Species diversity = H" = E -— log — — 

 1=1 



S = total number of species 



rij^ = the proportion of the i species 



N = total number of individuals 



^max ~ natural log of S. 



Evenness = J = H'7H^^^ 



The most important environmental parameters along the control transect 

 are related to wave action. Grain size increases and substrate consolida- 

 tion decreases with increasing wave action. Movement or resuspension of 

 sediment is undoubtedly the most significant ecological factor. Sediment 

 stability effects species composition and abundance. 



The 6-meter station was located near the edge of a large bed of the 

 common sand dollar, Dendraster exaentrious. The bed moved inshore and 

 offshore in response to wave action. Adult sand dollars were present at 

 the shallow station during certain times of the year; juvenile sand dol- 

 lars (1 millimeter) occurred sporadically in relatively large numbers at 

 the two deeper stations. 



There was a distinct change in sediment stability between the 10- 

 and 20-meter depth and a consequent change in the fauna. The composition 

 of deep sediment strata changed; substrate consolidation and the vertical 

 distribution of the infauna increased (Oliver, 1973). The number of per- 

 manent tube and burrow-dwelling animals and the commensals living in the 

 burrows and tubes of other animals (e.g., pinnotherid crabs and scale 

 worms) increased with increasing water depth. The permanent tube and 

 burrow inhabitants included many polychaetes and Calliccnassa. In addi- 

 tion, a number of large bivalves that live deep in the sediment were also 

 present at the 20-meter station. The gaper clam (Tvesus) was the most 

 conspicuous. Maximum density was reached in 30 meters of water; only a 

 few individuals were found in water shallower than 15 meters. Tresus is 

 a sedentary suspension feeder which is intolerant of scouring, deposition, 

 and resuspension of coarse sediment in shallow water. 



The crustaceans were dominant at the two shallow stations (Table 8) . 

 These were mostly small amphipods and ostracods that are motile and bur- 

 row in the top few centimeters of sediment. At the 20-meter station, the 

 worm fauna dominated; this trend also continued into deeper water (Oliver, 

 1973). 



Most of the mollusks were juveniles of the bivalve, T. modesta (1 mil- 

 limeter). A number of other species of juvenile bivalves were present as 

 transient, sporadic members of the assemblages and suffered high mortality 



33 



