73 



center of the mound also was apparent in density calculations, ranging from 1.25 x 10 3 

 individuals/m 2 at CTR to 2.75 x 10 4 individuals/m 2 at 300SE. 



Polychaetes, with 12 species belonging to nine different families, constituted the 

 largest taxonomic group among the top ten dominant species from each station (Appendix 

 D; Tables 2, 3, 4). The second largest groups were bivalves (four species), with Nucula 

 annulata extremely abundant, and amphipods (genus Ampelisca). Two gastropod taxa, one 

 decapod, and one oligochaeta spp. complete the list of the dominant taxa (Williams and 

 Blake 1997). 



The most dominant species was the bivalve Nucula annulata, which was among the 

 top ten dominants at all six stations. The polychaetes Mediomastus ambiseta and Prionospio 

 steenstrupi were among the most abundant species at all stations, ranking with the top three 

 species at four stations. The polychaete Tharyx acutus and the gastropod genus Crepidula 

 were represented among the top ten dominants at four and five stations, respectively. 



Species diversity, as calculated by the Shannon-Wiener index H' (Section 2.0, 

 Methods), ranged from a low of 2.65 at Station 150N to 4.10 and 3.91 at Stations 150W and 

 300WSW, respectively (Table 3-3). The low diversity value at Station 150N was attributed 

 to the dominant presence of Nucula annulata. These Stage II deposit feeders physically stir 

 up the surficial sediment thereby decreasing the availability of suitable benthic habitat for 

 colonization by other species (Section 4). The diversity at Station CTR was relatively high 

 considering the low abundance of individuals. The high diversity relative to low species 

 abundance is indicative of an early stage of succession (Pearson and Rosenberg 1978). The 

 Shannon-Wiener index J', calculated for species evenness (Section 2.0, Methods), ranged 

 from 0.48 at Station 150N to 0.82 at Station CTR (Table 3-3). 



Rarefaction curves, showing the relative effect of species density and diversity, were 

 developed for the Seawolf samples (Figure 3-22, see Section 4.2.2.3 for discussion of 

 rarefaction curves). Samples collected at the center and 75 m from the center had relatively 

 lower species abundances and lower to moderate diversity values. The stations 150 and 300 

 m away from the center had two to three times as many taxa as the two more central 

 stations. Stations 150N and 300SE had lower to moderate diversity values; lower evenness 

 values, and therefore followed a similar rarefaction curve. Station 75E had similar diversity 

 and evenness values as 150N and 300SE, but the low species abundance depressed the 

 rarefaction curve. The westerly stations had the highest diversity values, with moderately 

 high evenness, and therefore were aligned along a similar rarefaction curve (Table 3-3 and 

 Figure 3-22). The implication of the abundance and diversity information relative to the 

 REMOTS® results is discussed in Section 4. 



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



