oxygen tension, water content, and retention of organic material. For 

 example, Weiser (1960) examined a bay environment and found few fauna in 

 common where silt-clay fractions differed. Sanders (1958, 1960) found 

 that grain size correlated with infaunal densities and was important in 

 determining basic feeding modes (suspension versus deposit feeding) of 

 the species. Closely related species may show distinct sediment-size 

 preferences (Clark and Haderlie, 1963). Nichols (1970) found that 

 polychaete species assemblages corresponded most clearly with clay 

 content. Mineralogical composition may be important to certain species 

 (Fager, 1964). In comparison with subtidal habitats, sand beaches 

 experience unique conditions (exposure to air, desiccation, and evapora- 

 tion) and greater vicissitudes of physical factors, and pose a more 

 restrictive habitat for macrofaunal organisms. 



Tidal height and exposure conditions are important factors. Their 

 relationships to physical and chemical factors which affect infaunal 

 distributions have been discussed by Bruce (1928), Newcombe (1935), 

 Emery and Foster (1948), Hedgepeth (1957), Johnson (1965), and Cox 

 (1976). 



In southern California, exposed beaches typically undergo sand 

 accretion in the summer (reduced wave energy) and erosion in the winter 

 (high energy); thus, sandbars build offshore in the winter and migrate 

 shoreward onto the beaches in the summer. Observations (unpublished) 

 support those of Speidel (1975) who reported that seasonal shifting of 

 sediment generally occurs in water less than 9.2 meters deep off south- 

 ern California and is greatest in the surf zone. Seasonal differences 

 in sand level may exceed 1 meter at a depth of 4.9 meters below mean 

 lower low water (MLLW) (personal communication, D. Aubrey, Scripps 

 Institution of Oceanography, 1977) . 



Sediment stability is an important factor in determining species 

 associations. Ansell, et al. (1972) found that species composition, 

 abundance, and zonation patterns were correlated significantly with 

 monsoon conditions and stability of substrate. Yancey and Welch (1968) 

 mentioned the heavy mortality of nearshore populations of Atlantic coast 

 surf clams during storms, though the impact upon population dynamics was 

 unknown. Enright (1962) documented the adverse effects of increased 

 wave activity upon a beach amphipod population. What is not known is 

 the extent of onshore-offshore migration of motile infaunal species in 

 response to such perturbations. Certainly apropos is Longhurst's (1964) 

 statement that the problem in studying these biological communities lies 

 in the lack of a simple starting point such as a landscape. 



Few studies have examined subtidal communities along exposed 

 coasts in depths of less than 7.6 meters. The biological community at 

 these shallow depths is continually affected by wave action. Day, 



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