randomly dispersed. Subtidal clams were few and occurred at a maximum 

 density of 0.4 clams per square meter (95 percent C.L. = 0.465) at 

 Moss Landing. 



III. SEDIMENT STUDIES 



1. Introduction . 



There are no previous studies that relate sediment parameters to 

 distribution patterns of Pismo clams, but a few studies exist for other 

 species of bivalves. Maurer (1969) reported that the distribution and 

 abundance of most species of bivalves at Tomales Bay in western 

 California are strongly influenced by sediment type. Dunhill and Ellis 

 (1969) suggested sediment type may play an important role in regulating 

 the distribution of Maooma along Victoria, British Columbia. Pratt and 

 Campbell (1956) found the growth of the quahog Meroenaria mevoenaria was 

 curbed in sediments with a high silt-clay content. Swan (1952) observed 

 that the growth of the clam, Mya avencccia, may be strongly affected by the 

 type of substrate. The clams grew about twice as fast in sand as in a 

 compact mud -gravel -she 11 mixture. Sediment parameters play a strong 

 regulatory influence on the distribution and abundance of certain clams. 

 In this study, certain sediment parameters were correlated with the 

 presence and abundance of Pismo clams. 



2. Methods and Materials . 



Five sediment cores were taken at each site from 1- square-meter 

 quadrats which were randomly selected within the 60- by 80-foot grid 

 system. Cores 3.5 centimeters in diameter were taken with a plastic 

 corer, 56 centimeters long. Sediments were analyzed by the Emery tube 

 method (Emery, 1938) because it is a better measurement of the "hydraulic" 

 size value for particles of unusual shape, density, or porosity (Folk, 

 1966) . Since beach and intertidal sediments are under the influence of 

 the marine environment, sediment parameters are best described by 

 hydraulic properties. Sediments were analyzed for mean grain size, 

 sorting, skewness, and kurtosis, using equations by Folk and Ward (1957). 



Beach profiles were obtained for some beaches by sighting the horizon 

 (Emery, 1961). 



3. Results . 



Sediment parameters were analyzed to determine if there was a relation 

 of sediment type to the distribution of Pismo clams. Because clams, 

 particularly juveniles, are not found deep in the sand, only the top 

 2 inches of the sediment cores were analyzed. 



An analysis was made to determine if there was a difference in the 

 mean grain size of sand between beaches with and without clams. Because 

 the kurtosis estimates were not within the limits of a normal distribution 



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