FISHERY BULLETIN: VOL. 70, NO. 4 



fi = 0.851 (1.066)' 



(la) 



McLaren (1963) discussed the choice of a tem- 

 perature function and preferred the formula of 

 Belehradek 



DetonulQ confervacea 



H- 



a (T — a)' 



(lb) 



where a, b, and a are constants. A virtue of 

 this equation, among the three monotonic func- 

 tions discussed by McLaren (1963) is that a, 

 the scale positioning factor, represents a "bio- 

 logical zero" for the process. A graph of log (/x) 

 vs. log (T — a) assumes linearity for appro- 

 priate values of a. Fitting values from Equa- 

 tion (1) at T = 0, 10, 20, and 30 degrees gave 

 linear graphs if a were ^ — 40 degrees. For 

 a — — 40, a and b were approximately 2.46 X 

 10~^ and 3.45, respectively. 



Figure 1 can be made more understandable by 

 comparing fx vs. temperature curves for a few 

 selected species for which fairly complete data 

 are available (Figure 2) . Each of these species 

 has a different optimum temperature and the 

 maximum growth rate for each approaches the 

 line of maximum expectation. Such "fx vs. tem- 

 perature" curves typically show a gradual di- 

 minution of fx as temperature decreases from the 

 optimum, but an abrupt decline at supraoptimal 

 temperatures. 



Temperature optima and the upper critical 

 temperature can be shifted somewhat by alter- 

 ing environmental conditions. For example, the 

 salinity of the culture medium influences these 

 parameters in euryhaline Dunaliella tertiolecta 

 (Figure 3). Note, however, that only one salt 

 concentration gives the unique maximum growth 

 rate of about 5.0 doublings/day. 



The figures can be criticized as being limited 

 with respect to the number of species included. 

 Furthermore many of them represent "labora- 

 tory weed" species and relatively few are ecolog- 

 ically significant ocean phytoplankton. Happily 

 this shortcoming is temporary and information 

 on important planktonic species is growing (see 

 Figure 1 legend). 



Use of Figures 1 and 2 or Equation (1) for 

 insight as to maximum expected values of /a in 

 the sea presumes that natural marine phyto- 

 plankton are autotrophic. But it is conceivable, 



o 



T3 



< 



5 



o 



20 30" 



TEMPERATURE 



40 



50 



Figure 2. — Growth rate vs. temperature curves for five 

 unicellular algae with different temperature optima: 

 Detonula confervacea (Guillard and Ryther, 1962; 

 Smayda, 1969), Skeletonema costahnn (Jorgensen, 

 1968), Dityhnn brightwellii (Paasche, 1968), Dunaliella 

 tertiolecta (McLachlan, 1960; Ukeles, 1961; Eppley, 

 1963; Eppley and Sloan, 1966), Chlorella pyrenoidosa. 

 (Sorokin and Krauss, 1958, 1962). 



although perhaps unlikely in the sea, that hetero- 

 trophic nutrition might lead to values of /-t 

 higher than predicted above, as appears to be 

 the case when one compares doubling times of 

 heterotrophic and photosynthetic bacteria or 

 autotrophic vs. photoheterotrophic growth rates 

 of the sewage alga Chlamydomonas mundana. 

 Equation (1) has been useful in this labora- 

 tory for predicting the maximum dilution rates 

 ("washout rates") for continuous cultures. In 

 the few organisms examined here the value of 

 fjL at washout was slightly higher than the max- 

 imum rate observed in batch cultures of the or- 

 ganism, but within the envelope of values pre- 

 dicted by Equation (1). 



1066 



