Dissertation Abstract
Diversity and ecology of bacterial communities at the deep seafloor
Bienhold, Christina A 2011 https://www.mpi-bremen.de/en/Christina_Bienhold.html
Department of Biology and Chemistry, University of Bremen (Germany), 178 pp.
Understanding biodiversity and its distribution across space, time, and along environmental gradients, is crucial in order to assess the ecological functions of groups of organisms in the environment and gain insights into overall ecosystem functioning. In contrast to the distribution patterns of larger organisms, little is known about the structuring of bacterial communities in the environment. Today, molecular tools like fingerprinting or next-generation sequencing enable a time- and cost-effective, high-throughput processing of environmental samples to study bacterial diversity patterns. However, research on microbial community ecology is just starting to pick up pace, and entire ecosystems, such as the deep seafloor, remain largely uncharted. The deep sea represents the largest ecosystem on Earth and at the same time remains one of the least explored regions on our planet. Bacterial communities play an essential role for carbon and nutrient cycling in deep-sea sediments, and are thus an important component of benthic deep-sea ecosystems. Therefore, the specific investigation of bacterial diversity and its distribution at the deep seafloor in the context of environmental parameters were major objectives of this thesis.
In Chapter I, global-scale patterns of bacterial community composition in deep-sea surface sediments were explored. Strong distance-decay relationships and a high degree of endemism suggested a limited dispersal of benthic bacterial populations in the deep sea. In addition, potential members of a core deep-sea surface sediment community were identified.
Results presented in Chapter II describe the distribution of bacterial diversity at intermediate (10–3000 km) and large (>3000 km) scales. Both, geographic distance and environmental heterogeneity influenced bacterial diversity at these scales, indicating a complex interplay of local contemporary environmental effects and dispersal limitation.
The relationship between energy availability and bacterial diversity and activity was investigated at the regional scale (7–500 km) in Arctic Ocean deep-sea sediments (Chapter III). Phytodetritus input, as a proxy for energy availability at the deep seafloor, was evidenced to be an important driver of changes in bacterial diversity and activity along the investigated depth transects. The results indicate that bacterial communities may exhibit energy-diversity relationships comparable to the ones observed for macrofaunal deep-sea organisms. Furthermore, contrasting responses of individual taxa to changes in phytodetritus input suggested varying ecological strategies among bacterial groups, and may enable the classification of indicator taxa for certain environmental states.
Finally, the influence of a specific source of energy, i.e., wood, on the biogeochemistry and bacterial diversity at the deep seafloor was investigated using experimental wood deployments (Chapter IV). The deposition of wood at the deep seafloor presents a localized input of organic matter to an otherwise largely oligotrophic environment. Wood colonization experiments were deployed in the Eastern Mediterranean deep sea for one year, and revealed the development of sulfidic niches and the colonization of specialized communities at these large organic food falls.
In Chapter I, global-scale patterns of bacterial community composition in deep-sea surface sediments were explored. Strong distance-decay relationships and a high degree of endemism suggested a limited dispersal of benthic bacterial populations in the deep sea. In addition, potential members of a core deep-sea surface sediment community were identified.
Results presented in Chapter II describe the distribution of bacterial diversity at intermediate (10–3000 km) and large (>3000 km) scales. Both, geographic distance and environmental heterogeneity influenced bacterial diversity at these scales, indicating a complex interplay of local contemporary environmental effects and dispersal limitation.
The relationship between energy availability and bacterial diversity and activity was investigated at the regional scale (7–500 km) in Arctic Ocean deep-sea sediments (Chapter III). Phytodetritus input, as a proxy for energy availability at the deep seafloor, was evidenced to be an important driver of changes in bacterial diversity and activity along the investigated depth transects. The results indicate that bacterial communities may exhibit energy-diversity relationships comparable to the ones observed for macrofaunal deep-sea organisms. Furthermore, contrasting responses of individual taxa to changes in phytodetritus input suggested varying ecological strategies among bacterial groups, and may enable the classification of indicator taxa for certain environmental states.
Finally, the influence of a specific source of energy, i.e., wood, on the biogeochemistry and bacterial diversity at the deep seafloor was investigated using experimental wood deployments (Chapter IV). The deposition of wood at the deep seafloor presents a localized input of organic matter to an otherwise largely oligotrophic environment. Wood colonization experiments were deployed in the Eastern Mediterranean deep sea for one year, and revealed the development of sulfidic niches and the colonization of specialized communities at these large organic food falls.