in maintaining the physical structure of the intertidal community, a 

 loss or reduction of any of these species would have a dramatic effect 

 on the appearance and stability of the intertidal region. Should any of 

 them disappear, there are no other organisms that are capable of filling 

 those functional niches (Vadas et al. 1976; Price 1980) . 



Recolonization studies - The recolonization studies described 

 earlier were designed to determine the patterns and rates of recovery of 

 intertidal communities (particularly the species mentioned above) following 

 substratum denudation. Presumably, colonizing germling and juvenile 

 stages would be more susceptible to environmental impact, and therefore 

 could detect a more subtle alteration of conditions (Bird and McLachlan 

 1974). The denudings simulated the worst possible impact (i.e., total 

 removal of biota) ; hence, they represent a much more severe perturbation 

 than any expected power plant effect. Exclusion cage experiments were 

 included to assess the effect of grazing and predation on recolonization. 



In the Millstone area, Urosalpinx cinerea is the dominant predator; 

 Littorina spp . , especially _L. littorea , are the dominant grazers. 

 Predators and grazers can exert a profound influence on the structure of 

 the intertidal community (Southward 1964; Menge 1978; Peterson 1979), 

 although they are not dominant in terms of percent cover. In fact, the 

 relationships between the abundance of algae and sessile animals., and 

 the numbers and activity of the snails suggest that the latter have a 

 direct effect on the abundance of the former, in terms of percent coverage. 



Many intertidal organisms have life histories that include relatively 

 short reproductive periods at a specific time of year; therefore., the 

 initial stages of recolonization are dependent on the time of denuding. 

 For example, if substrata are cleared in early spring (March) , one of 



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