Abstract

We examined the response of diatoms to naturally experienced temperatures and tested these hypotheses: (1) diatoms follow the rule that organism size decreases with increasing temperature; (2) diatom growth rate follows a Q1O-like response; (3) diatom carbon (C) and nitrogen (N) content per unit volume (V) decrease with increasing size, and changes in temperature affect this relationship; and (4) diatom C: V is the same as that of other phyto- plankton. We also present, as predictive equations, relationships between (1) growth rate, temperature, and size; (2) C content and V; and (3) N content and V. Eight diatoms and two flagellates were acclimated for approximately five generations and grown for approximately five more generations at five temperatures (9-25°C) on a 14: 10 light: dark cycle at 50 ,umol photons m-2 s-l. Growth rate, cell V, and C and N content per cell were measured; relationships between these parameters and temperature were determined. For five diatoms and both flagellates, cell V decreased with increasing temperature; cells decrease by 4% of their mean V per °C. Growth rate appeared to increase linearly with temperature in all cases. The literature suggests that a linear response is the rule, not the exception. Temperature did not significantly affect C or N per V of diatom species. When all diatoms were con- sidered, both C and N per V decreased with increasing cell size; our data support the argument that diatoms differ from other protists in this respect, but the difference is less pronounced than stated in previous reports.