Copepods are the most abundant metazoans in sea ice and can be found in dense numbers; over 1000 per litre of ice compared to less than 10 per litre in open water. Arctic ice samples often contain cyclopoid copepods including Cyclopina gracilis and C. schneideri which overwinter in the sea ice but spend ice free periods near the sea floor (Thomas, 2004).
Harpacticoid copepods (Fig. 2) are often found in both Arctic and Antarctic ice and are associated with surface sediments on the sea floor (Thomas and Dieckmann, 2003).
Copepods are more abundant in the Antarctic than the Arctic, in the Antarctic they are the dominant grazers with three species (Stephos longipes, Paralabidocera antarctica and Drescheriella glacialis) dominating the sea ice fauna (see life cycles for more information on these species).
Adaptations to survive the harsh conditions of sea ice include energy storage in the form of lipids for periods of short food supply (Martynova et al. 2009). Copepods that feed throughout the winter, such as those within the sea ice use triacylglycerol as their lipid store (Thomas, 2004).
Copepods are generally found in the porous bottom layers of sea ice, as they cannot alter their body shape to squeeze into brine channels smaller than themselves (Thomas, 2004).