31 



fibers (the byssus) formed by the hardening of the secretions 

 from a ghmd in the foot, and they never change their position 

 after they have settled down from their free-swinnning stage. 

 Sometimes the mussels are so numerous that they fill up all the 

 spaces between the oystei-s and cover the entire outer surface 

 of all the shells. 



The mussels do no violent damage to the oysters; but since 

 the food of both fhese forms consists of the same kinds of 

 diatoms, it follows that the more mussels there are on a given 

 bed, the less food there will be for each of flie oysters, and the 

 less chance for the food materials being brought to the open 

 ends of the oyster shells, as the mussels have the first chance 

 at the Avater to strain out the food. 



TIYDROIDS. 



The presence of hydroids is detrimental to the oyster bed 

 in that they keep down the amount of food organisms that can 

 be available to the oyster, not as in the case with the mussels — 

 because they feed on the same plants, but because the hydj-oids 

 grow up above the ends of the oyster shells and form a sort of 

 a strainer which tends to keep back some of the food which 

 would otherwise reach the oysters. Besides cutting down the 

 food supply, the hydroids collect a great amount of sediment 

 from the water and thus tend to 'cover up fhe oysters and inter- 

 fere with their breathing as well as Avith their food supply. 



ALGAE. 



Several forms of marine plants, of the class known as algae 

 sometimes do considerable damage to the oyster beds, both by 

 keeping down the available food supply— so that the oysters do 

 not get fat: and because their presence on the shells of an 

 oyster has a detrimental effect on the market value. It is very 

 dififieult. or practically impossible, to clean off this growth so 

 that the oysters may be used for shell stock, while if they are 

 1o ])e used for canning, the presence of the alga gives the jneats 

 a disasrreealilo flavor when they have been steamed. 



BUCEPHAIvUS. 



The presence of Bnccphahis, a parasitic worm, has been re- 

 ])orted from the oyster beds of Louisiana on several occasions. 

 In the adult stage tliis worm is parasitiv^ in some of the fishes 



