BOTTOM FAUNA IN THE PRODUCTIVITY OF LAKES 



127 



little mention of the phenomenon seems to 

 have been made before that date. Adam- 

 stone and Harkness (1923) and Adamstone 

 (1924:) reported on their stndies of the bot- 

 tom fanna in Lake Nipigon and their re- 

 sults plainly showed a concentration zone 

 in that lake. Lnndbeek's work (1926) 

 demonstrated a sharply defined concentra- 

 tion zone in many of the northern German 

 lakes. Kawsoii (1928, 1930) in excellent 

 reports on the bottom fanna of Lake Simcoe 

 described the same characteristic of depth 

 distribution of the beuthic fauna and like 

 Lundbeck discussed the phenomenon in re- 

 lation to environmental factors. Since that 

 time the same type of depth distribution 

 has been reported from many lakes in 

 Europe, Asia, and North America. Re- 

 cently, it has been shown (Eggieton 1936, 

 1937) that the distribution of the benthos 

 on the floor of Lake ^Michigan exhibits the 

 same feature. This investigation extended 

 over a six-month period during each of two 

 consecutive years and in ' ' Each year a pro- 

 nounced concentration zone was present be- 

 tween 35 and 50 meters with its peak close 

 to the 42-meter level in both seasons." 

 Miyadi, in his extensive series of bottom 

 fauna studies on Japanese lakes, not only 

 clearly demonstrated a concentration zone 

 but also reported additional interesting 

 observations which have contributed much 

 to our growing understanding of the ecol- 

 ogy of the benthos. 



Introduction of Ekman's dredge, as has 

 been intimated, marked a milestone in the 

 development of beuthic biology. Neverthe- 

 less, as it was first introduced a rather seri- 

 ous sampling error was inherent in the 

 apparatus. The modification now known 

 as the Ekman-Birge dredge largely cor- 

 rected this situation and out of this fact 

 there later developed an increasing interest 

 in the vertical distribution of the beuthic 

 animals within the substratum. Many 

 authors have discussed the matter and still 

 more haA^e offered data j^ertinent to the 

 question but no exhaustive study of the 

 problem has yet been made. Probably the 

 best single contribution to this subject is 

 that of Lenz (1931) who investigated this 



vertical distribution by means of specially 

 designed apparatus. In most lakes of 

 northeastern United States which the 

 speaker has had an opportunity to observe 

 the macroscopic animals are almost wholly 

 confined to the upper few centimeters of 

 deposit. The depth to which they pene- 

 trate depends on several factors, but proba- 

 bly most of all on character of the deposit 

 itself. Moore (unpublished) found several 

 very interesting and surprising things in 

 connnection with the vertical distribution 

 of the microscopic fauna within the pro- 

 f undal muds of Douglas Lake. Still further 

 work is needed in this subject. 



Conditions of existence within the bottom 

 deposits are probably more stable than with- 

 in the limnetic regions just above. And 

 yet in the bottom sands and muds the en- 

 vironment is never quite at rest. Seasonal 

 changes in the atmospheric climate produce 

 profound effects in the ambient medium of 

 the limnetic zone of our temperate and 

 polar lakes and these changes in the super- 

 imposed water, in turn, strongly affect life 

 in the bottom deposits. These changes are 

 strikingly reflected in the seasonal varia- 

 tions of the fauna and again take the two 

 forms, qualitative and quantitative. In typ- 

 ical eutrophic, temperate lakes of the sec- 

 ond order, for instance, the qualitative com- 

 position of the beuthic fauna will vary 

 considerably with the seasons at any par- 

 ticular IcA'el and likewise in such a lake 

 there are often enormous fluctuations in 

 terms of the numerical abundance of the 

 individuals of the constituent species. To 

 cite but one example, the author found that 

 the prof undal beuthic fauna of Third Sis- 

 ter Lake within the 18 meter contour varied 

 qualitatively from a maxinuim of six or 

 seven species in spring and fall to two or 

 three in midsummer or midwinter stagna- 

 tion and quantitatively from about 1,500 to 

 more than 70,000 individuals per square 

 meter. It should be pointed out in passing 

 that one of the prime causes for this tre- 

 mendous quantitative variation is the phe- 

 nomenon of emergence in the life cycle of 

 the predominant insect members of the 

 fauna. 



