composed entirely of recolonization collections, after the barnacle set 

 in spring of 1982, but without much other community development. As at 

 Fox Island-Exposed, Cluster D represents the three collections made 

 immediately after denudation; they show low similarity to any other 

 combination of collections but, since ephemeral algal cover is slight, 

 considerable similarity among themselves. 



Recovery to pre-experimental conditions is slower after an autumn 

 denuding than nfter a spring denuding. There is a delay until the 

 following spring for recolonization of barnacles (and F ucus at exposed 

 stations) into strips denuded in autumn. However, the same conclusion 

 based on data from the spring denuding holds; i.e., rate and degree of 

 recovery of the intcrtidal community are directly related to degree of 

 exposure, and inversely related to intertidal height. The experiments 

 to determine the effect that time of year in which denuding occurs has 

 on recolonization will be discussed in much more detail in next year's 

 report, after the entire seasonal cycle of denudlngs and exclusion cage 

 studies is completed in Apri] 198A. 



Exclusion Cages and Controls 



The importance of grazing and predatinn to the development of the 

 intertidal community has been discussed in previous sections, and in 

 other reports (Hughes 1980). Snails in particular (especially Littorina 

 littorea and Urosalpinx cinerea ) exert a profound influence on the 

 spatial and temporal distribution of algae and sessile invertebrates 

 (NUSCo 1983). A series of exclusion cage studies has been in progress 

 since 1979, to determine the effect that grazers and predators have on 

 the development of recolonization communities. As in the recolonization 

 studies described above, we wished to determine if the rates and 

 patterns of recolonization were dependent on the time of year in which 

 denuding occurs. Previous experiments began in April 1979, June 1980, 

 and September 1981; each ran for 15 months. The present experiment 

 represents a winter denuding, and was begun in December 1982. This 

 study is not yet complete; as mentioned above, a thorough treatment of 

 seasonality as it applies to recolonization will be included in next 

 year's annual report. 



22 



