36 THE OYSTER AND THE OYSTER INDUSTRY. 



amount of food organisms and material ascertained microscopically. " 

 Estimate is usually made per liter, which is about equal to a quart. 

 If it were found from a series of examinations that the food content 

 of the water were conspicuously low, it is obvious that the grounds 

 in question would not be desirable for the planting of oysters. 



Bottom. — ^The bottom is cleaned of debris by dredging. If firm 

 enough to support the oysters, no further preparation is needed. If 

 soft, the surface is hardened by putting down shells, sand, or gravel, 

 deposited uniformly so that there are no holes in the surface as finally 

 prepared. 



Sowing the seed. — The seed oysters are removed from the original 

 bed by the use of tongs or dredges and are planted in much the same 

 manner as shells by being shoveled from boats or scows (PL V, fig. 2) 

 towed back and forth over the grounds. About 500 bushels per acre 

 are usually planted, though the amounts vary widely with local con- 

 ditions. The oysters are spread uniformly, so that they may not lie 

 in heaps and cause some to fail to receive the proper amount of food 

 or to be crowded and thus grow irregularly. 



Care of beds. — ^The beds are generally left untouched after planting, 

 except for combating enemies in some cases (see below) and shifting 

 certain of the oysters, if desired, to other grounds for final prepara- 

 tion for market. The oysters to be shifted or sold directly are taken 

 up by the use of tongs and dredges. After the oysters have been 

 removed from the beds the grounds are cleaned up by dredging, 

 when they may be used again for planting cultch or seed. 



PROTECTION AGAINST ENEMIES. 



The more important enemies of the oyster will be described briefly 

 and the methods, if any, of combating each set forth. 



STARFISH. 



There are two species of starfish which may be classed as oyster 

 enemies. These are the common star, Asterias forhesi, and the 

 purple star, Asterias vulgaris. The starfish opens an oyster by inclos- 

 ing it with the arms or rays (PI. VI, fig. 1), which are provided with 

 rows of suckerlike feet on the lower side, and exerting a constant 

 outward pull on the valves of the shell, until the oyster is exhausted 

 and the valves are allowed to gape at the ends. The starfish then 

 protrudes its stomach from the mouth, which is on the lower side of 

 the central disk, inserts it between the valves of the oyster shell, and 

 sucks in and digests the meat. The set and 1 and 2 year old oysters 

 are more subject to the inroads of the starfish, because of their 

 smaller size and weaker adductor muscle; but the larger starfish 

 prey on oysters as much as 3 years old. 



In certain waters the starfish are very destructive to oysters, often 

 invading and cleaning out a whole bed before the planter is aware 

 of their presence. This is true of New England waters and those 

 immediately to the southward. They are unknown in Chesapeake 

 Bay and constitute a menace to oysters only in the regions mentioned 

 in the preceding sentence. In Narragansett Bay and Long Island 

 Sound it has been necessary to fight them very vigorously. 



a This method will suffice to determine the great bulk of the food available in the water and is usually 

 sufficient for practical purposes. The material in actual solution in the water, which probably contributes 

 only a small percentage of the food of the oyster, can be determined only by chemical analysis. 



