no Roosevelt Wild Life Bulletin 



lake under fall conditions the temperature of the water again becomes 

 unfavorable. In general, optimum temperatures for the growth of 

 the different classes of algae are different. The diatoms (Pis. 23- 

 24) generally have two periods of maximum growth, one in the 

 spring and another in the fall. Although other factors influence 

 their growth, temperatures between 50° and 60° F. are found when 

 they are most abundant. The relation of the grass-green algae 

 (Pis. 7-22) to temperature is less certain, but their optimum is 

 somewhere between that of the diatoms and that of the blue-green 

 algae. Temperatures favorable for the growth of grass-green algae 

 generally occur twice a year in the periodic temperature cycle of 

 lakes, but large growths of these algae are usually found only in 

 the late spring or early summer, possibly because the gas content 

 of the lakes is not right in late summer v/hen temperatures are also 

 favorable. Broadly speaking, the blue-green algae thrive best at 

 summer temperatures. Wesenberg-Lund ('04) finds that in the case 

 of the filamentous blue-green algae (PI. 4, Figs. 3-6) there are 

 rather close limits for the various species found in Danish lakes, 

 and that certain species are most abundant when the temperature 

 is i6-ti8° C. while others reach their maximum growth at 18-22° C. 

 He maintains that temperature plays an important role in blooming, 

 and that those species that require warm midsummer temperatures 

 of the water for maximum growth do not appear in quantity in 

 cool summers when the temperature of the water does not rise above 

 18° C. Not all blue-green algae, however, reach their maximal 

 development at high temperatures, the most notable exception being 

 the alga which produces the " Burgundy bloom " in Swiss lakes at 

 a temperature near the freezing point, and which disappears as soon 

 .as the water becomes warmer (Bachmann, '10; Lozeron, '02; 

 Schrdter, '97). 



ECOLOGICAL RELATIONS OF THE SPHYTOPLANKTON OF THE PARK 



The Nature of the Plankton Flora. Before considering the 

 ecology of the phytoplankton in the Park, attention should be called 

 to the fact that the phytoplankton forms a definite plant association 

 and not an accidental heterogeneous collection of algae that grow in 

 mid-lake. In a collection of algae from mid-lake the greater part 

 of the individuals are those to be found only in the plankton and not 

 in the shore flora; there are, however, a small proportion of shore 

 forms that have drifted out into the open lake. The former have 

 been called the eulimnetic phytoplankton and the latter the tycho- 

 limnetic. There is still another group of algae which thrive equally 

 well under shore (benthitic) or true plankton (pelagic) conditions, 

 and for which I have suggested the name: facultative planktonts, 



Recognition of the distinctive nature of the eulimnetic plankton 

 community is necessary, since many investigators in discussing the 

 origin of the plankton constituents of a reservoir or an artificial 

 lake assume that the " seeding " comes from the algae associated 

 with the vegetation of swamps or streams draining into a lake. 



