Short-term changes and cause and effect relationships were the most 

 difficult to detect. Seasonal changes were distinct. Similar seasonal 

 phenomena were also observed at the shallower stations. Reproductive 

 cycles, recruitment processes, and natural mortality explain the general 

 trends. Adverse physical conditions increased mortality and restricted 

 recruitment during winter months. Winter recruitment was probably more 

 successful in deeper water, where wave action had less effect on substrate 

 stability. Thus, physical and biological conditions were both important 

 in determining the observed seasonal variations. 



Long-term changes were also observed. The most noteworthy was the 

 successful recruitment and persistence of A. occidentalis from June 1972. 

 Another factor that caused long-term irregular variations in the fauna was 

 yearly changes in climatic conditions. These irregular changes favor the 

 successful recruitment of different species at different times. Milder 

 conditions during the first year caused less mortality and spring recruit- 

 ment was high. 



Significant correlations between dominant species and number of indi- 

 viduals indicated that dominants were of major importance in determining 

 the variations. However, at the same time significant correlations be- 

 tween the number of species and individuals indicated a general increase 

 in mortality and recruitment of all species. 



The decrease in the number of species with decreasing depth and in the 

 number of species and individuals during winter months suggests that these 

 assemblages are primarily physically controlled (Saunders, 1968). 



2. Experimental Burial of the Benthic Fauna . 



The 20-meter control station was located on a relatively stable, flat 

 bottom (Fig. 1). The benthic population at this station consisted of 

 small epifauna and shallow infauna. To test the effect of burial under 

 controlled conditions, bottom areas were experimentally buried on two 

 occasions near the 20-meter control station (Fig. 1). 



Two open-ended sheet metal frames 1.5 by 1.5 by 1 meter high were 

 pushed 0.5 meter into the sediment. Each enclosed a 2.25-square meter 

 bottom area. Sediment, which was devoid of animals, was dumped into the 

 framed areas until a 15-centimeter layer covered the old substrate. The 

 first frame was positioned on 26 August 1972; the second on 3 May 1973. 



Coarse beach sand (median diameter 0.32 millimeter) was placed in the 

 first enclosure in August 1972. Six small cores (7.5-centimeter diameter, 

 30-centimeter height) were taken at various times from the experimental 

 area during the 2 weeks following burial, and one large core (15 by 30 

 centimeters) at the end of 3 weeks (Table 9). The cores were partitioned 

 at the interface of the old and new sediment and processed. 



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