Reduced large-scale beta-diversity and changes in metapopulation patterns of sediment bacterial communities following a major inflow into the Baltic Sea

The Baltic Sea is heavily affected by eutrophication caused by nutrient overload, climate, and infrequency in major inflow events, resulting in widespread areas of oxygen depleted waters and sediments. A Major Baltic Inflow event (MBI) brings saline and oxygenated Atlantic Ocean water into the Baltic Sea, as occurred in 2014. Using a theoretical framework based on metapopulation and metacommunity theory we predicted a transition of the sediment bacterial community after the MBI, from a more heterogeneous community pattern driven by local colonisation-extinction dynamics towards a more pronounced environmental gradient but with reduced beta-diversities. Community diversity patterns before and after the MBI were investigated by 16S rRNA gene sequencing of samples from 42 Baltic Sea environmental monitoring stations. Results showed strong metapopulation dynamics with many satellite and few core taxa. NMDS-ordination showed distinct geographical clustering. After the MBI, alpha-diversity increased, beta-diversity decreased and a significant distance-decay relationship developed. Changes in community composition correlated significantly with changes in oxygen and salinity from 2010 to 2015. Our results indicate strong metapopulation and metacommunity structuring of sediment bacterial diversity and composition in the Baltic Sea and how movements of large-scale water bodies affect bacterial communities through changes in large-scale environmental gradients and dispersal patterns.
As manuscript in dissertation.