Stoichiometry of Metabolite-Derived Particulate Organic Carbon and Nitrogen at Axial Seamount in the Northeastern Pacific Ocean

Abstract

Hydrothermal vents support dense biological communities through the nutrients and minerals they provide to otherwise barren benthic environments. In this study, particulate organic carbon and nitrogen ratios were calculated from metabolite concentrations in water collected near two hydrothermal vents within Axial Seamount's caldera to assess differences in metabolite production and preferential nutrient uptake relative to samples taken at the chlorophyll maximum and deep sea. These ratios were also compared to the modernly accepted expected stoichiometry of 163C:22N (7.409), to determine how C:N ratios at hydrothermal vents compare to ratios expected in the surface ocean. A metabolomic analysis of the fifteen most abundant metabolites at each sampling site revealed four common metabolites in support of a core metabolism. However, unique metabolites were observed in addition to these commonalities, showing the distinctive biological processes essential to life at environmental extremes. C:N ratio analysis revealed significant carbon limitation and excessive nitrogen in sites that would be expected to have greater biological activity such as at the local chlorophyll maximum and near hydrothermal vents. These biologically dense sites each presented ratios indistinguishable from each other (4.62 and 4.37, respectively). The site at depth within the caldera and with no vent influence displayed a relatively higher ratio, confirming signals of preferential diets, energetic dynamics, and nutrient availability at hydrothermal vents. These findings establish that metabolite-derived C:N ratios at hydrothermal vent communities are comparable to those at the chlorophyll maximum, displaying how chemosynthetic and photosynthetic communities produce similar biological signals despite their extremely different nutrient sources.