32 OYSTER BOTTOMS OF MISSISSUPPI EAST OF BILOXI. 



was found off Deer Island, near Biloxi. Nowhere during the survey 

 was the salinity above or below that which oysters will tolerate, 

 although in Pascagoula River it sometimes fell below that at which 

 good marketable stock is ordinarily produced. In times of prolonged 

 and very heavy rainfall undoubtedly the water in Pascagoula River 

 becomes entirely or practically fresh, and the influence of its discharge 

 must be felt in a pronounced reduction of the salinity of the sound 

 near its mouth. 



OYSTER FOOD. 



In reports on previous surveys a feature usually has been made of 

 the subject of the quantity of oyster food carried by the waters. 

 These discussions have been confined, practically, to diatoms, minute 

 microscopic plants, which authors generally have been prone to 

 regard as supplying practically all of the oyster's nutriment. Volu- 

 metric studies of the micro-organism content of the water begun in 

 connection with the survey of Matagorda Bay * in 1905 revealed a 

 quantity so small as to excite the author's suspicion that the living 

 matter was of less relative importance than had been generally 

 supposed. 



It appeared possible, however, that the quantity of water filtered 

 by the oyster might be greater than generally supposed and digestion 

 more rapid; and that despite appearances the small quantity of 

 microscopic living organisms in the water and present in the stomach 

 at any one time might be sufficient material for the growth and gen- 

 eral physiological activities of a sluggish animal like the oyster. 



To test the matter, apparatus and methods ^ were devised for the 

 volumetric determination of the organisms actually eaten during 

 comparable periods of time. The result of this work, which has been 

 carried on at intervals for several years by the author and Mr. T. E. B. 

 Pope, has shown that while the quantity of water filtered is great, 

 averaging roughly about 30 quarts daily for oysters 4^ inches long, 

 the volume of the living food is insufficient to account for the actual 

 growth of the oyster, making no allowance for the requirements of 

 other vital activities. It appears that finely divided organic debris 

 or detritus, which constitutes the major part of the material ingested, 

 plays a more important role in the oyster diet than has been con- 

 ceded, a view which recently has been advanced by Petersen and 

 Jensen.*' 



a Survey of oyster bottoms in Matagorda Bay, Tex. By H. F. Moore. Report of the Bureau of Fish- 

 eries, 1905. Bureau of Fisheries Document No. 610. 



b Volumetric studies of the food and feeding of oysters. By IT. F. Moore. (Proceedings of the Fourth 

 International Fishery Congress, Washington, 1908.) Bulletin, Bureau of Fisheries, vol. xxvra, 190«, pp. 

 1295-1308. 



c Valuation of the sea. L— Animal life of the sea bottom, its food and quantity. By C. G. Joh. Petersen 

 and P, Boysen Jensen, Report of the Danish Biological Station, XX. Copenhagen, 1911. 



