Finding the Estuaries Using Microbial Eukaryote Communities Along River to Sea Continuums in Hudson Bay, Canada.

The Greater Hudson Bay Marine region is fresher than other Arctic Seas, with high inputs of freshwater from rivers with large drainage basins. Hudson Bay is currently being impacted by both climate change and water regulation from large hydroelectric projects, but little is known about the microbial communities that are being impacted by changing hydrologic regimes. Here we specifically aimed to investigate the microbial eukaryote biodiversity and associated drivers of 3 river systems on two sides of Hudson Bay. Gradients in light, nutrients, temperature and salinity, influence microbial community structure, but these gradients are determined by geomorphology and up stream flow characteristics. In the Arctic the additional input of sea-ice melt within the basin will also influence salinity and temperature gradients. We identified microbial eukaryote assemblages using the V4 region of the rRNA 18S genes along the salinity gradient of two major inflows into Eastern Hudson Bay: The Nelson and the Churchill Rivers. These rivers are both highly stratified but exhibit strong hydrodynamic differences under the contrasting influence of river damming and estuarine geomorphology. Data was combined with a less detailed data set from the Great Whale River in Western Hudson Bay to identify coastal and river core communities. The microbial communities were classified along the salinity gradient to identify spatial patterns and factors potentially controlling the distribution of the major microbial eukaryotes, including potential and invasive (non- pan arctic) species in all samples. We found that river runoff was a source of heterogeneity and drove biodiversity differences among coastal marine communities. Specialist taxa identified in each coastal region were good indicators of local environmental conditions.