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Microbial diversity and function of deep-sea manganese nodule ecosystems


Vonnahme,  Tobias R.
HGF MPG Joint Research Group for Deep Sea Ecology & Technology, Max Planck Institute for Marine Microbiology, Max Planck Society;

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Vonnahme, T. R. (2016). Microbial diversity and function of deep-sea manganese nodule ecosystems. Master Thesis, University of Bremen, Bremen.

Cite as: https://hdl.handle.net/21.11116/0000-0001-C339-3
Due to a constantly growing demand of minerals and the depletion of terrestrial resources alternative ways of mining are explored. Manganese nodules cover a large area of the abyssal plain in the oceans and are considered to become a valuable resource for deep-sea mining. The ecosystems and their services in manganese nodule fields are, however, hardly understood and the impacts of deep-sea mining on the environment are hard to predict. In 1989 a disturbance and recolonization experiment (DISCOL) was established to simulate the effects of deep-sea mining on these ecosystems. The current thesis is based on the disturbed DISCOL sites. It evaluates, for the first time, the potential effects of deep-sea mining on microbial activities and their community structure and functions. During the SO242/2 cruise sediment cores and nodules were sampled in different disturbed and undisturbed areas of the Peru Basin. A freshly disturbed track caused by an EBS, four microhabitats related to the initial DISCOL tracks, and reference areas were sampled, using a ROV or a MUC. The sediments were characterized by their color, phytopigments, porosity and cell numbers. The microbial activities were evaluated via measuring diffusive oxygen fluxes, extracellular enzymatic activities, DIC uptake rates, and the proportion of alive and active cells. The microbial communities and diversities were characterized via CARD FISH and 16S rRNA Illumina tag sequencing, and indicator taxa were identified. The thesis showed that the areas, where the reactive surface layer was removed are most affected, even after 26 years. Most measured parameters in these sites, stay close to values of the subsurface layer: The activities of OM related enzymes, respiration rates, DIC fixation rates, and the proportion of life and active cells are drastically reduced; Autotrophic metal oxidation appears to decrease drastically; The microbial community structure of potential autotrophs in these microhabitats is mainly characterized by nitrifiers, while autotrophs with different DIC fixation pathways are more characteristic for the reference area. In general, I conclude that deep-sea mining reduces microbial activities, and changes their community structure and consequently their function in the manganese nodule ecosystems for more than 26 years. Since microbes act as the bottom of a multi trophic food web, higher trophic levels may be indirectly affected by the same mechanisms.