ROLE OF THE BOTTOM FAUNA IN THE 

 PRODUCTIVITY OF LAKES'^ 



By FRANK E. EGGLETON 



DEPARTMENT OF ZOOLOGY AND UNIVERSITY BIOLOGICAL STATION, 



MICHIGAN, ANN ARBOR, iriCII. 



UNIVERSITY OF 



Introduction 



Ix the niieroeosinic eeoiiomv of a lake, 

 each division of the inanimate habitat, each 

 category of environmental factors, each 

 realm of the biota, forms a structural and 

 functional part of the composite whole. If 

 any one characteristic of lacustrine ecology 

 is more often apparent to tlie limnologist 

 than any other, it is this interdependency 

 of the physical, chemical, and biological 

 phenomena whose constant interplay weaves 

 a complex design in the fabric of the life of 

 inland waters. The behavior pattern of 

 organisms is everywhere determined by the 

 stimuli which impinge upon them. These 

 stimuli are, in their turn, conditioned by 

 the intrinsic nature of that division of the 

 inanimate habitat within which an organ- 

 ism lives. 



Beneath the waters of a lake lies one of 

 the two major categories of lacustrine habi- 

 tats, the lake floor. There, as elsewhere, the 

 effectiveness with which environmental fac- 

 tors play upon the inhabiting organisms 

 is modified by the particular nature of the 

 immediate environment. Forces inherent 

 in the nature of the substratum itself bend 

 and shape all other forces and thus condi- 

 tion the reactions of the biota. Life in the 

 realm of the benthos is complex, variable, 

 and intricately interwoven with that of the 

 lake as a whole. 



Although it is perfectly proper thus to 

 refer to the entire lake floor as one great 

 subdivision of acpiatic habitats, it is not to 

 be supposed that there is any marked uni- 

 formity of detail in the conditions of ex- 

 istence over the whole basin. Diversity is 

 one of the chief characteristics of fresh- 



* Contribution from the Department of Zoology 

 and from the Biological Station of the University 

 lof Michigan. 



water situations and the benthic type of 

 habitat is no exception to the general rule. 

 ]\Iany of the most potent environmental fac- 

 tors vary markedly with depth and this 

 fact has served as the basis for what is 

 undoubtedly the most widely accepted clas- 

 sification of benthic zones. 



Several systems have been proposed at 

 various times but within the last decade the 

 one wliieh has come to enjoy nearlj^ uni- 

 versal acceptance divides the lake floor into 

 three major zones, the littoral, sublittoral, 

 and profundal. A fourth major zone, the 

 abyssal, proposed at an earlier date, has 

 found little favor and less application. 

 This fate seems only natural from the fact 

 that its sponsor proposed to limit it to those 

 great depths, as fresh waters go, below 600 

 meters. It may be that when the two or 

 three lakes in the world known to have such 

 tremendous depths are more adequately 

 studied we shall have need for the term. 

 Until then the mere fact of depth alone 

 seems insufficient reason for applying it. 

 Unless some significant change can be 

 shown to occur in the benthic habitat or 

 the benthic fauna at that or some other 

 depth there seems small justification for 

 setting off the abyssal from the deeper pro- 

 fundal. 



Although limnologists have very gener- 

 ally accejDted this terminology for the ben- 

 thic zones, they have been far less in agree- 

 ment concerning the exact definitions and 

 limitations of the terms. In 1931 the 

 speaker proposed certain definitions which 

 have enjoyed some degree of acceptance. 

 They were stated as follows : 



"... the littoral zone of the bottom is 

 . . . that region h'ing between the shore- 

 line and, approximately, the lakeward 

 limit of (rooted) aquatic vegetation. The 



11^3 



