On the selection for heavy metal tolerance in diatoms from the derwent estuary, tasmania

To assess the metal tolerance of phytoplankton from the polluted Derwent estuary in Tasmania, unialgal clonal cultures of three marine diatoms were established from recent isolates. Skeletonema costatum, Melosira moniliformis, and Gyrosigma sp, were exposed to varying levels of copper and zinc and metal uptake and growth response were monitored. Cells of S. costatum, the only species for which direct comparisons were possible, appeared to have greater zinc, but not copper, tolerance than had S. costatum cells isolated from cleaner waters. Unlike the other species, Gyrosigma sp. responded to zinc stress with an extended lag phase, followed by apparent recovery. Uptake of copper and zinc by these species did not significantly differ from that of more sensitive cells. In the Derwent water from which the cells were isolated, the total dissolved copper concentration was 1763 nM, with only 69 nM being polarographically labile, while 84% of the total dissolved zinc (concn 1805 nM) was labile. It appears that it is the labile metal, rather than total metal, which provides selection pressure for metal tolerance, presumably because only this fraction is available for algal uptake.