Recolonization was different in Zone 3 (low intertidal). The recolonization community developed 

 under the cages differently from the one that occurred when predators and grazers were not excluded. The 

 most common sequence of events is illustrated in Fig. 1 7g. 



In Zone 3, Mylilus edulis set in early summer, even if barnacles already occupied available substrata. 

 Mussels gradually out-competed barnacles (and all other organisms) for space, and by autumn, typically 

 occupied 100% of the caged substratum. The mussels persisted as long as the cages remained in place. 

 The cages were removed when crowding prevented further community development. Mussels were lost 

 within 2-3 days, either washed away as a mass, or heavily preyed upon by Urosalpinx. 



Alternatively, recolonization in Zone 3 could resemble that seen in Zone 2, i.e., development of a 

 Fucus canopy over a barnacle understory (Fig. 17h). These exclusion cage studies did not continue long 

 enough to determine the ultimate development of the low intertidal community. However, recolonization 

 transect studies discussed earlier show that re-establishment of a Chondrus population usually takes more 

 than 3-5 years. Exceptions occur and stochastic processes cannot be ignored. In one instance (specifically, 

 site 3 at White Point after the autumn denuding), Chondrus appeared in the cage area within 4 months, 

 and within a year, exceeded 85% cover. By contrast, Chondrus settlement never exceeded 5% in any of 

 the other experimental denudings. Obviously, recolonization is subject to natural variability. 



One important result of the exclusion cage studies is the conclusion that recolonization at Fox 

 Island-Fxposed was not affected by proximity to the MNPS discharge; the patterns of development seen 

 at FF were similar to those at other stations. The series of exclusion cage experiments was completed 

 before the shore community was altered following the opening of the second quarry cut. These data will 

 be particularly useful for assessing potential effects of 3-unit operation. 



The exclusion cage studies also show that grazers and predators exert their influence on local intertidal 

 communities, especially in mid and low intertidal areas, by preventing monopolization of space by a single 

 species (cf Menge 1975; Menge 1978). Grazers and predators help to maintain local communities in a 

 state of dynamic equilibrium, a balance between recruitment and growth, and senescence and removal. 

 This balance has persisted throughout the MNPS area during 2-unit operation. Where the community 

 balance has been disturbed (i.e., at FE following the opening of the second quarry cut), the community 

 responds to the changes as an entirety, and also in terms of its constituent species populations. 



49 



