65 



and 20 in Portland Harbor and several stations in the middle and upper 

 Bay. Reasons for these low densities are not completely obvious. 

 Stations with similar sediments located around stations 47, 49 and 50 

 have much higher densities. Further data are needed before we can 

 speculate on whether this is a natural or pollution-induced phenomenon. 

 Stations 18, 19 and 20 exhibited the highest levels of trace metals, so 

 perhaps the reduced densities there are impact related. The middle and 

 upper Bay stations with low animal densities are those where extremely 

 soft sediments were encountered. We believe that these sediments offer 

 so little bearing strength that only a depauperate community can 

 develop. 



Correlation analysis was used to add insight into factors that 

 might be influencing density levels. Density is correlated with both 

 depth and mean grain size (Fig. 20 and 21). These relationships, both 

 of which are significant at the 99%, level indicate that density 

 increases with increasing depth and decreases with decreasing mean grain 

 size. The latter relationship adds support to the hypothesis that 

 physical properties at some fine-grained stations prevent the 

 development of a normal community. Density is not significantly 

 correlated with temperature, salinity or organic carbon content. 



Correlation analyses were also run between density and the six 

 trace metals. Two of the metals, chromium and nickel, were negatively 

 correlated to density at over the 95% level. While not attaining the 

 conventionally accepted 95% level of significance, it is interesting to 

 note that cadmium, zinc, copper and lead are all negatively correlated 

 with density. The significance levels are 94, 93, 88 and 76%, 

 respectively. 



