Physiological effects of hydrocarbons on the marine diatomCyclotella cryptica

Effects of hydrocarbons on the marine diatomCyclotella cryptica have been studied in laboratory experiments. Low hydrocarbon concentrations (100 μg· l(-1)) stimulate growth whereas higher concentrations (l mg· l(-1)) inhibit growth. The aromatics are most toxic among the hydrocarbons, whereas the paraffins do not seem to have any serious effect on growth or photosynthesis of the algae. Both aromatic and paraffin fractions affected the chlorophyll a, protein, and sugar contents of the cells. Toxicity levels were affected by the presence of dissolved organic material in the medium. Studies on the ultrastructure ofC. cryptica have shown that paraffins affect the thickness of the cell wall.