SUPRALITTORAL ZONE <, 



LITTORAL ZONE< 



INFRALITTORAL ZONE < 



TREME HIGH WATER LEVEL 



EXTREME LOW WATER LEVEL 



SUPRA- 

 >LITTORAL 

 FRINGE 



MID- 



■TORAL 

 ZONE 



INFRALITTOR- 

 AL FRINGE 



FIG. 28-6 Diagram illustraf- 

 Ing terminology of lonation 

 on rocky coasts (Stephen- 

 son 1949). 



the species of larvae which will settle, but this needs 

 more study. Young periwinkles are transported by 

 wave action to the lower margin of stony beaches, 

 and further shoreward movement is mainly loco- 

 motive. They achieve their proper zonation by the 

 end of the first year of life (Smith and Newell 1955). 



Littoral zone 



Brown algae form thick masses and give pro- 

 tection to those animals that find shelter in or under 

 them. A fauna of copepods, ostracods, water mites 

 and young littorinids inhabit these seaweeds. In 

 England, the numbers of individuals per 100 g of 

 seaweed vary from about 44 on brown algae to 

 over 13,000 on lichens (Colman 1940). 



The animal life on rocky shores is varied and 

 luxuriant. Several species of acorn barnacles, snails, 

 marine limpets, marine mussels, goose barnacles, 

 sea anemones, chitons, sponges, hydroids, bryozoans, 

 flatworms, annelids, amphipods, isopods, crabs, sea 

 urchins, starfishes, tunicates, and insects are present. 

 Total abundance of animals may run into tens of 

 thousands of individuals per square meter (Allee 

 1923, Newcombe 1935, Dexter 1947, Yonge 1949, 

 Stephenson 1950, 1952, 1954, Shelford et al. 1935, 

 Hewatt 1937, Ricketts and Calvin 1948). 



Subliitoral zone 



This community is not subjected to exposure 

 by tides or to the pounding of surf, but is affected 



considerably by wave action and the complete circu- 

 lation of water. Animals move around somewhat 

 more freely and there is less need for strong holdfast 

 structures. Most organisms lack physiological toler- 

 ance for long exposure to the air and hence differ 

 fundamentally in structure and mores from the com- 

 munity described above. 



Laminarias or kelps are the largest of the brown 

 algae and occur commonly in this community. They 

 have root-like holdfasts attached to the bottom and 

 their stalks, which are often several meters long, 

 bear leaf-like branches that float at the surface in the 

 larger species. A long list of animals find shelter 

 and food in the kelp beds and especially in the pro- 

 tection of the holdfasts (Andrews 1945). Polychaete 

 worms are particularly abundant in these holdfasts 

 (Colman 1940). Filamentous red algae (Rhodophy- 

 ceae) are also prominent. 



Abundant characteristic animals on the Pacific 

 coast are sea urchins, sea cucumbers, starfishes, 

 snails, rock oyster, chitons, limpets, scallops, mussels, 

 nudibranchs, barnacles, crabs, hermit crabs, hydroids, 

 tunicates, shrimps, and various fish. Distribution of 

 fish species correlates strongly with the type of bot- 

 tom or benthos that is present (Popov 1931 ). 



The variety of animals in this community is great, 

 both in genera and species, but the density of any 

 one benthic species is seldom greater than 10/ni^ on 

 the Pacific coast of North America (Shelford ct al. 

 1935), in contrast with the littoral zone. Off the 

 coast of California, the average fresh weight of the 

 standing crop of plants decreases at depths of 1.5 to 

 22 m from 4667 to 606 g/m^, while animals increase 

 from 125 to 377 g/m- (Aleem 1956). 



Marine biomes 363 



