Implications of ocean acidification for microbial life and for microbial interactions

Ocean acidification (OA) is a major threat to marine systems. Very little is known about OA effects on microbial communities and the services they provide to the ecosystem. Here, shallow-water hydrothermal CO2 vents in a tropical coral reef were investigated as model system to provide an ecosystem perspective on OA effects on the diversity and function of microbial communities, as well as interactions with other reef organisms. In conclusion, microbial communities, functions and interactions were fundamentally altered at the CO2 vents. However, the strength of the influence of the CO2 vents seemed to depend on the investigated reef environment. The changes in microbial communities and processes may contribute to a general decline of the reef ecosystem at hydrothermal CO2 vents. This thesis offers new insights into microbial life at shallow-water hydrothermal CO2 vents, as well as predictions about potential OA impacts. Yet, it also emphasizes the challenge of estimating future OA effects based on observation at OA analogues that exhibit a high environmental complexity such as shallow-water hydrothermal CO2 vents.