Figure 18. — Biologists examining a dredgeload of bottom material from an oyster bed invaded by starfish. 



Recently, chemical methods of control were 

 found efficient in some instances. For ex- 

 ample, to protect beds of soft clams, Mya 

 arenaria , in Maine, bait treated with chemi- 

 cals poisonous to crabs was found effective. 

 The bait usually consists of pieces of fish 

 treated with insecticides, such as Lindane. 

 Crabs eating this bait soon die. The chemical 

 method, however, should be used with great 

 caution because in certain areas, such as 

 Chesapeake Bay, the blue crab, C^. sapidus , 

 even though an oyster predator, constitutes an 

 important commercial fishery. In other areas, 

 such as waters of Maine, the bait may be 

 carried away and later eaten by lobsters, 

 killing them. It is believed, nevertheless, 

 that eventually poisonous baits of truly spe- 

 cific types will be developed so that they will 

 affect only the undesirable species. 



There is no doubt that several species of 

 fish also feed on oysters, especially young 

 ones. One variety, the so-called "black drum", 

 Pogonias cromis, travels in schools and is 

 known to destroy entire oyster beds in a 

 comparatively short time. This fish, which 

 attains a length of several feet and has large, 

 strong, crushing teeth, ranges from New 



Jersey to Texas. As long as 40 years ago 

 fences were used in shallow water to protect 

 oysters from invasion and destruction by 

 drums . 



Skates also feed on oysters and clams. 



Competitors 



There are several species of boring sponges 

 belonging to the genus Cliona which infest 

 shells of oysters. Although the boring sponge 

 is not a true parasite, because it merely 

 excavates tunnels in the calcareous shells of 

 oysters to provide itself a shelter, the boring 

 sponges kill many oysters. 



Probably the most common boring sponge is 

 C. celata, which normally begins its existence 

 in summer when it settles, after a free- 

 swimming larval period, on shells of oysters 

 and bores a small tunnel through the shell. 

 Eventually the shell is honeycombed, and the 

 sponge tunnels may penetrate the shell com- 

 pletely (fig. 19). Shells of old oysters severely 

 riddled by sponges are extremely brittle. The 

 sponge may spread over the outside of the 

 shell and smother the oyster. 



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