GROWTH OF A COCCOID NANOPLANKTER (EUSTIGMATOPHYCEAE) FROM THE CHESAPEAKE BAY AS INFLUENCED BY LIGHT, TEMPERATURE, SALINITY AND NITROGEN SOURCE IN FACTORIAL COMBINATION1

Abstract

ABSTRACTDivision rates of Nannochloris oculata Droop (Chesapeake Bay clone) were recorded in semicontinuous cultures grown at 81 combinations of light intensity, temperature, salinity and nitrogen source. A maximal growth rate of 2.1 doublings 1 day occurred at 30 C, 15‰ salinity with a light intensity of 11,300 lux (1.350 mW/cm2) using ammonium or urea as nitrogen sources. Several generalizations about the autecology of this organism result: (1) salinity optima were between 5–15‰ in all instances. (2) the lack of growth at 10 C and the universal improvement in growth with temperature elevation to 30 C indicates a rather high temperature optimum. (3) there is a trend of decreasing light optimum with temperature decreases below the optimum.The source of nitrogen providing the best growth was shown to be dependent on light, temperature, salinity and interactions among these variables. For nitrate and ammonium cultures, temperature had the greatest influence on growth rate, followed by light and then salinity. For urea cultures, the order was temperature, salinity, then light. Interactions of all combinations of variables were significant with the temperature‐salinity‐light interaction most pronounced with urea cultures. Demonstration of interactions among environmental variables and nitrogen nutrition suggests that some conclusions based on surveys employing fixed variables alone may be unreliable.