16 THE OYSTER AND THE OYSTER INDUSTRY. 



In this connection a distinction must be drawn between beds used 

 for seed production and those employed in growing and fattening 

 stock for the market. Oysters will frequently »row more rapidly 

 in silt-laden waters, on muddy bottoms, or in their vicinity, than 

 they will elsewhere, as such places are usually more productive of 

 food organisms, owing to the larger amount of dissolved material 

 available for the sustenance of the minute plants which constitute 

 a considerable part of the food of the oyster. 



Even adult oysters may be destroyed, however, by heavy deposits 

 of silt such as often result from freshets and crevasses. For the 

 purposes of seed culture or the establishment of self-perpetuatmg 

 beds the most desirable waters are those which contain an abundance 

 of microscopic vegetation with a minimum of suspended morganic 

 particles, although an organic slime such as rapidly forms on sub- 

 merged surfaces in some locahties is as effective in preventing the 

 fixation of spat as is inorganic sediment. In many places m Chesa- 

 peake Bay and in the bays on the New Jersey coast the sediment, 

 as weU as the bottom mud, is largely composed of finely comminuted 

 fragments of seaweeds and other vegetable matter the rapid deposit 

 of which soon covers with a flocculent fihn the surfaces of all objects 

 exposed to it, excepting when the currents are sufficiently strong to 

 exert a scouring influence. During warm weather this organic 

 deposit is likely to undergo rapid decomposition, the toxic products 

 of which sicken and kiU the oysters. 



The more or less constant dribbling of fine material upon the 

 bottom has comparatively little effect upon adult oysters, operating 

 mainly to cover the shells and prevent the attachment of spat or to 

 stifle the young oysters after attachment. This rain of fine material 

 occurs almost everywhere but especially where the currents are weak, 

 and it is generally m the latter localities that it is of sufficient volume 

 to be obnoxious. 



TIDES AND CURRENTS. 



The effects of tides and currents upon the development and growth 

 of oysters are quite important. The genital products, cast directly 

 into the water as previously stated, are moved about so that more 

 opportunity is afforded for the contact of the spermatozoa of the 

 male with the eggs of the female. 



The free-swimming larvaB are carried to and fro by the tides and 

 currents, and thus when large enough to set are often some distance 

 from where they were spawned. The importance of this fact in the 

 method of oyster culture by planting cultch is very great and the 

 matter is discussed under a separate section on page 31. 



Tides and currents tend to prevent the fouling of material upon 

 which the larvae set by washing away silt and debris. In still water, 

 as in an inclosed bay, the suspended debris has an opportunity to 

 settle upon the cultch and form a slime and film which prevents the 

 attachment of the larvae. If the larvse have attached, the deposit 

 is often sufficient to smother them. 



Since the food of oysters consists of microscopic materials found 

 in the water (see p. 19), it follows that currents affect the distribu- 

 tion of the food of the oyster. In still water, nearly all the organ- 

 isms might settle to the bottom or those in the neighborhood of the 



