LOW SUMMER TEMPERATURES - A POTENTIAL MORTALITY FACTOR FOR HIGH ARCTIC SOIL MICROARTHROPODS

Throughout the summers of 1999-94 the low temperature performance of s oil microarthropods at Ny Alesund, Spitsbergen (78 degrees 56'N 10 deg rees 53'E), was investigated. Species studied were the Collembola Hypo gastrura tullbergi (Schaffer), Onychiurus arcticus (Tullberg) and Onyc hiurus groenlandicus (Tullberg) and the mites Diapterobates notatus (T horell), Hermannia reticulata (Thorell), Camisia anemia Colloff and Ce ratoppia hoeli (Thor). The results show that: (i) The supercooling abi lity of these animals decreased rapidly on regaining activity in sprin g. For example, the supercooling point (scp) of H. tullbergi when heat extracted from frozen ground, decreased from -20 to -8 degrees C with in 4 h. Population sep profiles of all species determined throughout t he summer showed distinct bimodal distribution; (ii) starvation for 14 days, desiccation or a combination of both, resulted in little change in the mean scp of the collembolan O. arcticus; (iii) survival of the animals after a brief exposure to a sub-zero temperature was poor, in either humid or dry atmospheres. For example, 77% of H. tullbergi die d after cooling to -5 degrees C at 1 degrees C min(-1). Comparison wit h sep data indicates that animals died before they froze; (iv) all spe cies examined showed some locomotory ability at temperatures approachi ng -3 degrees C; (v) polyols occurred in low concentrations, although elevated levels of glucose were observed in early spring and late autu mn in O. arcticus; and (vi) soil temperature declined to -29.6 degrees C in the winter of 1992/93 and remained below zero for up to 289 days and the animals can be encased in ice for 75% of the year. Average da ily soil temperatures for July and August rarely exceed 8 degrees C an d were typically in the range 3-6 degrees C. Estimation of previous ye ars soil temperatures from screen temperature records indicate that Ju ly/August ground surface temperatures <0 degrees C occurred on 25 and 28 occasions between 1969-93 at the polar semi-desert and tundra heath sites respectively; but, that soil temperatures at a depth of 3 cm ar e buffered 0 degrees C are rarely encountered. The consequences for th e soil microarthropod fauna of such extended periods of low temperatur e and the effects of climate change on these species are discussed.