Authors used photogrammetric and videogrammetric data collected at 13 degree N/EPR by the French manned submersible Cyana during the Biocyatherm and Biocyarise cruises to estimate the biomass of vent fauna. Two distinct faunal assemblages are associated with low- and high-temperature vents, Vestimentifera. The former, characterized by giant tube worms and bivalves, the latter by the so-called "Pompeii worms" (Alvinellidae). The cold vent biomass may reach 8.5 kg m super(2), far in excess of the hot vent biomass which amounts to 2.4 kg. Such a difference is linked to higher integrated symbiosis between primary and secondary producers in cold vent assemblages, hot vent secondary production being dependent upon separate ingestion/digestion processes.