Extensive mineral deposition at vent sites in the northeast 

 Pacific has created a habitat where vent organisms live in close 

 intimacy with the processes of deposit formation (Fig. 1). This 

 area is an ideal natural laboratory for observation and 

 experimental study of the interaction of life processes with the 

 formation of mineral deposits. In this paper we describe three 

 on-going investigations of biological influences on mineral 

 deposition. Our approach has been one of combining in situ 

 observation and sampling with electron microscopic and 

 mineralogical analyses of preserved specimens. The major aim has 

 been to identify and describe organism-mineral interactions and 

 to develop hypotheses for future experimental and quantitative 

 investigations . 



VESTIMENTIFERAN TUBES: SURFACE AND STRUCTURAL EFFECTS 



The most common, and often largest animal found at vents is 

 the tube-worm; these are the famous gutless Vestimentif era with 

 symbiotic bacteria. After frequently observing vestimentif eran 

 tubes partially or completely incorporated into hydrothermal 

 mineral deposits (Fig. 2; also see Koski et al . 1984), we are 

 investigating mechanisms by which tubes are first encrusted by 

 minerals and then eventually entombed in growing deposits. The 

 central question is whether the tubes locally enhance mineral 

 deposition or whether they are simply being engulfed by processes 

 upon which they have little effect. In the laboratory the 

 microenvironment of the worm tube surface is investigated by 

 electron microscopy combined with energy dispersive x-ray 

 analysis. Structural effects such as alteration of vent fluid- 

 seawater mixing, leading to enhancement of mineral deposition 

 within tube worm aggregations are studied in situ with a time- 

 lapse camera, by monitoring growth of chimneys associated with 

 Vestimentif era . 



Processes At The Tube Surface 



Samples for electron microscopy of tube surfaces were 

 collected from vents on the southern Juan de Fuca site (Fig. 1) 

 (U.S. Geological Survey Juan de Fuca Study Group 1986). Some of 

 the most striking examples of mineral encrustation on tube 

 surfaces and chimney growth around tubes can be found at this 

 site (Fig. 3a). So called "clear" tubes from a vent where little 

 mineral deposition or encrustation was occurring (Fig. 3b) were 

 compared with samples from vents where occupied tubes were 

 frequently encrusted from the base to near the tube opening. 

 Examination of "clear" tubes with little encrustation revealed a 

 diverse bacterial flora colonizing the tube surface (Fig. 4a). 

 The most abundant members of this flora were sheathed bacteria 

 which frequently had accumulated minute Fe particles in the 



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