plants and animals. This phenomenon is considered to be a universal feature of rocky shores (Stephenson 

 and Stephenson 1949, 1972; Lewis 1964). 



Locally, we recognize three intertidal zones; identified as the high, mid, and low intertidal. The high 

 intertidal (Zone I), primarily bare rock, is seasonally occupied by barnacles {Balanus balanoides) and 

 ephemeral algae (mostly Ulothrix flacca, Bangia atropurpurea, Blidingia minima, or blue-greens). Fucus 

 (mostly F. vesiculosus, occasionally F. spiralis) may occur in small amounts in the high intertidal. 



Barnacles and the fucoids Fucus vesiculosus and Ascophyllum nodosum dominate the mid intertidal 

 (Zone 2). Other algae in Zone 2 grow directly on rock (e.g., Ralfsia verrucosa, Enteromorpha spp.) or as 

 epiphytes of fucoids (e.g., Elachista fucicola, Polysiphonia spp.). 



The low intertidal (Zone 3) is typically dominated by Chondrus crispus, though fucoids may also be 

 common. Barnacles are seasonally abundant, but usually obscured by an algal canopy. Other algae may 

 be attached to rock (e.g., Ralfsia, Corallina officinalis, Dumontia contorta) or to larger algae. Monostroma 

 pulchrum and Polysiphonia spp. are common ephemeral epiphytes. 



The preceding description is not meant to imply that local intertidal communities are static or 

 homogenous; that is far from the case. Rather, the rocky shore is patchy, a mosaic of plants and animals 

 in dynamic equilibrium. Organisms compete for space, light, and nutrients. Processes of recruitment, 

 colonization, and growth are balanced against predation, senescence, and death. These processes vary over 

 space and time, on varying scales. 



General patterns of spatial and temporal distribution may be illustrated by plotting abundance (mea- 

 sured as percent substratum coverage) over time for the major components of the local intertidal commu- 

 nities (I'igs. 6-10); data for all taxa are included in Appendix RS lb. In each case, data are presented as: 

 a) a time-series beginning in March 1979, to show long-term trends and year-to-year variability, and b) 

 all years combined, calculating monthly means ± 2 SE, to show seasonal trends. For example. Figure 6 

 presents barnacle coverage in each zone, and abundance of predatory snails (mostly Urosalpinx cinerea 

 and Thais lapillus) in Zone 3. Generally, barnacle coverage is highest in the mid intertidal (Zone 2) and 

 higher at exposed stations (e.g., BP, FE) than at sheltered stations (e.g., SS, FS). There are differences 

 between years, but most variability occurs annually, i.e., a seasonal cycle. Barnacles settle in early spring. 



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