Life cycles and population dynamics of enchytraeids (Oligochaeta) from the High Arctic

We report the results of the first study of the population dynamics and life cycles of Arctic enchytraeid populations. Sampling was undertaken in a Salix heath in Adventdalen, Svalbard, during one summer and the succeeding spring. In addition, a Cassiope heath at a more northerly site close to Ny-Alesund, Svalbard, was sampled twice. The Arctic enchytraeids were generally smaller at maturity than their temperate-zone relatives. The three most numerous species in the Salix heath, Henlea perpusilla, Henlea glandulifera, and Bryodrilus parvus, hatched from cocoons in early summer and attained adult size early in their second summer. A few H. perpusilla and H. glandulifera reached mature size in their first summer; since the summer of investigation was unusually cold, these species may have a 1-year life cycle in warmer years. Life cycles were apparently longer in the Cassiope heath than in the Salix heath. Henlea perpusilla, H. glandulifera, and B. parvus produced eggs throughout the summer in the Salix heath, though hatching was restricted to early summer. Therefore, the hypothesis that cocoons require a cold period to hatch was tested in a laboratory experiment. When soil containing cocoons was incubated at -5 degreesC for 3 weeks, a significant increase in juveniles was demonstrated for H. perpusilla and Bryodrilus diverticulatus compared with soils kept at constant summer temperatures. This is the first time that breaking of dormancy by an external stimulus has been demonstrated in enchytraeid cocoons.