The significantly greater numbers of organisms settling on 

 thick-elevated than thin-elevated plates suggests that eddies at 

 the leading edges of thick plates enhance settlement. This trend 

 is also seen in the difference in settlement on the thick-elevated- 

 manganese and thin-elevated plates. Several different 

 interpretations, however, can be made of the low faunal densities 

 found on thick-benthic plates. One is that the benthic plates were 

 positioned lower in the boundary layer in slower oncoming flows, so 

 that the leading-edge eddies were consistently smaller than those 

 over elevated plates. If the size of the eddy influenced 

 settlement, then fewer larvae may have settled on the benthic 

 plates. On the other hand, settlement onto the thin plates was 

 greater than onto the benthic thick plate, and no leading-edge eddy 

 should have formed over the thin plate in flow conditions observed 

 at the study site. Thus, it is possible that the higher boundary 

 shear stress over elevated plates had more influence on settlement 

 than the presence/absence of an eddy. A third explanation, that 

 has nothing to do with settlement, is that the benthic plates were 

 grazed by predators unable to access the elevated plates. Mucus 

 trails found on one of the benthic plates (not used in this 

 analysis) lend some support to this explanation. 



Detailed spatial analyses of organisms attached to individual 

 plates will help resolve the difference between responses of larvae 

 to turbulence generated by a leading edge from responses to 

 downstream gradients in boundary shear stress (Mullineaux and 

 Butman, submitted). In addition, analyses of the species 

 composition of settled organisms will address questions on the 

 species-specific responses of deep-water larvae to f erromanganese- 

 encrusted substrates. 



ACKNOWLEDGMENTS 



This research was supported by contract N00014-87-K0007 from 

 the Office of Naval Research, a grant of submersible time from 

 NOAA, and the Coastal Research Center at Woods Hole Oceanographic 

 Institution. We thank the pilots and crew of the Pisces V 

 submersible for their technical assistance and enthusiasm. W. 

 Terry generously loaned the current meter and P. Boutin assisted 

 with the mooring design. This is contribution 6694 of the Woods 

 Hole Oceanographic Institution. 



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