Using differential scanning calorimetry to study freezing in a euryhaline aquatic invertebrate

Differential scanning calorimetry was used to study the cryobiological characteristics of nauplii of the euryhaline aquatic brine shrimp Artemia saline acclimated to three salinities (5, 35 and 70‰°). There was no significant difference in the supercooling points (SCP) or freezable water contents of samples from the three salinities: Mean SCP values ranged from -21 to -22.5°C. Mean melt onset temperatures and melting points differed significantly with samples acclimated to 5‰°having considerably higher melting points than those from 35 or 70‰°. These results are discussed in relation to the hyper-hypo ionic osmoregulation shown by Artemia and compared with data for the harpacticoid copepod Tigriopus brevicornis, which is an osmoconforming species. The study emphasizes how the osmotic physiology of such a euryhaline invertebrate affects its supercooling ability and hence its survival in freezing conditions.