larger phytoplankters have been excluded from the diet of experi- 

 mental animals such as Calanus (Clarke and Gellis, 1935). 



Furthermore, other researchers have indicated that the concentra- 

 tion of dissolved and colloidal matter used in the culturing of lab- 

 oratory animals was greater than the normal concentration of these 

 substances in nature which is supposedly not sufficient to maintain 

 microfaunal populations. Thus the burden of direct support is 

 thrown back on the phytoplankton. 



It is noteworthy that although the idea that phytoplankters are im- 

 portant in the food chain is apparently sound and generally accep- 

 ted, it is borne out by relatively few published scientific observations. 

 It is evident that there is much to be learned in this connection, and 

 the question certainly merits considerable attention both in the field 

 and in the laboratory. This is especially true, since so many predic- 

 tions and evaluations of productivity are based, in part, on the as- 

 sumption that phytoplanktonic components in the biota are of basic 

 importance in the food chain. A clear understanding of the exact 

 nature of this problem must be reached before the quality and quan- 

 tity of phytoplankton can be used as dependable indices of pro- 

 ductivity. 



There are many published studies bearing out the correlation 

 between seasonal maxima in phytoplankton and peaks in microfau- 

 nal populations. The inference usually drawn from this correlation is 

 that the increased phytoplankton makes possible a larger microfau- 

 nal foraging population, which in turn would support a more 

 numerous macrofauna. But it is not known whether the microfauna 

 achieves maxima after a peak in the phytoplanktonic population 

 because it feeds directly on the plants, or because it is nourished by 

 particulate matter resulting from the plants' disintegration. 



Whatever the precise relationships are between the algae and the 

 eventual productivity of fish and other animal life, it is well known 

 that lakes with a luxuriant flora maintain a correspondingly dense 

 population of animals. This relationship is illustrated many times 

 over in lakes of the Michigan and Wisconsin area. Post Lake, Lang- 

 lade County, Wisconsin, for example, and Ocqueoc Lake, Michigan, 

 are highly productive and excellent for game fish, as many as eight 

 species occurring in the former. These are medium hard water lakes 

 and characteristically support a luxuriant vegetation of both algae 

 and larger aquatic plants. Chara spp. abound, and the phytoplank- 

 ton approaches the cyanophyte-diatom type. Near Post Lake is 

 Elcho Lake, in which perch is the only game fish on record, and 

 which has a poor phytoplanktonic flora and scarcely any larger vege- 

 tation, as compared with Post Lake. 



[46] 



