Spatial relationships within and among stations may be illustrated 

 by representing percent standardized Bray-Curtis similarity coefficients 

 as a clustering dendrogram. Figure 2 depicts the data from the 

 undisturbed transects in the 1983 reporting period, analyzed by station 

 and zone; three groups (and one outlier) are apparent at the 50% level. 

 The high degree of similarity within these groups, and the very low 

 similarity among them illustrate the three distinct zones in the local 

 intertidal community. The inclusion of FEl and FS3 into a cluster 

 otherwise made up of Zone I J stations is caused by the high proportion 

 of Fucus in the high intertidal at Fox Island-Exposed, and the low 

 abundance of Chondrus in the low intertidal at Fox Island-Sheltered. 

 The low degree of similarity between SS3 and any other site is 

 attributed to an increase in mussels, to the detriment of Chondrus; as 

 theorized previously, if the same phenomenon occurs at Seaside Exposed, 

 this type of analysis should quickly detect it. Since 1979, this 

 technique has consistently identified the three designated shore zones 

 (and their variations) . These analyses indicate that the criteria used 

 originally to define the zones were biologically valid, and also that 

 few changes to the structure of intertidal communities in the Millstone 

 Point area have occurred from 1979 to present. 



Although major changes to the intertidal community from year to 

 year have not been detected, the same analysis technique can be used to 

 illustrate variability within years (e.g., seasonality). When the data 

 for each collection since April 1979 are analyzed (Fig. 3), three 

 seasonal groupings are apparent: A) spring/early summer (April and May), 

 characterized by high abundance of Monostroma pulchrum , Ulothrix f lacca , 

 and Bangia atropurpurea , B) late summer/autumn (July-October, and in 

 mild years, December), when Poly s iphonia harveyi , Ulva lactuca , and 

 Chaetomorpha linum are most common, and C) winter (December-February), 

 when epiphytism is lower and ephemeral algae are rarer. The subdivision 

 of Cluster B is probably due to the recovery of Fucus populations at 

 most stations over the past two years. 



In summary, the intertidal community, as represented by the 

 undisturbed transects, may be interpreted as a balance between 

 recruitment and growth, and senescence and removal. This balance is 

 subject to variability induced by inter- and intraspecif ic competition 



16 



