reds 



□ browns 



ireens 



Fig. 3. Relative species proportions of major algal divisions under pre-operational and 3-unit operation (March 

 1986-February 1987) conditions. Numbers in bars represent percentage of total flora; height of bars represents numbers 

 of species in each division. 



Undisturbed Transects 



Zonation is a universal feature of rocky intcrtidal 

 communities (Stephenson and Stephenson 1949, 

 1972; Lewis 1964). Local rocky intertidal com- 

 munities are separated into horizontal bands rep- 

 resenting the high, mid, and low intertidal zones, 

 where the high intertidal (Zone 1) consists mostly 

 of bare rock and barnacles {Balantis balanoides), 

 the mid intertidal (Zone 2) is dominated by a 

 canopy of the perennial brown alga Fucus 

 vesiculosus over an understory of barnacles, and 

 the low intertidal (Zone 3) is dominated by the 

 perennial red alga Chondnts crispus. Although 

 zonation appears stable on a localized scale, it is 

 subject to natural influences such as degree of 

 exposure, desiccation, temperature, storms, ice- 

 scour, predation, and competition, as well as man- 

 induced influences, which can alter the abundance 



of intertidal populations and increase the com- 

 plexity of the conununity. 



Similarity Dendrogram 



To discern pattern in this complexity, the Bray- 

 Curtis similarity index has been utilized to char- 

 acterize the community at each station in terms 

 of average annual abundance of each mid and 

 low intertidal taxon (measured as percentage of 

 coverage on permanently marked, undisturbed 

 transects, sampled six times per year). The sim- 

 ilarity index was calculated for each station/year 

 combination, and a clustering Jilgorithm was ap- 

 plied to the resultant similarity matrix. Exami- 

 nation of the hierarchial dendrogram (Fig. 4) al- 

 lows generation of hypotheses concerning the re- 

 lationships among stations and among years. 

 First, the general patterns of similarity among 

 stations and years (including 1986 data, marked 

 with asterisks in Fig. 4) were identical to those 



22 



