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

Abstract

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.