In this chapter, three main aspects of the interrelationship between gas volcanism and biota are discussed. The first aspect deals with the origin of methane. The second aspect concerns methane communities and “methane-derived” carbonate buildups“methane-derived” carbonate buildupsassociated with them. The third aspect relates to the influence of gas volcanism on benthic ecosystems. It is shown that methane in marine environments is generated by two dominant processes—biogenic and abiogenic. Biogenic methaneBiogenic methane is produced by methanogenic archaea (bacterial methanebacterial methane) or by the thermally-activated breakdown of larger organic molecules (thermogenic methanethermogenic methane). Abiogenic methaneAbiogenic methanehas its origin in the deep Earth. It moves by fluid flows rising upwards from the Earth’s lower crust to the seafloor through the sedimentary cover via cracks caused by tectonic movements. This abiogenic methane is also thermogenic, however, it is formed under much higher temperatures compared to the thermogenic methane of biogenic origin. All kinds of methane tend to migrate and mix in the subsurface. Identifying the relative contributions of each kind of methane to a given accumulation of this gas is a challenge. A number of indicators used to distinguish them are described in the chapter. An overview is provided of the modern concepts of methane-derived carbonates that form in areas where methane seeps develop as well as the role of biota in their formation on the bottom of the Black Sea. The diversity of relationships between degassing, carbonatization, and behavior of the Black Sea microbiotamicrobiota can be reduced to four types.