The algae living in the pack ice is subjected to both extreme high and extreme low salinities. Within the pack ice the brine solution can be up to 150 whereas normal seawater salinities are around 35 in the Southern Ocean whilst on the surface of the ice in the melt pools, the salinity can be extremely low, approaching that of freshwater. The photosynthetic pigments found in ice algae work best between salinities of 35-50 and outside of this range, algal growth will be inhibited (Manes & Gradinger 2009).
Algae adapt to hypersaline conditions by increasing concentrations of osmolytes to prevent dehydration and to hyposaline conditions by reducing the concentration. This maintains the osmotic potential between the brine solution and the internal media in the cells and prevents cells bursting or shrinking (Thomas & Dieckmann 2002).
In studies on bacteria, high salinity only affects growth rate when combined with low temperature. Lipid packing was increased in high salinities, at both high and low temperature and increased branched chain fatty acids at low salinities; both of these mechanisms help to keep the cell membranes stable in fluctuating salinities and are likely to be used as mechanisms for algae (Nichols et al. 2000).
The algae have enzymes that are adapted to work over a range of salinities so that metabolic processes are not slowed and membrane composition is regulated (Nichols et al. 2000, Thomas & Dieckmann 2002).