Primary production in marine ecosystems is through photosynthesis in the euphotic zone and chemosynthesis in the deeper zones. Hydrothermal systems can be powerful primary production sites, usually dominated by chemolithoautotrophic prokaryotes. The plume from a hydrothermal vent contains many potential sources of metabolic energy, e.g. hydrogen, methane, sulfur compounds, and iron. The primary production in the plume occurs mainly in the early stage of plume evolution, and then gradually spreads into the surrounding ecosystem. The planktonic community of hydrothermal vent fields can use some of the organic matter in the plume, and could play a role in connecting the chemosynthesis-based and photosynthesis-based food chains. The stable isotope ratios of nitrogen and carbon were analyzed with respect to the depth, site, and organism type to characterize the trophic structure of the planktonic communities at hydrothermal vent fields. We will discuss trends seen in the trophic structure of communities and consider the influence played by the surrounding environmental, geochemical and microbial conditions.