l^C-acetate (10 yCi; 50 mCi mmol" , New England Nuclear, Cat. 

 #NEC-553) were added individually to one of the four bottles at 

 each temperature. The samples were incubated for 18 hours at 

 which time the particulate materials were collected onto Whatman 

 glass fiber filters (GF/F) and stored frozen until analyzed for 

 incorporation into total acid insoluble material (Karl 1982). 



Enrichment culture experiments 



Eight different elective culture media (Table 2) were used 

 in an attempt to characterize the physiological groups of 

 bacteria at Pele's Vent. Dilution-to-extinction procedures were 

 employed to determine the relative numerical importance of each 

 group. Two water samples from Pisces V dive #29 and scrapings 

 from a rock recovered from the active vent field were serially 

 diluted with sterile artificial seawater, inoculated into the 

 various media and incubated at 22°C under the conditions 

 indicated (Table 2). 



RESULTS AND DISCUSSION 



General Appearance of Pele's Vent Field: First Impressions 



Pele's Vents are situated in the southwest portion of the 

 summit of Loihi Seamount at a water depth of 980 m. The area of 

 active hydrothermal fluid discharge is restricted to the flank of 

 a relatively small volcanic cone approximately 10-15 m below the 

 summit elevation. The active field is less than 0.5 km^ and is 

 characterized by numerous individual vents discharging waters 

 heated to a temperature of at least 30°C. The vent orifices are 

 distinguished by a white precipitate (Fig. 2a) which has been 

 determined to contain high concentrations of elemental sulfur 

 (G. McMurtry, pers. comm.). The sulfur deposition is most 

 likely the result of bacterial oxidation of reduced sulfur 

 species contained in the discharged waters. The vent fluid is 

 exceptionally clear and nearly devoid of suspended particulate 

 matter. 



At least four potential habitats exist for the growth of 

 hydrothermal vent bacteria. The first is the subsurface vent 

 system itself which is technically difficult to sample except by 

 obtaining discharged hydrothermal fluids. It should be kept in 

 mind that the chemical composition of this suspected growth 

 habitat is unknown but is likely to differ substantially from the 

 fluids collected at the points of discharge where rapid mixing 

 with ambient bottom water is known to occur. Likewise, the 

 bacteria sampled from the hydrothermal vent fluids may not be 

 truly representative of the assemblages growing in the 

 interstices of the volcanic edifice. The second habitat is the 

 region immediately surrounding the vent loci where the 

 presumably anoxic hydrothermal fluids are mixed with oxygenated 



198 



