How sediment damages corals

Worldwide about 80% of the warm-water coral reefs have been harmed, and about 25% irreversibly damaged from direct human pressures. The effects of sedimentation on reef-building corals are well documented, as previous studies focused mostly on the coral response. The processes of how sediment actually damages corals, and the role of contrasting sediment properties have remained poorly understood. In this study we therefore focused on the sediments and investigated the harming processes. Our central hypothesis was that bacteria play a crucial role in the damage that sediment causes to corals. This thesis presents the advancement of two existing methods, data from mesocosm experiments, as well as field data, obtained with the new submersible microsensor system DOMS. This work revealed that harmful effects of sediment exposure on reef-building warm-water corals are tightly linked to sediment properties, primarily the percentage of silt grains, the organic matter content and the microbial activity, demonstrating that the exposure to organic-rich fine sediment is particularly dangerous for coral reefs, and that the demise of sediment-covered corals is mediated by microbial activity.