BOTTOM FAUNA IN THE PRODUCTIVITY OF LAKES 



125 



shallow regions, have long* been known. 

 IMoreover, P^orel and other early workers 

 knew something abont a deep-water fanna, 

 althongh they probably did not realize the 

 existence of a profundal bottom fauna as 

 a group of distinct ecological communities. 

 The equipment available to early limnolo- 

 gists determined the fact that all the pio- 

 neer work on benthic organisms was strictly 

 cpialitative. It was not until 1911, when 

 Ekmaii introduced the dredge which now 

 bears his name, that work in this field be- 

 came quantitative ; and until about 1920 

 one could count all the truly significant 

 studies in this branch of limnology on the 

 fingers of his two hands. 



During the latter decades of the last cen- 

 tury the early workers in fresh-water biol- 

 ogy, employing the methods of oceanogra- 

 phy, made some exploratory studies of the 

 deep-water fauna in various lakes both in 

 Europe and in America. Their equipment 

 and methods precluded any possibility of 

 distinguishing clearly between those organ- 

 isms which lived in the bottom deposit and 

 those which lived in the open water just 

 above it. The concept of a deep-water ben- 

 thic fauna as a distinct animal association 

 did not emerge, therefore, until after 1900. 

 While Forel was laying the foundations for 

 investigations of bottom fauna in Europe, 

 beginning about 1870, Stimpson, Hoy, 

 Smith, Verrill, and others began publica- 

 tion of the pioneer American work in the 

 same year. During the next 40 years, both 

 in America and in Europe, a rising tide of 

 interest and activity marked the develop- 

 ment of limnology generally and as a part 

 of the rest there were scattered studies of 

 deep-water organisms and several investi- 

 gations which included some qualitative 

 enumerations of true benthic forms. The 

 first decade of the present century saw the 

 publication of the first research which was 

 restricted specifically to bottom fauna. The 

 work of Ekman and the introduction of his 

 dredge in 1911 added a considerable impe- 

 tus to this phase of limnology. However, 

 before the effect could become conspicuous 

 most of the world became concerned with 

 more compelling but much less profitable 



business. Beginning again just after the 

 war, publication has continued at a con- 

 stantly accelerating rate and during the 

 past 20 years scores of investigators have 

 published literallj- hundreds of papers on 

 the benthic fauna in at least 15 languages. 

 Todaj' there are two well-defined aspects 

 of emphasis in limnology generally, and 

 this fact is also quite evident in benthic 

 studies. Fisheries interests, federal bu- 

 reaus, and the state and regional surveys 

 are accentuating the applied aspect and 

 along with this there is, as always, the basic, 

 fundamental research. Let me hasten to 

 add, that no one need fear exhaustion of 

 the subject because of this activity. To 

 those of us who study in this field it is 

 increasingl,y apparent that we have only 

 begun to open the way for a tremendous 

 amount of research that needs to be done. 



The Benthic Fauna 



When considered from the edge of the 

 water to the greatest depths and in all 

 types of lakes, the benthos comprises repre- 

 sentatives from nearly every phylum of 

 animals which occurs in fresh waters at all 

 and from practically all of the larger plant 

 groups. The animals are as diversified 

 morphologically and in habits as they are 

 taxonomically. They vary from those 

 which spend only a small part of their life 

 cycle within the bottom deposits to those 

 which have their whole existence in that 

 habitat. Some are exceedingly active, 

 others are sluggish and sessile. Many build 

 tubes, or cases, or shelters of other sorts, 

 but still more dwell unprotected in the soft 

 mud beneath quiet waters. The situations 

 they choose and the types of substratum 

 which they select range from torrential 

 streams to the stagnant depths of stratified 

 lakes and from flat rocks and great boulders 

 through rubble, gravel, sand, and clay to 

 the soft, semi-flocculent ooze within the pro- 

 fundal zone of many large lakes. 



Of the many ways in which it is possible 

 to classify these animals, one of the simplest 

 and most used, although intrinsically arti- 

 ficial, methods is on the basis of size alone. 

 This division has arisen from the practice 



