Strong wave action and bottom surge directly affect deposition 

 and erosion of nearshore sediments. Movements of nearshore sand can 

 strongly influence the size of sand dollar populations. Merrill and 

 Hobson (1970) reported that D. excentvicus is occasionally carried by 

 sliding sediments to depths of 37 meters. Shifting substrates and sedi- 

 ment composition affect sand dollar populations. Weihe and Gray (1968) 

 found that the sand dollar, Mellita quinquiesperforata, a genus related 

 to DendrasteT, was adversely affected by a high percentage of silt and 

 mud. In the laboratory, Mellita had a definite preference for sandy 

 substrate. Dredging, which deposited heavy amounts of silt and mud near 

 their study area, totally eliminated sand dollar populations, which had 

 been abundant in previous years. Turbidity and silt deposition affected 

 settling of Mellita larvae or smothered juveniles which had settled. 

 Along the California coast large populations of D. exaentriaus existed 

 in areas preceding dredging operations (MacGinitie, 1935, 1939; Ricketts 

 and Calvin, 1952), but have not been found since (Merrill and Hobson, 

 1970). Burial of D. exaentriaus is not the crucial problem since they 

 may undergo natural burial when conditions become unfavorable. However, 

 under buried conditions water circulation and food supply must be main- 

 tained. Fine sediment loads may prevent this. Merrill and Hobson 

 (1970) and Weihe and Gray (1968) found the optimum habitat for sand 

 dollars to be clean, well-sorted sand with moderate water currents. 



Core sampling at 3.7- and 6.1-meter depths included a large 

 part of the typical B. exaentriaus depth range, and the individuals 

 collected varied widely in size (Fig. 30). Newly metamorphosized juve- 

 niles (<2 millimeter) were found at the 3.7-meter depth in all surveys 

 except survey V which occurred 5 months after the end of the beach 

 deposition program, and after the first winter storm. Survey IV (post- 

 dredge disposal) found juveniles at all 3.7-meter depth stations but 

 more abundant at station C than at the 3.7-meter impacted stations A and 



Divers found extensive beds of sand dollars at the 3.7-meter 

 depth only for stations A and B in surveys I and II (predisposal surveys) 

 At these stations during surveys III and IV, the sand dollars were 

 buried under 3 to 9 centimeters of fine sediment, but they appeared to 

 be alive and healthy. In survey V, none were observed at any of the 

 3.7-meter stations. Divers found no adult D. exaentriaus beds at 6.1- 

 meter depths in surveys I and II. During survey III (station B, 6.1 

 meters), scattered small individuals were found covered by 3 to 9 

 centimeters of fine sediment. This survey was concurrent with beach 

 replenishment; the highest percentage of the fine silt for the entire 

 study period was found on this survey. At station A, 6.1 meters, survey 

 IV, there were no adult specimens of D. exaentriaus observed, but at 

 station B, 6.1 meters, survey IV, they appeared common and were buried 

 by 3 to 9 centimeters of silt. At the latter station in survey V, the 

 individuals that were previously common, had moved out of the area, and 

 only a few scattered specimens remained. However, in survey V, abun- 

 dant beds were present at station A, 6.1 meters, survey V. Since 

 number and size of these individuals were similar with individuals 



85 



