130 



PROBLEMS OF LAKE BIOLOGY 



pensable link in the cycle of tlie funda- 

 mental food supply of the microcosm which 

 is their home. 



Benthic Productivity 



Biological productivity has been stated 

 by at least one author (AVelch 1935) to be 

 *'the central influence" of limnology. No 

 one, I am sure, will deny its key position 

 in the complex of lacustrine biology. Vari- 

 ous criteria of productivity may be selected 

 with equal justice. Quite commonly it is 

 assumed that it is to be measured in terms 

 of fish production. That is one satisfactory 

 equivalent. It is quite possible, however, 

 and often useful to think of biological pro- 

 ductivity in terms of the benthic fauna. 

 When so considered the two measures most 

 commonly employed for expression of pro- 

 ductivity', namely standing crop and annual 

 'production may be expressed in terms of 

 kilograms per hectare of dry organic 

 weight ; as crude protein, or available nitro- 

 gen; or as number of individuals per unit 

 area. Whatever the unit or mode of mea- 

 surement it will be found that, as in so 

 many other ways, lakes vary enormously in 

 benthic productivity just as farm land 

 does for wheat or corn. The intricate in- 

 terplay of all the physical, chemical, and 

 biological factors which combine to influ- 

 ence or control benthic productivity pro- 

 vides today, and will provide for many 

 years to come, one of the most interesting 

 and most challenging phases of benthic 

 research. 



The contribution of the benthos to the 

 productivity of the lake as a whole is large 

 indeed, regardless of the criteria selected. 

 Entirely aside from the strategic position 

 occupied by these bottom feeding animals 

 as consumers of otherwise useless and lost 

 food and therefore as important contribu- 

 tors to the maintenance of the cycle which 

 must not run down if productivity is to be 

 kept up, they occupy in their own right a 

 place of significance in the production of 

 the total organic substance present in or 

 produced by the whole lake. One need only 

 mention the tremendous figures of more 

 than 33,000 individuals per square meter 

 found by Juday within the profundal of 



Lake Mendota, or the 71,000, and more, in- 

 dividual macroscopic organisms per square 

 meter in the muddy floor of Third Sister 

 Lake, or the more than 20 kg per hectare of 

 dry organic weight on the floor of Lake 

 Michigan to show that the benthos does 

 contribute significantly to total lake pro- 

 ductivity. 



Future Needs in Benthic Studies 



Scattered throughout the foregoing pages 

 there have been frequent suggestions of 

 problems needing further investigation and 

 offering challenging fields of research. 

 However, several points need yet to be 

 stressed in this connection. There are 

 many unanswered questions awaiting a 

 fertile mind and ambitious hand. Why, 

 for instance, has no one succeeded, unquali- 

 fiedly, in the attempt to rear fresh-water 

 sponges in captivity? How do the pro- 

 fundal benthic animals derive their oxygen 

 for metabolism in an anaerobic environ- 

 ment ? Which if any of the seA'eral sugges- 

 tions offered to explain the diurnal migra- 

 tion of Corethra larvae is the correct one? 

 Does the haemoglobin of Chironomus larvae 

 really serve the organism significantly in a 

 stagnant lake bottom ? One might continue 

 such questions indefinitely, but the few here 

 proposed will illustrate the point. 



Several major phases of lacustrine ben- 

 thic faunal research are wide open fields. 

 The task during the past summer of writing 

 a symposium paper on fresh-water com- 

 munities (Eggleton 1939) brought forcibly 

 to the speaker's mind the great dearth of 

 benthic studies made from the standpoint 

 of bottom animals as members of animal 

 communities. Few if any complete life 

 histories have been worked out for the spe- 

 cies of the benthos. There is still much 

 need for many more long-term qualitative 

 and quantitative investigations. Much of 

 our classification of lake types, biotic forms, 

 environmental regions, habitat groupings, 

 and the like will have to be revised when 

 we have more extensive and adequate 

 knowledge on a wide variety of questions. 

 As has been previously suggested study of 

 the microscopic benthic fauna is practically 

 a virgin territory. Our knowledge of the 



