STUDIES ON THE AUTECOLOGY OF THE MARINE DIATOM <i>THALASSIOSIRA NORDENSKIÖLDII</i>
CLEVE. 1. THE INFLUENCE OF DAYLENGTH, LIGHT INTENSITY, AND TEMPERATURE ON GROWTH¹

Abstract

SUMMARY The marine diatom Thalassiosira nordenskiöldii Clave was grown at 48 different combinations of daylength (9:15, 12:12, 15:9 LD), light intensity (0.011, 0.027, 0.066, 0.100 ly/min [g cal/cm 2 /min]), and temperature (0, 5, 10, 15 C). Growth occurred at all combinations of light and temperature except at 15 C at the highest light level. Maximum growth ( K = 1.8 doublings/day) occurred at 10 C under the 15:9 LD cycle. At 15 C the maximum rate was 1.7 doublings/day but occurred at the shortest day‐length (9:15 LD). The maxima at 5 and 0 C were 1.32 and 0.67 doubling/day, respectively. At 0 C growth was similar over a wide range of light intensities ( K = 0.6–0.65), with, maximum growth being attained at a much lower light intensity than at 5 C. Above 5 C there was a decrease in the light intensity at which maximum growth occurred and excessive light became inhibitory to growth. At 15 C the light intensity at which maximum growth occurred was greater with shorter day‐lengths. The temperature optimum was 10 C at 15:9 and 15 C at 9:15 LD. The chlorophyll a content of the cells was greatest under low light intensities and short daylengths, while temperature had a variable effect. The response of Thalassiosira in the laboratory contrasts with, its apparent preference for low temperatures in nature (0–5 C). The experiments suggest that the termination of the bloom of Thalassiosira in Narragansett Bay and elsewhere is not solely temperature dependent.