294 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



shells are gradually dissolved in tlie sea water, aud thus furnish the lime -which the 

 growing oyster needs to build up its own shell. As long as the shell is soft and thin 

 the danger from enemies is very great, and this danger is greatly diminished as 

 soon as the shell becomes thick enough to resist attack. It is, therefore, very neces- 

 sary that the vshell should be built up as rapidly as x>ossible, and an abundant supply 

 of food in general will be of no advantage unless the supply of lime is great enough 

 for the growth of the shell to keep pace with the growth of the body. All sea 

 water contains lime in solution, but the percentage is, of course, greatest near the 

 sources of supply. It is well known that on coral reefs, which are entirely made of 

 lime, all kinds of shelled mollusks flourish in unusual abundance and have very 

 strong and massive shells, and our common land and fresh-water snails are much 

 larger and more abundant in a limestone region than in one where the supply of 

 lime is scanty. In such regions it is not unusual to find the snails gathered around 

 old decaying bones, to a\ hich they have been drawn in order to obtain a supply of 

 lime for their shells. 



From all these causes combined it results that a young oyster which settles upon a 

 natural oyster-bed has a much Itctter chance of survival than one which settles 

 anywhere else, and a natural bed thus tends to perpetuate itself and to persist as a 

 definite, well-defined area; but there is still another reason. As the flood tide rushes 

 up the channels it stirs up the fine mud which has been deposited in the deep water. 

 The mud is swept vip onto the shallows along the shore, and if these are level much of 

 the sediment settles there. If, however, the flat is covered by groups of oysters, the 

 ebbing tide does not flow oft" in an even sheet, but is broken up into thousands 

 of small channels, through which the sediment flows down to be swept out to sea. 



The oyster-bed thus tends to keep itself clean, and for these various reasons it 

 follows that the more firmly t'stablished an oyster bed is the better is its chance of 

 perpetuation, since the young spat finds more favorable conditions where there are 

 oysters, or at least shells, already than it finds anywhere else. 



Now, what is the practical importance of this description of a natural bed ? It is 

 this: Since a natural bed tends to remain permanent, because of the presence of 

 oyster shells, the shelling of bottoms whore there are no oysters furnishes us with a 

 means of establishing new beds or of increasing the area of the old ones. 



The oyster-dredgers state, with perfect truth, that by breaking up the crowded 

 clusters of oysters and by scattering the shells the use of the dredge tends to enlarge 

 the oyster-beds. The sketch which we have just given shows the truth of this claim, 

 but this is a very rough and crude way of accomplishing this end.* 



This description, so far as it relates to tlie oysters themselves, gives 

 a good idea of tlie average oyster-bed, though they differ somewhat in 

 details in different localities. But, as shown in the sections which treat 

 of the enemies and the food of the oyster, the latter is very far from 

 constituting the entire population of the beds. Tlie same causes which 

 induce the growth of the oyster, the firm basis of attachment, the sur- 

 rounding food-producing mud, the favorable density and temperature, 

 all tend to make the oyster-bed a center teeming with aquatic life. 

 Thus a single point of attachment, a firm nucleus projecting naturally 

 above the surrounding mud, or a few shells thrown upon the muddy 

 bottom may give rise to a community where life is as abundant and the 

 struggle for existence as complex and strenuous as is anywhere found 

 in nature. 



Brooks, W. K., Maryland Oyster Report, 1884, pp. 86 to 88, inclusive. 



