Sea ice is an extensive ecosystem covering 5% of the Northern Hemisphere and 8% of the Southern Hemisphere at its maxima (Horner et al. 1992). Within this sea ice is a rich assemblage of biological life from bacteria and diatoms through to Metazoans. Temperatures in sea ice range from -1.97 oC at the ice-water interface to -20 oC in the upper layers which are subject to atmospheric influence (Thomas et al. 2008).
As well as temperature, organisms in sea ice have to cope with increased salinity. When ice freezes the salt is forced out of the ice matrix in the form of brine, which can have salinity levels in excess of 200, the same organisms are also exposed to melting ice water with salinities close to 0 (Thomas, 2004). The brine expelled from the ice forms channels (Fig.1) within the ice matrix, these channels and pores have large surface areas for attachment of organisms (Ewert, 2010).
It is estimated that there is more liquid brine in all of the sea ice in the world than in 4 times the amount of water in all of the worlds rivers (Ewert, 2010) meaning brine channels provide a substantial habitat area. The channels have a diameter ranging from a few micrometers to a few centimetres (Weissenberger et al. 1992) so space is another limiting factor to survival.
Light levels are also generally low (especially as most biological activity is found in the bottom few centimetres of ice). This light level is subject to change due to the movement of snow on the surface of the ice .The environmental conditions present in sea ice are of a constantly changing gradient, the most stable conditions are found at the bottom of the ice pack, which is buffered by the surrounding water; here temperatures are close to melting point at 1.97 oC (Thomas et al. 2008). This means salinity is lower and brine channel volume is higher, allowing larger metazoans to inhabit this space. Most biological life is found here.
Despite the temperatures, salinity, light conditions and space available, sea is not an extreme environment for the organisms that inhabit it. Physiological and life history adaptations (often involving seasonal changes in sea ice and incorporation into sea ice) allow life forms to thrive in these extremes. Complex assemblages of Bacteria, Diatoms, Protists, Algae and Metazoans such as Nematodes, Copepods, Turbellarians and Rotifers (Thomas and Dieckmann, 2002) use the sea ice habitat for all or part of their life.
The Aim of this Blog is to provide a summary of Metazoans in sea ice; I will provide basic information on the main fauna found in both Arctic and Antarctic ice and talk about them in the context of life cycles, changes in community structure and discuss current theories of how they enter the sea-ice habitat.