Effects of copper, mercury and selenium on the growth of the marine phytoplankton Pavlova lutheri (Droop) Green and Dunaliella minuta Lerche

Gotsis, Olympia (1980) Effects of copper, mercury and selenium on the growth of the marine phytoplankton Pavlova lutheri (Droop) Green and Dunaliella minuta Lerche. University of Southampton, Doctoral Thesis.

Abstract

The effects of cupric chloride, mercuric chloride and sodium selenite or selenate on the growth of P. lutheri and D. minuta were investigated. Both species were grown in batch cultures in an enriched sea water medium and their physiological responses to the metals were examined over a maximum period of 18 days. The response observed differed with the species and metal(s) involved; 10 ppb of either copper or mercury or 2 ppm of selenium (as Sao ') significantly inhibited the growth of P. lutheri. D. minute was more resistant to all three metals, the concentrations causing slight inhibition of growth being about five times greater. P. lutheri reacted to all the metals tested with an increase in the lag phase, followed by a period of recovery in which the growth rate was not significantly reduced. The final cell yield did not differ significantly from that in a control culture. D.minutareacted to copper and mercury with a significant reduction in growth rate and final cell yield. Both copper and mercury increased the mean cell size in both species and caused a lose of motility of cells especially in the early stages. The presence of EDTA in the medium significantly reduced the toxicity of copper, but had no significant effect on that of mercury. The effects of selenium IP on these organisms were markedly different. P. lutheri, growing in media containing selenium IV above threshold concentrations, recovered completely after several days, but this metal, at similar concentrations, caused complete cell destruction of D. minute. Although mercury and selenium both inhibited the growth of D. minute when added to a culture separately, when present together they displayed an antagonistic rather than a synergistic effect. Prior exposure of the culture to either metal for 2 days did not alter their combined effect. Similar antagonism was observed for combinations of selenium and copper. The effects of mercury on cell population, chlorophyll a concentration and rates of photosynthesis and excretion were also investigated in D. minute. Chlorophyll a concentration and cell numbers were affected in a similar manner, whereas the photosynthetic rate was inhibited to a significantly lesser degree. The excretory rate was markedly increased at concentrations 250 ppb of mercury, but at lower concentrations it tended to depend more on the physiological state of cells than on mercury concentration. In all the cultures the photosynthetic activity showed large variations over the period of growth; these occurred without major changes-in the chlorophyll content per cell. An attempt is made to relate these observations to probable physioochemical and biological changes oocurring in the medium during growth and to the metabolism of the organisms. Possible ecological consequences are discussed.

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