Chilling and freezing resistance of two interstitial polychaetes from a sandy tidal beach.

The two mesopsammal polychaetes, Hesionides arenaria and Trilobodrilus axi, show a relatively high resistance to cold temperatures in experiments. Great differences, however, between supercooled and frozen individuals exist. In chilling experiments T. axi is much less sensitive (no damage after 5 h at -12° C) than H. arenaria (50% mortality after 1 h at -7° C). The freezing resistance is essentially much less, but identical for the two species (100% mortality at -10° C after 1 h exposure). The differences in the supercooling resistance of the two species are in agreement with their geographic distribution and their seasonal migration behavior in the sandy beach locality.