Reproductive activity of the benthic organisms has two peak periods 

 correlated with the winter-spring and fall-winter seasons. Both seasons 

 are characterized by the rapidly changing length of days. Two peak phyto- 

 plankton blooms also coincide with the two periods of high reproductive 

 activity by the benthos that frequently have young that form part of the 

 zooplankton and feed upon phytoplankton. Many of the benthic animals are 

 sporadic spawners; some spawn in winter and others almost all year long. 

 Yearly changes in currents, water temperatures, and wave energy at critical 

 early life can affect the successful settlement of benthic animals and 

 cause the composition of benthic populations to differ yearly. 



Experimental burials were made at two enclosed areas on the stable 

 flat bottom at a water depth of 20 meters. One of the areas was covered 

 with coarse sand to a depth of 15 centimeters and sampled at various times 

 during the 2 weeks following burial. The other area was covered with fine 

 sand to the same depth but by the third day the covering had been scoured 

 away and the original bottom exposed. This area was sampled 2 and 5 days 

 after burial. 



The first enclosure had several tube-dwelling worms {Nothria) burrow 

 up through the coarse sand and construct tubes from it. Nothria was one 

 of the few animals whose abundance was not decreased by burial. Some 

 gaper clams extended their siphon holes to the new surface. All the small 

 crustaceans and mollusks were killed by burial; burial also killed 66 

 percent of the worm species and 50 percent of the individuals. All of the 

 animals that survived burial are commonly found deep in the bottom. 

 Nematode worms increased in the experimental area. 



The bottom of the second area was buried for only 2 days. About 69 

 percent of the species and 82 percent of the individual crustaceans and 

 mollusks were killed by the short burial. Worm mortalities were low. 



Disposal of the dredged material affected benthic animals in a less 

 stable substrate. Tliere was an 8-percent reduction in the number of 

 species and a 60-percent reduction in the number of individuals. 



Capability to withstand burial can be predicted by the animals' struc- 

 ture, behavior, usual vertical distribution in the bottom, and the sta- 

 bility of the substrate normally inhabited. 



One and one-half years after disposal, the number of individuals was 

 still 60 percent less than before disposal. However, the number of 

 species, species diversity, and evenness was higher than before. Biomass 

 was little changed although the species composition had changed. 



The immediate effect of dredging upon the channel area was to remove 

 the two species of large bivalves (the bent-nosed clam and the gaper clam) 

 that dominated the biomass. The bent-nosed clam was more numerous than 

 the larger gaper. Many oligochaete and polychaete worms were also removed. 

 The original population was a stable deposition-feeding assemblage. In 

 contrast, the recolonized area was completely different after dredging and 



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