have not been included in this frequency distribution because of their 

 anomalous stratigraphy (Figure 3-37a and b) . At these two stations, 

 the surface consisted of 3 to 4 cm of intermediate-reflectance 

 sediment overlying a high reflectance layer 5 to 8 cm thick. Because 

 it is not possible to determine if the surface layer consisted of 

 oxidized or reduced sediment relative to the underlying unit, RPD and 

 OSI values could not be assigned to these two stations. However, 

 these two stations may have very low OSI values if the surface 

 sediment was sulphidic. The 5 to 8 cm thick high reflectance unit, 

 in turn, covered a low reflectance unit of unknown thickness which 

 extended below the limit of penetration of the optical prism. Station 

 200NW showed horizontal fractures in this low reflectance unit (Figure 

 3-37b) . This deformation was caused by brittle fracture of the 

 sediment as it was sheared by the descending optical prism. Such 

 brittle fracture takes place in fine-grained sediments when the water 

 content is less than 50%. Low water content is typical of 

 overconsolidated sediment. Although the stratigraphy at stations 200W 

 and 200NW had not been observed in previous surveys, a layer of 

 cohesive dredged material may occupy this quadrant of the disposal 

 area. The above interpretation is supported by diver observations 

 made on August 13, 1985: "The substrate consisted of fine silt (1 to 



2 cm deep) over a cohesive clay base Eroded clay clump material 



was present" (SAIC, 1989a) . 



The two distributional modes (Figure 3-38) described above 

 appear to have been spatially separated according to station location 

 (Figure 3-39) . Values less than 3 cm deep were located at stations 

 400W and 600W. Shallow values were also located in the SE quadrant 

 (200E, 200SE, 400S, and 600S) . The RPD values measured in this survey 

 were not significantly different from those measured in August 1985 

 (p = 0.38, Mann-Whitney U-test) . However, in a direct one-to-one 

 comparison, 4 stations appeared to have much shallower RPD values than 

 measured in August 1985: 400W, 200E, 200SE, and 600S. The shallower 

 RPD values at these stations may be related to the lingering effects 

 of Hurricane Gloria, which caused surface erosion at this mound. 

 Post-storm RPD values are available for station CTR, 200 meter 

 stations, and 600E (Figure 3-39) . 



Most stations (10 out of 17 or 59%) were in a Stage I 

 successional sere (Figure 3-40) . Five of these stations have not 

 progressed beyond this sere since August 1985 (CTR, 200W, 400W, 200NW, 

 and 200SW) . Five stations apparently experienced retrograde 

 succession since August 1985 (200N, 400N, 600N, 600S, and 600E) , while 

 only one station (200NE) apparently changed in successional status (I 

 to I-III) since August 1985. These apparent changes in successional 

 status must be interpreted with caution. In August 1985, three 

 replicates were taken at each station; these data showed that within- 

 station patchiness was high with respect to successional status. The 

 present survey was based on analysis of only one replicate per 

 station, so the issue of within-station variance of benthic community 

 structure cannot be addressed. 



16 



