskeletons as they grow. The team found that growth rates, or the calcium carbonate each specimen acquired per year, remained roughly constant from 1890 through 1970, although there was a great deal of variability in the 1950s and 1960s. The next available data, from the 1990s to 2008, showed the bryozoans' growth rates doubled, so the animals were adding twice as much calcium carbonate per year.

The animals are most likely growing because more of their food – marine algae called phytoplankton – is available for longer periods, allowing them to consume — and grow — more, Barnes said. However, it's not clear why phytoplankton blooms are lasting longer in the Ross Sea, he said.

"This is not an area of Antarctica that is warming, and it's not an area that seems to be losing sea ice," Barnes said, noting that current measurements might overlook local changes in temperature or sea ice that are relevant to the bryozoans' growth.

Even though it appears that climate change near the South Pole may not be responsible for the recent surge in growth among these animals, their growth could have implications for climate change.

The bryozoans grow like a forest across the sea bed. Currents along the ocean bottom break them up and they become buried on the seafloor, taking the nutrients they contain, including the carbon, out of the food chain and the surrounding water. So, the more these creatures grow, the more carbon is locked away in the seafloor. This creates what is called a carbon sink.

Carbon sinks counteract the effects of humans' greenhouse gas emissions by removing some of the carbon humans are spilling into the atmosphere in the form of carbon dioxide. (Trees also create a carbon sink by sucking up carbon dioxide and sequestering the carbon in their wood, taking it — at least temporarily — out of the atmosphere.) 

The results appear in the Feb. 22 issue of the journal Current Biology.

You can follow LiveScience writer Wynne Parry on Twitter @Wynne_Parry.