Arctic vs. Antarctic
Both the Arctic and Antarctic have sea-ice communities; however there are differences between them. The Arctic pack ice has an integrated abundance of sea ice meiofauna of 1.3 to 223.3 x103 organisms m-2 sea ice and 0 to 320 x103 organisms m-2 sea ice in Antarctica (Gradinger, 1999). Arctic regions are multi-year ice habitats and so organisms often complete life cycles without being released from the sea ice (autochthonous) . This differs from the Antarctic where sea ice is more ephemeral and so organisms must survive in the water for periods of the year (allochthonous). Because of this the Arctic is home to more characteristically endemic ice species (Gradinger, 2001) which have not had the opportunity to evolve in the Antarctic (Thomas and Dieckmann 2003). As well as endemic ice species, other organisms are present that migrate. Examples in Arctic pack ice are species where the adults live in the benthos and their meroplankton inhabits the sea ice (in shallow, coastal areas) such as crustaceans, molluscs and benthic polychaetes (Gradinger, 2001).
Table 1: Arctic vs. Antarctic Sea Ice Environments (Adapted from Gradinger, 2001).
Sea Ice Metazoans
The composition of Sea ice fauna differs between the Arctic and Antarctic (Table 1). The largest metazoans in the Arctic sea ice are Nematodes Rotifers and Turbellarians whereas in the Antarctic, Nematodes and Rotifers appear to be missing (Gradinger, 2001); here Copepods and Acoel Turbellarians dominate. This difference in composition is not yet understood and is an area of continued research. As well as metazoans that live in the sea ice, larger animals (such as euphausiids and amphipods) live in close association in the under ice habitat (Thomas and Dieckmann 2003).
The following sections summarize the known facts about the main sea ice inhabiting (sympagic) metazoans (Copepods, Nematodes, Turbellarians and Rotifers).