Abstract
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.
