E. M. Kindle — Bottom Control of Marine Faunas. 459 



objects for attachment may be cited as a further illustration of 

 this poiut. Keller* has observed 350 young oysters attached 

 to a shell-surface 2 by \ inches, while soft mud bottom without 

 solid objects is always barren of oysters. 



It may be noted here that it is not the sedentary forms of 

 life alone which are controlled in their distribution by the 

 physical character of the bottom. It has long been known to 

 deep-water fishermen that successful fishing was limited to a 

 large degree to certain kinds of bottom. Ichthyologists are 

 well aware that large schools of fish make their habitat over 

 certain types of bottom and the D. S. Fish Commission includes 

 in some of its recent reports, mapsf showing the physical char- 

 acteristics of the sea bottom on the continental shelf which are 

 intended for the guidance of fishermen in selecting profitable 

 fishing grounds. With reference to sand bottom these authors 

 state that " no halibut fishing of consequence is to be expected 

 on continuous fine grey sand bottom.":}; Again they remark 

 that "ordinarily this kind of bottom (grey sand) does not carry 

 fish."§ Gravel bottom and "broken bottom-' composed of 

 shale gravel, sand and mud in patches these authors speak of as 

 "rich bottom" over which good catches of fish are to be 

 expected. It is thus evident that the character of the bottom 

 controls the distribution not only of the attached and sedentary 

 forms of life but in large measure the free swimming forms as 

 well. 



The rate of sedimentation is another factor connected with 

 bottom conditions which is important in limiting the habitat of 

 attached invertebrates. A deposit of 12 inches of mud in four 

 days on a freshly prepared oyster bed has been reported! on 

 the Gulf coast. No colony of attached shells could survive 

 this rapid rate of sedimentation. 



Bottom Compared with Latitude Control. 



The high efficiency of bottom control of the composition of 

 a faunal congeries is clearly indicated when compared with the 

 effects resulting from differences in latitude on the composition 

 of a fauna which are well known to be considerable. The 

 contrast in composition between the Bay of Fundy Molluscan 

 fauna and that of N. Labrador may be taken as an illustration 

 of the influence of latitude in modifying faunal composition on 

 the east coast of Canada. Through the labors of a number of 

 workers extending over three-quarters of a century, the 



'* Louisiana Gulf Biological Station, Bull. 3. p. 28, 1905. 



fW. L. Scliinidd, E. C. Johnston, E. R. Rankin and E. Driscoll. Survey 

 of the Fishing grounds on the coasts of Washington and Oregon in 1914. 

 Rep. U. S. Comm. of Fisheries for 1914 (1915), Appendix VII, pp. 1-80. 



J Ibid., p. 21. grind., p. 19. 



Idem., p. 37. 



