The importance of sea ice for exchange of habitat-specific protist communities in the Central Arctic Ocean

Sea iceis one of the main features influencing the Arctic marine protistcommunity composition and diversity in sea iceand sea water. We analyzed protistcommunities within sea ice, melt pondwater, under- icewater and deep-chlorophyll maximumwater at eight sea icestations sampled during summer of the 2012 record sea iceminimum year. Using Illumina sequencing, we identified characteristic communities associated with specific habitatsand investigated protistexchange between these habitats. The highest abundance and diversity of unique taxa were found in sea ice, particularly in multi-year ice(MYI), highlighting the importance of sea iceas a unique habitatfor sea ice protists. Melting of sea icewas associated with increased exchange of communities between sea iceand the underlying water column. In contrast, sea iceformation was associated with increased exchange between all four habitats, suggesting that brine rejectionfrom the iceis an important factor for species redistribution in the Central Arctic. Ubiquitous taxa (e.g. Gymnodinium) that occurred in all habitatsstill had habitat-preferences. This demonstrates a limited ability to survive in adjacent but different environments. Our results suggest that the continued reduction of sea iceextent, and particularly of MYI, will likely lead to diminished protistexchange and subsequently, could reduce species diversity in all habitatsof the Central Arctic Ocean. An important component of the unique sea ice protistcommunity could be endangered because specialized taxa restricted to this habitatmay not be able to adapt to rapid environmental changes.