(2) Significant increase in total species present with 

 increased fine fraction (particles less than 0.125 

 millimeter median grain diameter]. 



(3) Significant increase in organic carbon with silt. 



These results indicate a possible effect of silt and fine sediment 

 fractions on the diversity and abundance of benthic infauna in the 

 subtidal zone; this positive correlation suggests that silty sediments 

 which are being washed offshore may temporarily enrich the nearshore 

 biota on the way to equilibrium conditions at greater depths. Fine 

 sediments did not remain long on the beach (e.g., station A, Figs. 

 8 and 9) after deposition. The increased carbon with added silt may 

 have an adjunctive effect. Although carbon did not directly show 

 significant correlation with abundance and diversity, it showed a 

 positive correlation (p<.05) with silt. 



Particle size generally decreased with depth. This is a function 

 of the wave energy impinging on the bottom affecting sorting and trans- 

 port processes. Certainly, typical increases in diversity with depth 

 (Sanders, 1968; Gray, 1974; Parr and Diener, 1978) correlated with 

 increases of fine sediments offshore may reflect the covariance of these 

 factors with important energy-related factors (e.g., orbital velocity on 

 the bottom) . Water motion on the bottom may be very important to in- 

 faunal organisms. The disposal of appreciable amounts of silts in the 

 nearshore environment by the beach replenishment provided an opportunity 

 to assess the importance cf silts as a single factor within different 

 wave energy zones and its significance was noted. 



3. Major Species . 



This section discusses the biology and effects of beach nourishment 

 upon major or "key" species. In this report "key" species refer to 

 species that were numerically abundant or contributed greatly to the 

 biomass or are believed to be important in structuring the composition 

 of the nearshore community. 



a. Bendvaster exaentrious (Sand Dollar) . Dendraster has a major 

 role in determining dynamics of shallow- sand communities along the 

 coast. Bendvaster is capable of forming extensive beds and is probably 

 the most significant biomass component in shallow water just beyond the 

 surf along its geographic range from British Columbia to central Baja 

 California. At Imperial Beach, there was a greater number of infaunal 

 species in areas with Bendvaster compared to similar areas and depths 

 without Bendraster. This may be due to creation of greater habitat 

 complexity by Bendvaster (Table 21). 



83 



