120 



peak of opportunists (PO, in Figure 4-1). This is another reason for fitting Seawolf Mound 

 data into the ecotonal part of the disturbance gradient. 



Biomass data were not available from the traditional grab sampling data taken to 

 document S and A. However, Station 300SE had a significantly higher biomass than the other 

 stations related to the presence of several large bivalve specimens. This observation suggests 

 that Station 300SE was farther to the right of the ecotonal point than other Seawolf stations 

 and therefore had experienced less intensive and/or less frequent impact than other stations. 



The results are consistent with the predictions based on the topographic location of 

 the stations and sediment type. The CTR station experienced the greatest disturbance due to 

 massive physical disturbance, and/or ecological impacts of the presence of a layer of gray 

 plastic glacial clay from new work dredging that has low food value and is resistant to 

 penetration by infaunal organisms. The broad area of the mound plateau was variable in 

 levels of disturbance and successional response, but generally represents an expected pattern 

 of recovery 1-2 years after a mound is capped. The station located on the apron (300SE) 

 showed the lowest level of disturbance to the extent that large, long-lived bivalves were still 

 in place and the successional stage was transitional (Stage II). 



4.2.2.4 Evaluation of Recolonization in 1998 



Because the 1998 survey was conducted nearly two-and-a-half years after completion 

 of disposal, the recolonization paradigm predicts that the successional stage in 1998 will be 

 dominated by Stage HI organisms (Germano et al. 1994). The monitoring results confirmed 

 this prediction, but there was some evidence of a continuing effect of the gray clay. The 

 results of the 1998 survey indicated that the successional status of the Seawolf Mound was 

 advanced, showing healthy Stage n, Stage II to m, or Stage II on IE communities inhabiting 

 the sediments (Table 3-1). The large chaetopterus tubes on the sediment surface also 

 provided evidence of stable, recolonized dredged material. Overall, the average OSI values 

 were less than those observed in 1997, primarily due to shallower mean RPDs measured in 

 1998. At the reference areas, the mean RPDs were slightly greater in 1998 at the NLON 

 REF and WEST REF reference areas, and lower at NE REF than observed in 1997. 



At the Seawolf Mound, the lowest mean RPDs in 1998 were observed at two stations 

 on the southwestern side of the central mound area (Figure 3-18). Although in general, the 

 lower RPDs tended to be over the central area, the RPDs were variable spatially. The 

 calculated average RPD suggested that the depth of the oxidized layer had become shallower 

 since the 1997 survey. However, this apparent reduction was due primarily to five stations 

 sampled in 1997 that had RPDs of >4 cm (Figure 4-5). In both 1997 and 1998, the modal 

 RPD was 1-2 cm, which was slightly less than the modal reference RPD (2-3 cm). This 

 result indicates that the majority of measured RPDs were similar from one year to the next. 



Monitoring Cruise at the New London Disposal Site, Seawolf Mound 1995 - 1998 



