Species Diversity 



Species diversity for each station was calculated using the Shannon information index: 



where n i = number of individuals of the i species, N = total number of individuals for all species and 

 S = number of species. An evenness component of diversity was calculated as: 



./ = ^^ {Pielou 1977) 

 "max 



where II max ='"8 S and represents the theoretical maximum diversity when all species are equally 

 abundant. Evenness ranges from zero to one and increases as the numbers of individuals among species 

 become more evenly distributed. Diversity calculations excluded oligochaetes and rhynchocoels (groups 

 that sometimes accounted for over 80% of the totals organisms collected) because they were not identified 

 to species. Similarly, other organisms that could not be identified to species, either because they were 

 juveniles or in poor physical condition, were excluded from this analysis. 



Numerical Classification and Cluster Analyses 



Cluster analyses, based on annual abundances of organisms were performed using the Bray-Curtis 

 similarity coefficient. This coefficient is calculated as: 



li^tj + ^ik) 



Sji^ = -%; {Clifford and Stevenson 1975) 



where X |j = abundance of attribute i at entity j and X jk = abundance of attribute i at entity k. Based 

 on these similarities, cluster analyses incorporating a flexible sorting strategy (B = -0.25) was used to form 

 station groups (lance and Williams 1967). 



