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Environmental influences shaping microbial communities in low oxygen, highly stratified marine embayment

R. R. P. Da Silva*, C. A. White, J. P. Bowman, E. Raes, A. Bisset, C. Chapman, L. Bodrossy, D. J. Ross

*Corresponding author:

ABSTRACT: Microbial communities in the marine environment drive biogeochemical and nutrient cycles. However, microbial composition and therefore their role in ecosystems is likely to be strongly influenced by the environment. Here we examine Macquarie Harbour, a highly stratified system located on the west coast of Tasmania, Australia, to determine environmental factors driving the microbial diversity. Water was sampled along spatial and environmental gradients to examine the structure and composition of the microbial communities using high-throughput sequencing. Spatial distribution of the communities was found to be homogenous throughout the harbour’s surface, although different from riverine and oceanic samples. In contrast, the distribution and composition of microbial communities varied with depth-related changes in salinity and oxygen. Prokaryotes associated with riverine and brackish waters dominated the oxic surface waters. Phytoplankton metabolite-related bacteria and nitrite oxidizers were abundant at the halocline, whereas microbes linked to the consumption of organic matter, nitrogen, and sulphur metabolization inhabited the hypoxic bottom waters may acting as major players in oxygen consumption throughout harbour’s water column. This study provides valuable insights to the microbial community ecology inhabiting a semi-enclosed and highly stratified environment and will improve our knowledge on how bacterial and archaeal distribution may be influenced by a changing environment.