SOME RELATIONSHIPS OF PHYTOPLANKTON TO 

 LIMNOLOGY AND AQUATIC BIOLOGY 



By G. W. PRESCOTT 



ALBION COLLEGE, ALBIOX, MKII. 



The history of liinii()lo<iy and tlie <iroAvth 

 of the science of lake biology have been, 

 from the very start, so completely inter- 

 woven that the tAvo cannot even be thought 

 of separately. There is no intention in this 

 paper to deal with the history of onr knowl- 

 edge of lake phytoplankton, but to do so 

 would be very interesting* and illuminating. 

 Such an examination would, for example, 

 serve to establish an understanding of the 

 present complete dependence of phyto- 

 plankton ecology on limnology, and at the 

 same time would point out the many ways 

 in which limnology has come to take count 

 of phytoplankton and other aquatic plants. 



Although biologists in the last part of the 

 nineteenth century appreciated the deter- 

 mining influence of lake chemistry on the 

 composition of acjuatic populations, it was 

 not until the early ]iart of the twentieth 

 century that correlations began to be under- 

 stood and critically discussed. Limnologi- 

 cal studies, especially those made during the 

 past two decades by Birge and Juday, G. M. 

 Smith, Pearsall. Thienemann, Naumann, 

 Wesenberg-Lund, Welch, Strom, Hutchin- 

 son, AViebe, Huber-Pestalozzi, and many 

 others, have resulted in the accumulation 

 of an enormous amount of data. 



In this paper the term plxytoplankion will 

 refer oidy to algal floras, although we are 

 well aware that certain phanerogamic 

 plants may constitute important plankton 

 components. The presence of a plankton 

 flora in a lake sug-gests biological problems 

 as intrig-uiug as, or even more so than, those 

 of a land flora. These problems, both of 

 purely scientific interest and also of well- 

 recognized practical importance, are many 

 indeed, and only a few can be considered 

 here. 



It is obvious that these problems usually 

 resolve about some phase of plant ecology, 



although taxonomy nnist of necessity serve 

 as a systematizing- basis for our knowledge. 



When a plant known only from lakes of 

 the Alps, or from Brazil, is next found in 

 western North America or New England, 

 or, when an association of phytoplankton 

 species is found to have a world-wide lati- 

 tudinal distribution, certain questions nat- 

 urally come to mind. One of these is, of 

 course : What do the lakes in Brazil have in 

 conunon with those of New England which 

 permit a certain species to thrive in them 

 and not in others? Or, what are the factors 

 which provide for a geographical distribu- 

 tion of a phytoplankton association? 



Certainly the cosmopolitan distribution 

 of many phytoplankters and the wide dis- 

 tribution of little-known or apparently rare 

 species is good evidence that there has been 

 ample time and opportunity for a much 

 more equal distribution of algal species than 

 we now find. In other words, if time and 

 means of translocation were the only factors 

 involved, we might well expect to find 

 nearly the same species of plants in all lakes 

 throughout the world. We do not, of 

 course ; and the reasons why we do not are 

 to be found in the combinations of limno- 

 logical factors which determine aquatic 

 flora and fauna. In fact, we learn from 

 limnology that lakes are even more exacting 

 of their biota components than terrestrial 

 habitats. 



While we can follow Thienemann in his 

 classification of lakes, we realize that each 

 lake is an individual entity, a point which 

 cannot be overemphasized. The many in- 

 teracting factors of an aquatic environment, 

 many of which are based upon or are related 

 to the underlying or surrounding physio- 

 graphic features as well, provide for innu- 

 merable types of habitats. Each lake rep- 

 resents a special and jiarticular combination 



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