Fine sand (median diameter 0.111 millimeter) was dumped into the 

 second enclosure in May 1973. After 1 day, the new bottom was still 15 

 centimeters above the old; by the third day almost all of the introduced 

 sediment had been scoured out of the enclosure and the original bottom 

 was exposed. The scouring was probably the result of rough seas and use 

 of finer sediment than that of the first experiment. Five days after 

 burial, five cores (15 by 15 centimeters) were taken from the second 

 experimental area, and one from the nearby unburied control area. 



Both experiments were concerned with the immediate effects of heavy 

 sedimentation or burial on the benthic fauna. The introduced sand layer 

 in the first enclosure remained intact for the 3-week observation period; 

 the fauna in the second enclosure was buried only 2 days. Since the 

 experimental conditions were not the same, each enclosure is discussed 

 separately. 



The first enclosure was observed 24 hours after the initial burial. 

 A large specimen of Callianassa sp. (ghost shrimp) and one Solen siaarius 

 (razor clam) were found on the surface of the introduced sediment. In 

 addition, the tube-dwelling polychaete, N. elegans , had burrowed through 

 the coarse sand and constructed new tubes from it. Nothria elegans was 

 one of the few animals whose abundance was not decreased by burial (Table 

 1) ; it is also a dominant large polychaete (S to 15 centimeters long) in 

 water depths from 10 to 30 meters on the open coast of central and south- 

 em California (Barnard, 1963) . 



Specimens of the gaper, Tresus nuttallii , had extended siphon holes 

 to the surface of the introduced sediment, similar to those described for 

 the mahogany quahog, Aratiaa istandioa , after burial by 9 to 17 centimeters 

 of sediment (Hale, 1972). Neither the gapers nor the quahogs had moved up- 

 ward. Sailia, Pratt, and Polgar (1972) concluded that slow sedimentation 

 would probably not endanger mahogany quahogs. 



The first enclosure data are presented in Table 9, and were compared 

 to samples taken from undisturbed control areas in July and August 1972. 

 All of the small crustaceans and mollusks were killed by burial. They 

 were found dead at the old bottom surface. 



Compared with the control, 66 percent of the worm species and about 

 50 percent of the individuals were killed by burial (Table 9) . Polychaetes 

 were the dominant group of worms . There were more nematodes in the exper- 

 imental area than in the control area. All of the animals that survived 

 the burial are commonly found in lower sediment strata. 



There are several animals characteristic of lower strata. Two poly- 

 chaete worms, N. elegans and Magelona spp., are active at the sediment 

 surface, live in vertical burrows, and withdraw deep into the sediment 

 when disturbed. Consequently, they were often recorded in lower strata; 

 however, their reactions to burial are different. Nothria elegans ad- 

 justed to the accumulation of sediment but the magelonids suffered a 90- 

 percent mortality. 



40 



