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A theoretical relationship between disturbance (and/or organic enrichment) and 

 Species numbers, Abundance, and Biomass (SAB) is shown in Figure 4-1 as modified from 

 Pearson and Rosenberg (1978). These relationships can form some basis for comparison of 

 mound successional dynamics compared to systems evaluated on their response to organic 

 loading. It should be noted that some systems show variations in their SAB response, and 

 the concept is best-developed in relatively enclosed estuarine systems (Maurer et al. 1993). 



The distribution of species abundance (richness, in units of number of species 

 per 0.04 m 2 ) and numbers of individuals (number of individuals per 0.04 m 3 ) show that the 

 thin apron deposits had the highest faunal densities and number of species (Figure 4-2). The 

 mound apex had the lowest species richness and abundance, and the mound plateau stations 

 were intermediate with respect to these parameters (Figure 4-2). The shape of these curves 

 suggests that the overall disposal mound was close to the Pearson and Rosenberg transition 

 (or ecotonal) part of the disturbance gradient (Figure 4-1). Because biomass was not 

 quantified in the traditional benthic sample work-up, this variable cannot be mapped. 

 However, qualitative inspection of the faunal collection indicates that biomass was greatest 

 at Station 300SE because of the presence of three genera of relatively large bivalves. In 

 Figure 4-1, note that biomass peaks in the Transition area (TR), and a subordinate biomass 

 peak exists under the Peak of Opportunists (PO). 



Although the species abundance and numbers of individuals increased away from the 

 center of the mound, calculations of diversity did not show such a clear trend. Diversity 

 indices are weighted to consider the impact of dominance by one or more species. The most 

 widely used diversity index is the Shannon-Wiener information statistic H' which is often 

 calculated with the statistic for Evenness, J'. The trends of these two statistics against station 

 type showed a complex relationship (Figure 4-3) until the effect of dominant species was 

 evaluated. Relatively low abundance; few species and high evenness (i.e., a small number of 

 species with similar abundance) characterized the CTR station. The resultant diversity was 

 low but in the same range as many other stations on the mound plateau and apron. Stations 

 75E and 150N both contained several dominant species that depressed the evenness and 

 diversity. Plotting the abundance to species ratio (Maurer et al. 1993) and examining the 

 effects of removing the top three dominant species (Figure 4-4), one can see this relationship 

 more clearly. The increasing abundance of individuals away from the center stayed ahead of 

 the increase in species, but peaked at Stations 75E and 150N, due to the influence of the top 

 three numerical dominant species (Figure 4-4). When the top three numerical dominants 

 were removed, the relative abundance to species decreased with distance from the center. 

 The relatively small sample size and influence of a few species on diversity indices limits the 

 conclusions that can be made about mound disturbance and community structure from these 

 data alone. However, it is clear that there were only marginal differences in diversity and 

 evenness apart from the station dominated by Nucula annulata (150N). 



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



