Effect of zinc sulphate on the growth of mono- and multispecies cultures of some marine plankton algae

Abstract

The effect of zinc sulphate has been investigated in mono- and multispecies cultures of the dinoflagellatesScrippsiella faeroense, Prorocentrum micans andGymnodinium splendens and of the diatomsSchroederella schroederi andThalassiosira rotula. Multiplication rate, in vivo chlorophyll fluorescence, maximum cell densities and Zn-conditioned disturbance of the species equilibrium of the multispecies cultures were used as criteria of sublethal toxic inhibition. In monocultures, the first effect became manifest after addition of 0.01 to 0.1 mg Zn⁺⁺ · l⁻¹. Diatoms proved to be more sensitive than dinoflagellates. In multispecies cultures, the growth of each species depended on the ratio of the inocula. Interrelation between interspecific competition and Zn-caused decrease in the number of algal cells regulated further growth of the cultures. Algal sensitivity to zinc increased with the number of species combined in the test medium: in a 5-species culture sublethal changes appeared already after addition of 0.005 to 0.01 mg Zn⁺⁺ · l⁻¹. In a few cases, interspecific competition depressed the growth of some species to an appreciable extent, even in the control cultures. At the resulting low cell numbers, the effect of zinc became apparent only in higher concentrations from 5 to 10 mg Zn⁺⁺ · l⁻¹. Morphological aberrations became manifest inScrippsiella faeroense and in the diatoms in concentrations from 1 and 0.01 mg Zn⁺⁺ · l⁻¹ respectively. The results show that multispecies experiments are a more sensitive test method for investigating the influence of zinc on plankton algae than are monoculture experiments. In natural plankton communities, however, the toxicity of heavy metals may become effective at considerably lower limit concentrations; this is suggested by the simplified model investigations in the laboratory.