BOTTOM FAUNA IX THE PKODl'CTIVITY OF LAKES 



129 



significance in the ecology of the profundal 

 organisms, although the alternate freezing 

 and thawing, together with the snecession 

 of the quiet of winter and the storms of 

 fall and spring; the cold and darkness of 

 winter and the w^armth and light of sum- 

 mer certainly are calculated to relieve any 

 tedium in life of littoral forms. 



It has been shown repeatedly that ben- 

 thic organisms, like all others, have rather 

 definite optimal ranges for each physico- 

 chemical factor. Probably Liebig's famous 

 "Law of the Mininnim" becomes quite as 

 effective sometimes in the life of benthic 

 animals as it ever is in the life of the plants 

 for whose special benefit it was first pro- 

 mulgated. Studying the profundal bottom 

 animals experimentally both in the lake and 

 in the laboratory the speaker has found 

 them to be susceptible to variations in the 

 physico-chemical factors imposed by the 

 ambient medium in varying degree. Per- 

 haps two of the most interesting results of 

 these studies have been that (1) it is possi- 

 ble to produce conditions resembling those 

 which obtain on the profundal lake floor 

 during prolonged stagnation w'hich are so 

 severe that all the organisms are killed and 

 sometimes possible to find similar condi- 

 tions with similar results in nature, and 

 (2) certain lakes vary so far in this direc- 

 tion even to becoming permanently stag- 

 nant in their profundal zone and hypolim- 

 nion that the result is the production of a 

 veritable biological desert. In this connec- 

 tion certain facts always stand out clearly, 

 namely, no factor in natiu'e ever acts alone, 

 every one always is acting in the presence 

 of all the others ; and usually the effective- 

 ness of variations in one factor is greatly 

 increased when operative in the presence of 

 variations in another. A small decrease in 

 dissolved oxygen will, for instance, often be 

 more deleterious in the presence of a high 

 temperature than a greater decrease in oxy- 

 gen would be if unaccompanied by any 

 such temperature variation. 



Biotie interrelations of the bottom fauna 

 are incompletely known. And much that 

 has been discovered is, for obvious reasons, 

 related to the importance of this association 



as a source of fish food. The interspecific 

 and intraspecific relations within the bot- 

 tom fauna itself remain largely to be dis- 

 closed. Parasitologists have been exceed- 

 ingly busy during the last few decades and 

 have added very significantl}^ to this phase 

 of benthic biology, although here again it 

 has most often been the parasitic embar- 

 rassment of some fish or other vertebrate 

 host, such as man, which has been the real 

 motivation, rather than any altruistic and 

 purely disinterested scientific curiosity con- 

 cerning the biology of benthic invertebrates 

 which has resulted in our enlightenment. 



Among the many purely biotie interre- 

 lationships, about w^hich we know so little, 

 a few phenomena have been given some 

 attention. One of these which may be a 

 potent cause in population fluctuations is 

 migration. In some species the individuals 

 actually change their location on the lake 

 floor to a significant extent, in others the 

 death of many individuals within one 

 stratum and the birth (or hatching) from 

 vast numbers of eggs in other and perhaps 

 successively adjacent zones, or the pupation 

 and emergence of insect members of the 

 fauna, may give the semblance of signifi- 

 cant individual migration when actually 

 jiarticular specimens may have moved little 

 if at all. Such phenomena probably com- 

 bine to cause the shift of the concentration 

 zone up and down the lake floor which 

 occurs in some, perhaps many, of our lakes 

 of this region. The speaker is convinced 

 that insect life cycles, including pupation 

 and emergence, and their relations to and 

 eft'ects upon benthic productivity are inade- 

 ([uately understood and offer a fruitful 

 field of work for some one. 



Food, feeding, predators and enemies, 

 symbiosis, commensalism, and host-parasite 

 relationships all play important roles in 

 relation of the benthic fauna, both within 

 its own ranks and in the larger realm of the 

 life of the lake as a whole. Members of the 

 benthos serve both as food for and as feed- 

 ers on other groups within the lake. IMany 

 of them also stand in the important rela- 

 tionship of detritus feeders and copropha- 

 gous scavengers, thus serving as an indis- 



