continental shelf and slope, which include the gutless clam, 

 Solemya johnsoni Dall, and the vestimentif eran, Lamellibrachia 

 barhami Webb, (Fig. 2). Lamellibrachia occurs at the deeper 

 vents at the base of the continental slope. Specimens of Solemya 

 johnsoni have been frequently collected along the continental 

 slope, as well as just seaward of the shallow-water chimney site 

 (Carey, unpublished data; Fig. 1). Calyptogena pacifica Dall 

 1891, also found at vent sites, has been collected from the upper 

 slope. Solemya clams are associated with active vents in deeper 

 waters and with sulfide-rich sediments ( Cavanaugh 1985; Suess et 

 al. 1985), and are present at the active vents found on the lower 

 slope (Kulm et al . 1986; Suess et al . 1985). Solemya sp. also 

 occurs in great abundance to the exclusion of other animals along 

 fault zones where fluids are being expelled (Suess et al. 1985). 

 Such fault zones are common within the accretionary complex on 

 the continental margin; Solemya may be associated with these 

 faults in many localities along the margin. 



Similarities between the Oregon lower slope methane-derived 

 CaCO^. chimneys and slabs and underlying geological structure 

 strongly suggest that the same geological and geochemical proces- 

 ses also operate in shallow water ( Schroeder et al . 1987). Vent 

 fluids from the lower Oregon subduction zone contain high 

 concentrations of methane, suggesting that shallow vent effluents 

 would also expel methane (Kulm et al. 1986; Ritger et al . 1987). 



Our integrated research program on the northern Oregon 

 continental margin proposed to determine if active subduction- 

 driven vents were present. Furthermore, we planned to define the 

 geology, biology, and geo-biological interactions in subduction- 

 driven vent fields of the upper accretionary complex. Dives with 

 the DSV Mermaid-II in 1987 and DSV Delta in 1988 showed that the 

 vent field we examined is extinct. However, active venting of 

 methane-rich fluids did occur in the area and formed abundant 

 CaCO,. slabs and chimney edifices. This paper documents the 

 effects of these formations on the nature of the local benthic 

 fauna. 



METHODS 



During August 1987, we utilized the DSV Mermaid-II to survey 

 the chimney field on Nehalem Bank (Fig. 1). In September 1988 we 

 undertook dives with DSV Delta for additional, more detailed 

 searches on and around Nehalem Bank off northern Oregon. During 

 many of the 1988 DSV Delta dives, the PHOTOSEA camera system, 

 loaded with 200 ASA Ektachrome film, took still photographs every 

 30 seconds. A hand-held video camera was used for continuous 

 recording of portions of the dives. 



Photographs (n - AAA) from 8 DSV Delta 1988 dives were 

 analyzed for distribution of invertebrate fauna and fishes by 



139 



