Abstract

The effects of food concentration and food quality on the growth rate and bioluminescence potential of the heterotrophic dinoflagellate Noctiluca scintillans were examined. The growth rate of N. scinullans varied greatly with the phytoplankton food it was provided, and those foods yielding higher growth rates also produced cells that were smaller in diameter, but with a greater bioluminescence potential per unit volume. Small phytoplankton species, including Isochrysis galbana and an unidentified chrysophyte responsible for the Texas brown tide, supported the lowest growth rates. Other small flagellates (Dunaliella tertiolecta) and dinoflagellates (Gyrodinium dorsum, Prorocentrum minimum) supported moderate growth rates. The highest growth rates were supported by diatoms and prasinophytes. Maximum growth rates (0.5 day^-1) were obtained with the diatom Thalassiosira sp. at concentrations ij0 5 mg C 1^-1. Cells both larger and smaller in size than Thalassiosira sp supported lower growth rates at 1 mg C 1^-1. Most mixtures of two foods showed no enhancement of growth compared to equivalent concentrations of either food alone. The brown tide chrysophyte had a negative effect on the growth of N scintillans. There was no significant relationship between growth rate on different phytoplankton foods at 1 mg C 1^-1 and total bioluminescence per cell at the end of the growth experiments, but growth rate was significantly correlated with bioluminescence per unit volume of N.scintillans, faster growing cells were smaller and had more bioluminescence per unit volume