Ecological Systems and Devices Annotation << Back INTERACTION OF MICROALGAE IN A MIXED CULTURE DURING INTOXICATION WITH DIFFERENT DOSES OF CHROMIUM V.I. Ipatova, M.A. Mikheev The interaction of two species of microalgae Scenedesmus quadricauda (Turp.) Breb. and Monoraphidium arcuatum (Korsch.) Hind. in a mixed culture was studied at different levels of exposure to chromium in the composition of potassium dichromate – low, medium and high concentrations of the toxicant in chronic experiments. The most integral test parameter in bioassay using mixed cultures of microalgae is the number of cells, which makes it possible to take into account the ratio of individual species. It was shown that the sensitivity of each species in a monoculture is higher than in a mixed culture in both acute (3 days) and chronic (31 days) experiments. In a mixed culture, at low levels of dichromate exposure (1–3 mg/l), M. arcuatum is more sensitive to competitive displacement by S. quadricauda, and at high levels (5–10 mg/l), M. arcuatum becomes more resistant to competitive exclusion over a long period of time. Such an effect of the action of a toxicant on a two-species test system should be taken into account for a more adequate assessment of the toxicity of substances for microalgae. The data obtained indicate that single-species bioassays in standard biological assays may underestimate the toxicity of metals in natural waters. Keywords: mixed culture, Scenedesmus quadricauda, Monoraphidium arcuatum, biotic interaction, bioassay, potassium dichromate. DOI: 10.25791/esip.2.2023.1354 Pp. 36-45.