tardigrade survival frozen
Tardigrade reanimated after being frozen for 30 yearsTsujimoto et al. 2016 Cryobiology photo by Megumu Tsujimoto (NIPR

Tardigrades have been revived after being frozen in Antarctic moss for 30 years. As well as being successfully re-animated, researchers found the water bears were able to successfully reproduce following their deep-freeze stint.

Researchers from the National Institute of Polar Research in Tokyo were examining tardigrades retrieved from a frozen moss sample collected in Antarctica in 1983. Previously, the longest recorded time a tardigrade has been revived from being stored in frozen conditions was eight years.

Tardigrades are able to survive in extreme conditions because they can shut down their metabolic activities – an ability known as cryptobiosis. On Earth, they can survive huge doses of radiation, intense pressures and even being dried out. They are so hardy they can even survive in the vacuum of space.

In the latest study, published in the journal Cryobiology, scientists said long-term survival has been one of the most-studied characteristics of nematodes, tardigrades and rotifers. The tardigrades studied had been storied at -20C for more than three decades. This included two individuals and one egg.

In May 2014, the tardigrades, measuring 0.2mm in length, were defrosted at 3C for one day then soaked in water for another 24 hours. They were reared on plates with algae provided as food. One of them died 20 days after rehydration, but the other individual went on to reproduce successfully – although the time it took for its eggs to hatch was far longer than normal.

The egg that had been frozen hatched and also went on to reproduce with no obvious signs of abnormalities. "We recorded recovery of two individuals and development of a separate egg of the Antarctic tardigrade, Acutuncus antarcticus, providing the longest records of survival for tardigrades as animals or eggs," they wrote.

They said possible damage that had accumulated during their 30 years on ice was indicated by the long recovery times and the time it took for the individuals' eggs to hatch, but added that further study is needed to improve our understanding of the long-term survival of tardigrades.

"Further, more-detailed studies using quantitative analysis with greater replication under a range of controlled conditions will improve understanding of mechanisms and conditions underlying the long-term preservation and survival of animals," they concluded.