About 1.5 years after disposal, the number of individuals was still 

 60 percent lower than before disposal. This reduction was as great as 

 that immediately after the disposal (Fig. 15) . The number of species and 

 species diversity and evenness were considerably higher (Fig. 14) . There 

 was little change in biomass because of the large terebellid, A. 

 oaaidentalis . These results were different from those reported by 

 Pfitzenmeyer (1970) who studied the recovery of a disposal site in an 

 estuarine environment. He concluded that after 1.5 years the same species 

 reestablished in the disposal area, and biomass and species diversity were 

 similar to predisposal levels. The general pattern of recovery in the 

 present study was similar to that observed by Sailia, Pratt, and Polgar 

 (1972). 



Paine (1966) and Dayton (1971) described the effect of biological and 

 physical disturbances increasing diversity in rocky intertidal communities 

 after clearing space occupied by the competitive dominant. Dayton and 

 Hessler (1972) discussed the role of disturbance in maintaining high div- 

 ersity in the deep sea. In contrast, Deevey (1969) reviewed the negative 

 correlation between disturbance and evenness; in southern California, 

 Peterson (1972) experimentally disturbed bivalve assemblages and reduced 

 evenness . 



No general trend exists between disturbance and species diversity or 

 its components. Sampling over a large disposal area, Sailia, Pratt, and 

 Polgar (1972) reached the same conclusion in relation to disturbance of 

 the bottom by dredged material dumping. In the present study, dredged 

 material disturbance reduced the numerical dominants (and possibly com- 

 petitive dominants); species richness and evenness increased during re- 

 covery. The bottom consisted of fine sand. Although turbidity is generally 

 high, strong tidal currents flush the channel several times a day, keep- 

 ing the bottom free of fine sediments and stagnant water. Current veloc- 

 ities often exceed 100 centimeters per second. The average water tempera- 

 ture was 13° Celsius (range, 9° to 17° Celsius, and salinity varied from 

 31.5 to 33.8 parts per thousand with a mean of 33.4 parts per thousand) 

 (Broenkow and Smith, 1972). 



In July 1971, two samples of eight replicates each were taken from the 

 harbor station before dredging; the fauna at the control and dredge sta- 

 tions were similar. Individual species (three capitellid polychaetes and 

 one oligochaete) (Table 5) were dominant. The dominant polychaete was 

 Notomastus tenuis, which was also dominant in the mudflats of lower Elk- 

 horn Slough and in the north harbor. The oligochaete occurred in the 

 highest numbers, but represented less than 5 percent the biomass of 

 N. tenuis. 



Two species of large bivalves dominated the biomass. The bent-nosed 

 clam, Maooma nasuta, which is, an active suspension and deposit feeder, 

 was more numerous than the large suspension-feeding gaper clam, Tvesus 

 nuttaltii. Both animals live in the lower intertidal mudflats to water 

 depths of a least 40 meters. Because the gaper was uncommon, essentially 

 sedentary, and lived deep in the sediment, it probably had little direct 

 effect on community structure. 



49 



