26 



erosion, changes seafloor chemistry, or causes major reorganization of the resident 

 benthos. These perturbations can be natural events (i.e., strong currents or a passing 

 storm) or anthropogenic events (i.e., dredged material disposal or power plant effluent). 



Pioneering assemblages (Stage I) usually consist of dense aggregations of near- 

 surface living, tube-dwelling polychaetes. These organisms begin to populate a sediment 

 deposit within day^ of a benthic disturbance, as they readily exploit the competition free 

 space. Due to their limited interaction with the sediment, these organisms are usually 

 associated with a shallow RPD. 



In more stable environments Stage I assemblages are replaced by infaunal deposit 

 feeders or larger tube dwellers (Stage II). Typical Stage II organisms in Long Island 

 Sound include shallow-dwelling bivalves and tubicolous amphipods. In general, tubicolous 

 amphipods are common in eastern Long Island Sound. The presence of dense aggregations 

 of these amphipods (Ampelisca sp.) in the area surrounding NLDS has been identified as a 

 cyclical phenomenon as the spring-summer and over-winter populations mature, reproduce, 

 and decline. As a result, the timing of the individual REMOTS® surveys over the years 

 have documented the amphipod populations in eastern Long Island Sound during different 

 stages of the life cycle. 



Stage III biota represent a high-order successional stage and are usually associated 

 with areas of seafloor that is not usually subject to surface disturbances. Stage III 

 assemblages (infaunal invertebrates) are typically head-down deposit feeders whose feeding 

 behavior usually results in distinctive subsurface voids. The foraging activities of Stage III 

 organisms are capable of introducing oxygen-rich bottom water to the sediment at depths 

 approaching 10-20 cm below the sediment-water interface. As a result, the bioturbational 

 activity of Stage III organisms tends to cause the deepening of the RPD. 



A multi-parameter REMOTS® Organism-Sediment Index (OSI) has been 

 constructed to characterize habitat quality (Table 2-4). Habitat quality is defined relative 

 to two end-member standards. The lowest value is given to those sediments which have 

 low or no dissolved oxygen in the overlying bottom water, very shallow RPD depth, no 

 apparent macrofaunal life, and methane gas present in the sediment. The REMOTS® OSI 

 value for such a condition is minus 10 (-10). At the other end of the scaler an aerobic 

 bottom with a deep RPD, evidence of a mature macrofaunal assemblage, and no apparent 

 methane gas bubbles at depth will have a OSI value of plus 11 (+11). OSI values of +6 or 

 less are indicative of chronically stressed benthic habitats and/or those that have 

 experienced recent disturbance (i.e., erosion, sediment transport, dredged material 

 disposal, hypoxia, intense demersal predator foraging, etc.; Rhoads and Germano 1982). 



Monitoring Cruise at the New London Disposal Site, 1992 - 1998 



