periods and were decreased by a storm just before the fifth survey, 5 

 months after deposition of beach sediments CFig- "^1- 



Biological activities of the sand dollar, V. excentriaus , may 

 have had an effect on infaunal communities within the subtidal zone. 

 They comprised a large part of the biomass and migrated on and offshore. 

 This movement possibly influenced other infaunal organisms; however, the 

 sampling program did not provide a detailed picture of D. exaentr-iaus 

 movements. A total of 14Q taxa was collected from the subtidal zone 

 (App. B) . This compares with the 131 taxa reported from the subtidal 

 (to 7.6-meter depth) at Imperial Beach by Dexter (1977). 



e. Faunal Similarities . Similarity indices at the 3.7- and 6.1- 

 meter stations were compared for the five surveys at station B. No 

 changes related to beach nourishment were detected (Table 13) . The 

 greatest changes observed appeared to be related to a storm which pre- 

 ceded survey V, 5 months after deposition. 



f. Biomass Relationships . Biomass data from all surveys are 

 presented in Table 16. An increase in the biomass proceeding offshore 

 is evident. The sand dollar, D. exoentriQus , accounted for 87 percent 

 of the total biomass at 3.7- and 6.1-meter depths. Biomass data were 

 too variable and sporadic in relation to T). exaentrious distribution 

 (Fig. 30) to be useful in assessing deposition effects. 



g. Abundance and Diversity in Relation to Depth . Relationships 

 are presented in Figure 31 and Tables 17 and 18. During the study 

 period there was a significant (p<.05) increase in abundance and species 

 density proceeding from the upper to middle strata of the intertidal 

 zone. At the lowest stratum of the intertidal zone there was a drop in 

 abundance (not significant at the p<.05 level) and species density was 

 similar compared to the middle stratum. Differences between the inter- 

 tidal zone and 3.7 meters were pronounced and significant (p<.05); 

 however, total abundance and species density did not increase much 

 between 3.7- and 6.1-meter depths. These relationships are in accord 

 with other observations of increased diversity in less physically con- 

 trolled (more stable) environments with increasing depths proceeding 

 offshore (Day, 1967; Sanders, 1969; Day, Field, and Montgomery, 1971; 

 Parr and Diener, 1978). Although they appear to be more stable and di- 

 verse, communities in deeper water may be more susceptible to changes in 

 physical variables since they do not regularly experience them. The 

 nearshore communities, although experiencing greater vicissitudes of 

 environment and fluctuations in abundance, may be a more resilient 

 system. Ecosystem resiliency is discussed in Holling (1973). 



h. Community Composition in Relation to Depth . Relative numbers 

 of species and abundances of major taxonomic groups change with depth 

 (Table 19) . The intertidal zone was dominated by crustaceans both in 



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