96 Our Food Mollusks 



plenishes the supply. Up to a certain point, the more 

 rapid the current, the greater will be the amount of 

 available food. But one current bears more food than 

 another. Salt water, for example, that flows out from 

 shallow marshes during the ebb tide, usually bears great 

 numbers of diatoms because the marshes are warmer 

 than the sea water outside, and the higher temperature 

 stimulates a rapid multiplication of these organisms. 

 Food is sometimes so abundant that a rapid current is 

 not necessary. For this reason it is not possible to give 

 a rate that shall be most favorable for oyster growth 

 in all localities. 



The presence of suspended silt in the water is a con- 

 dition to be observed with care. It is an especially im- 

 portant problem in the Gulf of Mexico. There it is 

 found that oysters often thrive and reproduce in local- 

 ities where, much of the time, the water is very muddy. 

 But it is also true that currents in such places are too 

 rapid to deposit much of their silt. In more quiet 

 waters, where mud slowly collects on the bottom, ma- 

 ture oysters may be able to exist, but even a slight deposi- 

 tion is fatal to newly attached spat. Finally, there are 

 many places where mud collects so rapidly that life on 

 the bottom is impossible. Much experience is needed to 

 enable one to recognize these conditions, when searching 

 for available bottoms not already occupied by oysters. 



Oysters will grow in water having a summer tem- 

 perature so low as to prevent reproduction. At several 

 points on the coasts of Washington and California, small 

 Atlantic seed oysters grow to marketable size. The 

 summer temperature is much lower than on the Atlantic 

 below Cape Cod, and the sexual products mature only in 

 certain warmer coves. Experiments made many years 



