Following the initial discovery of microorganisms and 

 macrofauna at the Galapagos Rift spreading center, similar mid- 

 ocean ridge hydrothermal vent communities were discovered along 

 the East Pacific Rise (at 10°57'N, 12°49'N, 20°50'N and 18°31'S), 

 the Juan de Fuca-Endeavor-Explorer Ridge system (at 46°N, 

 130°01'W; 46°53'N, 129°17'W; 45°57'N, 130°01'W; 47°57'N, 

 129°04'W; and 49°44'N 130°18'W) and the mid-Atlantic Ridge (at 

 26°N and 23°22'N). These so-called "hard lava" hydrothermal vent 

 systems have numerous shared geochemical characteristics 

 resulting from the circulation of seawater through mid-ocean 

 ridge crustal materials. However, they also vary considerably 

 with respect to the nature and extent of heat dissipation and in 

 the structure and organization of their associated animal 

 communities. 



In addition to the hydrothermal vents which have been 

 investigated at sediment-starved mid-ocean ridge spreading 

 centers, active hot springs have also been discovered at several 

 sediment-rich sites including the Guaymas Basin (a sediment 

 covered ridge axis; 27°02'N, 111°22'W), the Manus Basin (a back- 

 arc basin of the New Britain arc-trench system; 3°10'S, 

 150°17'E), the Okinawa Trough (a back-arc basin of the Ryukyu arc 

 system; 27°34'N, 127°09'E) and, most recently, at Loihi Seamount 

 (an active hot-spot volcano in the Hawaiian Archipelago; 18°55'N, 

 155°16'W). The existence of hot-spot hydrothermal fluid discharge 

 is significant in that deep-sea vents and associated biological 

 assemblages need not be restricted to oceanic plate boundaries. 

 This paper reports the results of our initial microbiological and 

 chemical investigations of samples collected from the summit of 

 Loihi Seamount. 



METHODS 



Habitat Description 



Loihi Seamount is a seismically active submarine volcano 

 that marks the southernmost extent of the Hawaiian island chain 

 and the probable site of an emerging Hawaiian island (Fig. 1). 

 It is one of the two known active hotspot submarine volcanoes of 

 the Pacific Ocean; the other is the Macdonald Seamount of the 

 Austral Island chain. Persistent swarms of earthquakes, 

 characteristic of those associated with Hawaiian volcanism, occur 

 near the summit of Loihi. 



Detailed photographic surveys and dredging operations at the 

 summit of Loihi initially provided evidence for the presence of 

 fresh, glass-encrusted pillow lava, talus, and pockets of sand 

 and gravel as well as several fields of hydrothermal iron oxides 

 and nontronite (Malahoff, McMurtry, Wiltshire, and Yeh 1982; 

 DeCarlo, McMurtry, and Yeh 1983). In 1983, Horibe, Kim and Craig 

 reported elevated concentrations of methane ( CH 4 ) and helium-3 in 

 the water column above Loihi indicating the presence of active 



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