314 



ECOLOGICAL FACTORS: 



first significant numbers of red algae (Rhodophyta). 

 Among the red algae are various coral-like and 

 feather-like forms. In addition, animals are more 

 numerous and more varied. 



Zone IV usually displays the greatest diversity and 

 numbers of plants and animals. The more con- 

 spicuous algae are laminarians, a group of brown 

 algae diagnosed by their long, straplike blades. 



SUCCESSION 



Although the details of the process of transition 

 through various unstable communities to a stable 

 community, or climax, at a particular place is to be 

 delayed, some consideration of the phenomenon is 

 of help here. 



Intertidal areas are not stable. They can be 

 transformed, owing to deposition, to fresh-water sites 

 or to land (Figure 17.8). (See Figure 4.17 and related 



discussion, pp 54-55. In the transformation to fresh- 

 water sites the first step is the development of quiet 

 waters and a salt marsh, a situation already preva- 

 lent in quiet marine waters. The transformation from 

 saline marsh could be directly to a land habitat, but 

 in the change to a fresh-water area, it involves sedi- 

 mentation leading to greater elevation of the bottom 

 to a point where marine waters no longer invade the 

 area. Further steps to a land habitat might be in- 

 ferred from the discussion of fresh-water succession 

 (pp. 318-322). 



Intertidal succession to land might be assumed to 

 start with the Zone IV condition and, again as a re- 

 sult of sedimentation, the site proceed to Zone I. 

 From Zone I, further development probably approxi- 

 mates normal land succession from bare rock, a sub- 

 ject to be delayed until the general topic of suc- 

 cession (Chapter 19). However, in sandy areas near 

 the ocean (strands) certain unique stages might be 



c 

 o 



o 

 o 



Figure 17.8 Plant succession near the ocean; possible sequences from marine to terrestrial habitats. 



