Publication outline

In the following five chapters I will focus mainly on microbial communities in the sediment at the CO2 seeps in Papua New Guinea, presenting first a description of the environmental conditions in the sediment coupled with information on microbial and meiofaunal abundance and major metabolic processes. Subsequently, I will describe the microbial communities in the sediment in more detail, focusing on environmental factors that may influence community structure, trends in taxonomic community composition, and the functional potential of the microbial communities in relation to biogeochemical measurements. I will end with two pilot studies describing the bacterial and eukaryotic biofilm community on seagrass leaves and the bacterial community on settlement tiles exposed to the pH gradient created by the CO2 seeps in the water column.

Chapter 1: Sediment biogeochemistry at hydrothermal CO2 seeps within a coral reef

Artur Fink, Katja Guilini, Christiane Hassenrück, Anna Lichtschlag, Sergey M. Borisov, Dirk de Beer

Limnology and Oceanography (submitted).

This study investigates physico-chemical parameters in the sediment at volcanic CO2

seeps as well as the abundance of benthic meio- and microfauna and remineralization processes. It shows that reductions in permeability caused by OA-driven dissolution of reef carbonates may decrease the biocatalytic filtration function of future reef sediments.

Furthermore, the study emphasizes that sediments at volcanic CO2 seeps can be affected by factors other than CO2, thus highlighting the need for comprehensive measurements of environmental parameters within the sediments.

The study was designed by A. Fink and D. de Beer. K. Guilini provided meiofauna data.

C. Hassenrück contributed data on microbial cell counts. A. Lichtschlag provided pore water data. S. Borisov was involved in the measurements of oxygen consumption rates.

All co-authors were involved in data interpretation and discussion as well as

proof-26

reading of the manuscript. This chapter is included in this thesis to provide background information for chapters 2 and 3.

Chapter 2: Quantification of the effects of ocean acidification on sediment microbial communities in the environment: the importance of ecosystem approaches

Christiane Hassenrück, Artur Fink, Anna Lichtschlag, Halina E. Tegetmeyer, Dirk de Beer, Alban Ramette

FEMS Microbiology Ecology (in press).

This study used molecular and statistical methods to quantify the influence of various environmental parameters on microbial communities in the sediment along a pH gradient at CO2 vents in Papua New Guinea. It was shown that pH was among the factors significantly, yet not mainly, explaining changes in microbial community composition, and that therefore pH variation may often not be the primary cause of microbial changes when sampling is done along complex environmental gradients. Furthermore, the study discusses the potential for bacterial and archaeal taxa affected by the CO2 vents to alter biogeochemical cycles in the sediment.

The study was designed by C. Hassenrück and A. Ramette. C. Hassenrück was involved in sample collection, laboratory work, data analysis, and manuscript preparation. A. Fink and A. Lichtschlag contributed biogeochemical data and provided input for the manuscript preparation. H. Tegetmeyer performed the DNA sequencing. D. de Beer and all other co-authors contributed to data interpretation and discussion as well as proof-reading of the manuscript.

Chapter 3: Metatranscriptomic and biogeochemical investigations of sediment microbial processes at a shallow-water hydrothermal CO2 vent in Papua New Guinea

Christiane Hassenrück*, Artur Fink*, Pierre Offre, Pier Luigi Buttigieg, Halina E.

Tegetmeyer, Alban Ramette, Dirk de Beer

Frontiers in Aquatic Microbiology (in preparation).

27

This study provides an overview of microbial processes involved in major element cycles and how they may be affected by CO2 venting. The active microbial community as well as metabolic rates are investigated using molecular and biogeochemical methods focusing on the carbon, sulfur and nitrogen cycle. Furthermore, hypotheses for future research on microbial processes at shallow-water hydrothermal CO2 vents are presented.

The study was designed by C. Hassenrück and A. Fink, who conducted the sample collection, laboratory work and data analysis. H. Tegetmeyer performed the DNA and RNA sequencing. P. Offre and P. Buttigieg were involved in the analysis and interpretation of the metagenomic and metatranscriptomic data. A. Ramette, D. de Beer and all other co-authors contributed to data interpretation and discussion as well as proof-reading of the manuscript.

* The manuscript was prepared by A. Fink and C. Hassenrück as joint first authors.

Chapter 4: Seagrass biofilm communities at a naturally CO2-rich vent Christiane Hassenrück, Laurie C. Hofmann, Kai Bischof, Alban Ramette

Environmental Microbiology Reports 7: 516–525.

This study uses molecular methods to describe the bacterial and eukaryotic biofilm community associated with the leaves of the seagrass Enhalus acroides growing at a coral reef under ambient conditions and at a CO2 vent. An increased relative sequence abundance of bacteria associated with coral diseases was detected at the CO2 vent, as well as a decreased diversity of crustose coralline algae. The result suggest a potential role of seagrasses as vectors of coral pathogens, thus supporting predictions about decreased reef health under increased CO2 conditions.

The study was designed by C. Hassenrück and L. Hofmann, who also completed the sampling and laboratory work for the characterization of the microbial communities. L.C.

Hofmann measured carbon and nitrogen content of the seagrass leaves as well as epiphyte cover. C. Hassenrück conducted the data analysis and prepared the manuscript.

K. Bischof, A. Ramette and all other co-authors contributed to data interpretation and discussion as well as proof-reading of the manuscript.

28

Chapter 5: Bacterial biofilm composition on settlement tiles along natural pH gradients at two CO2 seeps in Papua New Guinea

Christiane Hassenrück, Katharina Fabricius, Alban Ramette

In preparation.

This study used a high sample throughput molecular fingerprinting approach to characterize the bacterial community on settlement tiles along two natural pH gradients.

The results suggest that changes in seawater pH did not have a strong impact on the development of the bacterial biofilms on settlement tiles, and that other abiotic and biotic factors, such as light exposure or close interactions with other organisms on the settlement tiles, may be more important in shaping bacterial biofilm communities.

This study was designed by K. Fabricius. C. Hassenrück completed the laboratory work and the data analysis related to the characterization of the microbial community. These results are presented here in a short report prepared by C. Hassenrück. K. Fabricius and A. Ramette contributed to data interpretation and discussion as well as proof-reading of the report.

29