328 Our Food Mollusks 



vored places, shallow boxes or racks, containing three or 

 four inches of sand, were suspended one above another, 

 and clams planted in them grew very rapidly, many gain- 

 ing an inch in length in five months. It was found pos- 

 sible to obtain good results in a strong current even 

 when young clams were placed close together in these 

 boxes. This " intensive farming " possesses many ob- 

 vious advantages. By selecting a locality in which a 

 strong current carries much food, a maximum growth 

 could be attained with large numbers of clams, for much 

 water above the bottom could be utilized. Such clams 

 could easily be examined, and a market demand for a 

 definite size could be met with little labor. On the other 

 hand, there might be practical difficulties in handling 

 continually submerged racks, and the expense of the 

 method might be prohibitive. But interesting results 

 might come of rack culture if it were practised on a com- 

 mercial scale, and it is worth an extensive trial in more 

 than one locality. 



The hard clam is apparently as little affected by dif- 

 ferences in the salinity of water as is Mya. It was found 

 to reproduce normally and to grow in waters in which 

 salinity varied from 1.009 to 1.025. The oyster is much 

 more sensitive to these variations. Outside much nar- 

 rower limits than these, its general condition, and espe- 

 cially its power of reproduction, are seriously affected. 



Natural enemies of the adult are few, and do little 

 damage. Starfish destroy some, and a few are killed by 

 one or two boring mollusks (Figure 64). Probably 

 there are heavy losses among the young before they are 

 able to burrow, but once in the bottom, they are secure. 



Sufficient preliminary biological work has been done 

 to make it certain that the quahaug industry, the newest 



