Influence of organic compounds and light limitation on the growth rate of estuarine benthic diatoms

Ten species of benthic diatoms from the Eems-Dollard estuary were grown in axenic cultures under various combinations of irradiance and supply of organic substrates. Six species were capable of growth in the dark on yeast extract, casamino acids, or glucose. Four of these species grew best in the presence of glucose, whereas the growth of the other two species was supported only by yeast extract and casamino acids. The light limited growth rate of only those species that were also capable of heterotrophic growth in the dark was increased by organic substrates. The rate of this “mixed” growth together with the absence of a lag-phase upon change from autotrophic to heterotrophic conditions indicates the nutritional versatility of these diatom species. A positive relation between the organic matter content of the natural habitat and the heterotrophic capacities of the diatom species is suggested. All species with heterotrophic capacities were isolated from muddy sediments, whereas two species isolated from a sandflat seem to be obligately autotrophic. Also two species from muddy sediments apparently had no heterotrophic capacities. The cells of the six species with heterotrophic capacities differed from those of the four species without such capacities in their higher surface to volume ratio.