30 



3.2.5 Successional Stages 



Stage II, Stage II on III, and Stage III taxa dominated the successional seres present in 

 the NL-TR survey area (Figure 3-17). Stage II, a transitional stage to Stage III, was 

 characterized by tubicolous amphipods which formed extensive tube mats on the sediment 

 surface. When these organisms were present with the deep-dwelling, head-down feeders in 

 Stage III, the successional stage was classified as Stage II on III. A typical Stage II on Stage 

 III assemblage was present at 300N while feeding voids originating with Stage III taxa were 

 readily apparent at 200SW (Figure 3-18). Stage III taxa were present in at least one of the 

 replicate photographs at 60% of the disposal site stations while a combination of the above 

 stages accounted for 76% of the disposal site stations. Stage III polychaetes are known to be 

 able to move upward through decimeters of sediment as observed at the Field Verification 

 Program (FVP) site in Long Island Sound (Germano and Rhoads 1984). It is likely that 

 colonization of fresh dredged material by adult Stage III organisms occurred as the adults 

 burrowed upward through the dredged material. The majority of stations with Stage I only 

 (small pioneering polychaetes) or Indeterminate (IND) designations occurred primarily on the 

 eastern half of the NL-TR survey area where active bedforms and/or fresh dredged material 

 were present. 



Reference areas NE-REF and NLON-REF were similar in successional status to the 

 NL-TR survey area; however, more of the reference area stations were at Stage II (Figure 3- 

 17). Stage II taxa were also present with Stage III organisms in replicate photographs at 

 many of the Stage III stations at NLON-REF. Much of the NLON-REF area was dominated 

 by torn tube mats of Stage II organisms. Ripped tube mats were also present at NE-REF 

 although less extensively; the majority of these tube mats were intact. Successional stages at 

 the WREF were largely indeterminate due to the scoured shell lag surface and shallow 

 camera prism penetration depth (Figure 3-8). At the few WREF stations with sufficient 

 penetration, Stage I only, Stage II only, and Stage III taxa were evident. 



3.2.6 Organism-Sediment Index (OSI) 



The multiparameter Organism-Sediment Index (OSI), used to characterize gradients in 

 habitat disturbance, could only be calculated at those stations where RPD and infaunal 

 successional stage were also determined. The OSI is determined on the basis of RPD depth, 

 infaunal successional stage, the presence or absence of methane, and presence of no/low 

 dissolved oxygen near the sediment surface as deduced from optical reflectance of the 

 sediment. The range of potential indices is -10 to +11. Based on results of past REMOTS® 

 surveys OSI values of +6 or less are considered indicative of chronically stressed benthic 

 habitats and/or those which have experienced recent disturbance (e.g., erosion, sediment 

 transport, dredged material disposal, hypoxia, intense demersal predator foraging, etc.; 

 Rhoads and Germano 1986). 



Monitoring Cruise at the New London Disposal Site, June 1991 



