Differences between the bacterial community structures of first- and multi-year Arctic sea ice in the Lincoln Sea.

The Arctic sea ice composition is shifting from predominantly thick perennial ice (multiyear ice -MYI) to thinner, seasonal ice (first year ice -FYI). The effects of the shift on the Arctic ecosystem and macro-organisms of the Arctic Ocean have been the focus of many studies and have also been extensively debated in the public domain. The effect of this shift on the microbial constituents of the Arctic sea ice has been grossly understudied, although it is a vast habitat for a microbial community that plays a key role in the biogeochemical cycles and energy flux of the Arctic Ocean. MYI and FYI differ in many chemical and physical attributes (e.g. bulk salinity, brine volume, thickness and age), therefore comparing and contrasting the structure and composition of microbial communities from both ice types will be crucial to our understanding of the challenges that the Arctic Ocean ecosystem faces as MYI cover continues to decline. Here, we contend that due to the differences in abiotic conditions, differences in bacterial community structure will be greater between samples from different ice types than within samples from the same ice type. We also argue that since FYI is younger, its community structure will be closer to that of the surface sea water (SW). To test this hypotheses, we extracted DNA and used high throughput sequencing to sequence V1-V3 regions of the bacterial 16s rRNA gene from 10 sea ice samples (5 for each ice type) and 4 surface sea water (SW) collected off the shore of Northern Ellesmere Island, NU, CAN, during the month of May from 2010-2012. Our results showed that observed richness was higher in FYI than MYI. FYI and MYI shared 26% and 36% of their observed richness respectively. While FYI shared 23% of its observed richness with SW, MYI only shared 17%. Both ice types showed similar levels of endemism (61% of the observed richness). This high level of endemism results in the grouping of microbial communities from MYI, FYI, and SW to three distinct groups when looking at membership (jclass dissimilarity index, tested by AMOVA). However, when looking at composition (θYC dissimilarity index) while communities from MYI and SW samples still clustered as two distinct groups, communities from FYI samples show no significant clustering (tested by AMOVA).