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ABSTRACT
An axenic clone of Fragilaria crotonensis was isolated from Lake Erie to quantitatively measure its growth and photosynthetic rates under different light and temperature regimes in the laboratory. Maximum growth (0.54 doublings day−1) and photosynthetic (3.7 mg C 10−9 cells h−1) rates were highest at 23 and 17°C and decreased with decreasing temperature (i.e. 11 and 5°C). Even though temperatures of 11 and 5°C are suboptimal for growth of F. crotonensis, they still resulted in 68 and 31%, respectively, of maximum growth rates at 23 and 17°C. Field data show that the F. crotonensis population in Pigeon Bay withstands an annual temperature variation of greater than 20°C and that at 5°c it achieves densities as high as 25% of maximum summer density. These laboratory and field data give strong support that F. crotonensis is eurythermal. The onset of light saturation of both growth and photosynthesis of F. crotonensis occurred at fairly low irradiances, suggesting that it is adaptable to a low light environment.
