Refining the risk of freezing mortality for Antarctic terrestrial microarthropods

In studies of three common, freezing susceptible, Antarctic microarthropods, the springtail Cryptopygus antarcticus and the mites Alaskozetes antarcticus and Halozetes belgicae, we report (i) the consequences on cold tolerance of cooling in contact with water, and (ii) the risk of freezing when held at temperatures above the typical freezing point (measured using standard techniques) for up to 12 h. The springtail showed no change in SCP distribution when in contact with freezing water while, in contrast, the mites showed clear shifts towards decreased cold tolerance, in addition to death of c. 33% of individuals during the freezing of the water. The springtail showed a bimodal SCP distribution, with the population divided into "high"(typically -8 to -12 degree C) and "low" (typically below -20 degree C) groups. Some animals held at temperatures above these values froze, over a timescale between minutes and several hours. These results highlight the danger of equating standard cold tolerance measures with mortality risk under more realistic water and thermal regimes.