Nematodes (Fig.3) are mainly found in the Arctic, with only one species currently recorded in the Antarctic (Geomonhystera glaciei). All nematodes found in sea ice belong to the Monohysteroidea; they have not been described in underlying sediment and so are probably confined to the ice (Thomas and Dieckmann, 2003)
The Monohysteroidea is a super family containing members that live in rotting seaweed, marine sediments (with euryhaline conditions) and relatively dry soils; suggesting that representatives of this family are pre-adapted to living in the extreme habitat of sea ice with widely fluctuating environmental conditions (Tchesunov and Riemann, 1995). The special characteristics the family posses to live in such conditions are:
- Production of sticky secretions which helps with adhesion to surfaces
- Many species have a high tolerance to salinity within the range found in brine channels.
- Some species are very productive and have comparatively short reproduction cycles (Riemann and Sime-Ngando, 1997).
Three nematode species have been identified in sea ice, they are Theristov melnikovi. Cryonema crassum and C. tenue (Tchesunov and Riemann, 1995).
Theristov melnikovi is usually found in the bottom 3m of drifting pack ice; samples collected by Tchesunov (1986) in April consisted of juveniles living around 260cm from the bottom of the ice in denser numbers than further down nearer the ice-water interface. No diatom frustules were present in the digestive system of the juveniles, (or of any of the adults collected in any study) despite being found in high abundance and so it is thought that the juveniles over winter in a non-feeding stage (Tchesunov, 1986), or that this species feeds on dissolved organic matter which is found in brine channels (Tchesunov and Riemann, 1995).
The guts of Cryonema crassum have been found filled with various food items, including cells of a fungal origin and prey nematodes such as juvenile Theristov melnikovi (Tchesunov and Riemann, 1995).