Investigation of the distribution and activity of benthic microorganisms in coastal habitats

This dissertation thesis deals with temporal and spatial variations in bacterial activities and community structure in coastal sandy sediments of the temperate German Wadden Sea. The activities of the heterotrophic bacterial community were found to be strongly coupled to microphytobenthic primary productivity in this habitat and as such varied strongly with space and time. The vertical and temporal changes in bacterial activities were accompanied by significant shifts in bacterial community structure. While the spatial shifts could mainly be related to lateral variations and vertical gradients in microphytobenthos-associated labile organic carbon availability and redox potentials, temporal shifts were mainly stochastic and could not be related to any of the environmental parameters included in this study. The bacterial community was highly diverse and extremely dynamic with a replacement of 47% of operational taxonomic units over 2 years. The bacterial community structure did not reflect the strong seasonal patterns in bacterial activities, indicating a high redundancy in general ecosystem functions.