Burial o£ offshore organisms by fines transported from the beach 

 replenishment material could have a greater adverse impact than inter- 

 tidal burial. This is because offshore population densities are higher 

 and dominant species with high biomass (e.g., the sand dollar, Den- 

 draster exoentriaus) are long-lived; they successfully recruit to form 

 new beds only sporadically and modify the nearshore habitat (stabilize 

 sediments and enhance diversity). Burial of sand dollar beds at 

 Imperial Beach does not appear to have any induced significant immediate 

 mortality but questions of delayed mortality and recruitment success 

 require longer term studies. 



At the termination of the field study (November 1977), other than 

 changes in beach profiles and increased coarseness of the deposited 

 material, there appeared to be no other long- lasting measurable physical 

 changes at Imperial Beach due to beach replenishment. 



To minimize biological impacts of beach replenishment, dredged 

 sediments should closely match the composition of indigenous sediments 

 at the deposition site. This may conflict with other project objec- 

 tives, such as increasing sand coarseness to slow erosion or the avail- 

 ability of appropriate sediments for dredging. The percentage of fine 

 sediments (smaller than 125 micrometers) should be low to minimize 

 siltation and consequent anoxic sediment conditions offshore. 



The nearshore community at Imperial Beach is adapted to seasonal 

 transport of sediments. Consequently, the deposition of some sediments 

 on the beach is part of a natural cycle. The nearshore community 

 appears to be highly resilient to this type of perturbation; however, 

 offshore the biological community is more diverse and does not regularly 

 receive high sediment loads. Consequently, the organisms appear less 

 adapted to this type of perturbation and are less resilient. In con- 

 clusion, if clean sandy sediments are disposed of in the sandy nearshore 

 environment, deposition in the intertidal area probably has the least 

 biological impact. 



100 



