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Coastal and Estuarine Studies




Salt marsh microbial ecology: Microbes, benthic mats and sediment movement

R. J. Aspden, S. Vardy, and D. M. Paterson

Salt marsh systems are important in sustaining the ecology of coastal zones. In modern ecological terminology, the processes that occur within an ecosystem that can be judged as beneficial to man are known as “Ecosystem Services”. The major ecosystem services that salt marshes provide include: a habitat that serves as a nursery ground for birds and fish; a buffering system that mediates the erosive force of the ocean; and a site of carbon fixation that sustains the coastal food web. Salt marsh systems are very obviously dominated by halophytic angiosperms but the sediment between their stems serves as a rich substratum for microbial growth and development. This environment may appear harsh and uncompromising since the fine sediments of the marsh are often anaerobic within a few millimetres of the sediment surface and are subject to periods of tidal exposure and desiccation. Nevertheless, a wide diversity of microbial forms have become adapted to exploiting this harsh environment. The upper layers of sediment are inhabited by an assemblage of oxygenie phototrophs, which are replaced by anoxygenic phototrophs, and then heterotrophic forms with increasing depth in the sediment. This layering of microbial assemblages may take place over a few millimetres and establishes a microbial system characterised by extreme gradients. These microbial assemblages provide vital “services” of carbon fixation and nitrogen fixation while also acting to mediate the physical dynamics of the sediment through enhancing sediment capture and retention among the marsh plants. The microbial assemblages of salt marshes are therefore key to the overall meta-bolism and ecosystem services of the system. However, the study of these highly spatially-constrained assemblages presents real logistic difficulties and the final part of this review introduces a number of modern techniques employed to measure their properties while retain their natural structure and formation.

Citation: Aspden, R. J., S. Vardy, and D. M. Paterson (2004), Salt marsh microbial ecology: Microbes, benthic mats and sediment movement, in The Ecogeomorphology of Tidal Marshes, Coastal Estuarine Stud., vol. 59, edited by S. Fagherazzi, M. Marani, and L. K. Blum, pp. 115–136, AGU, Washington, D. C., doi:10.1029/CE059p0115.

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