Reaktion benthischer mikrobieller Tiefsee-Gemeinschaften auf den Eintrag von partikulärem organischen Material: In situ Experimente in der Framstrasse (Arktischer Ozean)

This thesis aims at achieving deeper insights into the ecological functioning of heterotrophic microbial communities in high northern latitude deep-sea sediments, i.e. their structural and functional response to a sudden large input of particulate organic matter (POM).Three in situ studies, each divided into a short- (seven days) and long-term experiment (one year), were carried out by using a Sediment Tray Free Vehicle (STFV) which was deployed in the Arctic Ocean at the experimental site of the deep-sea long-term observatory HAUSGARTEN (Fram Strait, 2500 m water depth). Special emphasis was placed on the enrichment of deep-sea sediments with chitin as one of the most important biopolymer in aquatic ecosystems. Additionally, experiments were carried out in association with different sediment types (deep-sea sediments, glass beads, coarse sand) to assess how variations in sediment characteristics (e.g. particle size, particle shape, organic carbon content) affect the microbial response to POM supply.Different microbial parameters (cell number, biomass, hydrolytic enzyme potential) were measured and bacterial community composition was determined by using the fingerprint method of terminal-restriction fragment length polymorphism (T-RFLP).Results evidenced clear chitin-dependent response of benthic microbial communities in the deep Arctic Ocean and underlined their important role in recycling this highly insoluble organic substrate. Their functional in situ response following a large chitin input may be triggered by an initial change in community structure before efficient utilisation of chitin compounds can be made. Sediment type was found to be a significant factor influencing enzymatic activity and structure of deep-sea microbial communities. Overall, findings from these in situ studies demonstrated the important role of environmental conditions such as POM availability for driving microbial functioning and diversity at the Arctic deep seafloor

Response of deep-sea benthic microbial communities to particulate organic matter supply : in situ experiments in the Fram Strait (Arctic Ocean).

This thesis aims at achieving deeper insights into the ecological functioning of heterotrophic microbial communities in high northern latitude deep-sea sediments, i.e. their structural and functional response to a sudden large input of particulate organic matter (POM).Three in situ studies, each divided into a short- (seven days) and long-term experiment (one year), were carried out by using a Sediment Tray Free Vehicle (STFV) which was deployed in the Arctic Ocean at the experimental site of the deep-sea long-term observatory HAUSGARTEN (Fram Strait, 2500 m water depth). Special emphasis was placed on the enrichment of deep-sea sediments with chitin as one of the most important biopolymer in aquatic ecosystems. Additionally, experiments were carried out in association with different sediment types (deep-sea sediments, glass beads, coarse sand) to assess how variations in sediment characteristics (e.g. particle size, particle shape, organic carbon content) affect the microbial response to POM supply.Different microbial parameters (cell number, biomass, hydrolytic enzyme potential) were measured and bacterial community composition was determined by using the fingerprint method of terminal-restriction fragment length polymorphism (T-RFLP).Results evidenced clear chitin-dependent response of benthic microbial communities in the deep Arctic Ocean and underlined their important role in recycling this highly insoluble organic substrate. Their functional in situ response following a large chitin input may be triggered by an initial change in community structure before efficient utilisation of chitin compounds can be made. Sediment type was found to be a significant factor influencing enzymatic activity and structure of deep-sea microbial communities. Overall, findings from these in situ studies demonstrated the important role of environmental conditions such as POM availability for driving microbial functioning and diversity at the Arctic deep seafloor

Investigations of artificial sediments from two deep-sea in situ recolonization experiments deployed for one year at the central HAUSGARTEN station IV during ARK-XIX/3c

Commercial exploitation and abrupt changes of the natural conditions may have severe impacts on the Arctic deep-sea ecosystem. The present recolonisation experiment mimicked a situation after a catastrophic disturbance (e.g. by turbidites caused by destabilized continental slopes after methane hydrate decomposition) and investigated if the recolonisation of a deep-sea habitat by meiobenthic organisms is fostered by variations innutrition and/or sediment structure. Two "Sediment Tray Free Vehicles" were deployed for one year in summer 2003 at 2500 m water depth in the Arctic deep-sea in the eastern Fram Strait. The recolonisation trays were filled with different artificial and natural sediment types (glass beads, sand, sediment mixture, pure deep-sea sediment) and were enriched with various types of food (algae, yeast, fish). After one year, meiobenthos abundances and various sediment related environmental parameters were investigated. Foraminifera were generally the most successful group: they dominated all treatments and accounted for about 87% of the total meiobenthos. Colonizing meiobenthos specimens were generally smaller compared to those in the surrounding deep-sea sediment, suggesting an active recolonisation by juveniles. Although experimental treatments with fine-grained, algae-enriched sediment showed abundances closest to natural conditions, the results suggest that food availability was the main determining factor for a successful recolonisation by meiobenthos and the structure of recolonised sediments was shown to have a subordinate influence

Effects of dropstone-induced habitat heterogeneity on Arctic deep-sea benthos with special reference to nematode communities

During an expedition to the deep-sea long-term observatory HAUSGARTEN in the eastern Fram Strait in summer 2003, the availability of a Remotely Operated Vehicle allowed a targeted sampling of surface sediments around a relatively large dropstone (0.9 m2) to determine suspected differences in community structure and dynamics of nematode assemblages in relation to the confined flow regime and patchy food availability in the immediate vicinity of the stone. The almost rectangular dropstone was about 150 cm in length, 60 cm in width, and up to 15 cm in height. Small-scale current measurements around the dropstone using a MAVS-3 acoustic current meter exhibited a rather complex pattern. A computational fluid dynamics simulation revealed areas of constantly flowing near-bottom currents as well as the generation of vortices in certain areas around the dropstone. Concentrations of biogenic compounds in the sediments surrounding the dropstone generally followed the complex flow pattern. The differences in physical and biochemical conditions around the dropstone were reflected in species composition and diversity, trophic structure and life-history traits of the nematode communities, and to a lesser extent in their total abundance and biomass