Wk -_;, 



Figure 13 Exposed rocks at East Point, Nahant, Mass. The 

 left side is toward the open ocean. The seaweeds Ascophyllum 

 (a) and Fucus (/) pinch out and are replaced by the barnacle 

 Balanus (&). (Courtesy Wisconsin Xat. Hist. Soc.) 



Figure 14 An abundance of the periwinkle Littorina littorea 

 and the barnacle Balanus on a rock when boulders are present, 

 Nahant, Mass. (Courtesy Wisconsin Nat. Hist. Soc.) 



