Limiting nutrients and maximum growth rates for diatoms in narragansett bay

Abstract

Dialysis cultures of Skeletonema costatum (Grev.) Cleve and Asterionella japonica Cleve & Möller ex Gran were grown in tanks in running sea water pumped from a depth of 6 m during March–June, at 50 % of the surface light intensity and at a temperature range of 2–17 °C. The exponential growth rate was exponentially related to temperature at surface light intensities of 350–500 ly day −1, with a maximum of 2.0 div. day −1 for Skeletonema and 1.9 div. day −1 for Asterionella at 17 °C. Surface light intensities below 200 ly day −1 give a decrease in the growth rate. The growth rates found for Skeletonema seemed to encompass all those measured in the Bay, the maximum ones in the Bay being close to those observed in the dialysis cultures. All cultures showed clear physiological signs of nitrogen deficiency, as indicated by changes in the ratios between chlorophyll a, ATP, nitrogen and carbon, when going from the exponential phase to the starvation phase. The chl ATP ratio showed a 4-fold temperature-dependent increase from March to June for both starved and exponentially growing cells of both species. In Skeletonema, this was mainly due to an increase in chlorophyll content, but in Asterionella to a decrease in ATP which was accompanied by a decrease in carbon per cell. A comparison of dialysis-cultured populations of Skeletonema ( t = 17 ° C, μ = 2.0 div. day −1) and a natural population of the same species ( t = 15 ° C, μ = 1.8 div. day −1) showed that they were identical in chemical composition.