Biological communities identified at the summit of Conical Seamount using the Alvin submersible include presumed biological coatings on carbonate chimney structures (no microbial studies were performed on the materials), limpets, and small high-spire gastropods (Fryer et al., 1990). Dives at the summit of South Chamorro Seamount with the Shinkai 6500 discovered and sampled three cold springs that support the growth of carbonate crusts and chimneys and communities of mussels, small tubeworms, gastropods, and galatheid crabs (Fryer, 1996a; Fryer and Mottl, 1997). Drilling at South Chamorro Seamount also revealed a remarkable extremophile microbial community living in the upper 30 meters below seafloor (mbsf) at a pH of 12.5, while generating carbonate alkalinity by oxidizing methane from the upwelling fluid and reducing sulfate from both the upwelling fluid and seawater (Shipboard Scientific Party, 2002; Mottl et al., 2003). The population is dominated by Archaea (Mottl et al., 2003) but also contains unique bacteria (Takai et al., 2005).
Takai et al. (2005) examined the culturability of bacteria in the serpentine muds at South Chamorro Seamount and identified a new species of Marinobacter (M. alkaliphilus). This new species predominantly flourishes in the shallow serpentine mud to ~2.95 mbsf, where pH levels in the pore fluids are ~10. Deeper in the serpentine muds, pH levels are too high for optimal growth conditions. The highest bacterial population at Site 1200 is at 0.05 mbsf, based on bacterial biomass estimation by phospholipids fatty acid (PLFA) analysis (Mottl et al., 2003), suggesting to Takai et al. (2005) that seawater infiltrating the serpentine mud is likely the source of inoculation of the mud with M. alkaliphilus and may explain why the species appears to be absent from the deeper microbial populations below 2.95 mbsf. The elevated pH of the pore fluids favors the survival of M. alkaliphilus over other bacteria derived from seawater, but the low temperatures of the near-surface muds (1.7°–1.9°C, below the limit for growth in the laboratory) suggest that the alkaliphilic species are either dormant or have extremely low growth rates (Takai et al., 2005).