Sea-ice microbial communities

Abstract

Being located in the most remote and climactically harshest regions of Earth, research on sea-ice and its primarily microbe-sized inhabitants has been steadily progressing over the last 30 years. Sea-ice, especially in the Antarctic, is exceptionally seasonally dynamic, and biological activity within sea-ice is thus physically forced in way that generates a community structure different to the underlying seawater. Sea-ice microbial communities (SIMCOs) contribute substantially to the total productivity of polar oceans and influence global energy budgets and atmospheric-oceanic interactions. In spring when ice extent is still close to maximal ice-associated algae bloom forming distinct banded assemblages living within the ice matrix. Bacterial growth accelerates when the algal bloom is well established. Sea-ice bacteria are often epiphytic and dependent on algal production. SIMCO can achieve very dense concentrations of cells that can lead to hypoxic pockets allowing denitrification and other processes. Together with algae sea, ice bacteria form a discrete microbial loop, which in turn supports allochthonous and autochthonous small metazoa, and by virtue of its vast extent collectively forms a major food source in polar oceans at higher trophic levels. The sea-ice SIMCO bacterial component, primarily members of classes Gammaproteobacteria, Alphaproteobacteria, and Flavobacteria, like the algae possesses a highly developed degree of psychrophily with the ability to multiply at subzero temperatures. It is one of the few environments, except the deep ocean, where true psychrophiles predominate. Within this extremely cold and very saline environment, algae and bacteria clearly thrive, even down to -20 °C. The myriad of specialized adaptations allowing survival in sea-ice brine channels represents an exciting research dimension that is not only ecologically very interesting but also astrologically and having biotechnological potential. With climate change, Antarctic and especially Arctic sea ice are perhaps the most threatened biomes on the planet, and thus, there is some urgency in the understanding of sea ice and preservation of its inhabitants.