Resistance to zinc ofStigeoclonium tenuein the field and the laboratory

Abstract

Field and laboratory studies were carried out on the tolerance to Zn of S. tenue growing in flowing waters. Thirty-four different sites in England, France and Germany were included, the majority of them being chosen to represent examples of Zn pollution resulting from past or present mining activities. S. tenue was sometimes abundant in Zn polluted waters, and was found at sites with up to 20.0 mg l-1 of Zn capable of passing through a filter. At sites with field mean Zn levels of about 0.2 mg l-1 and above, populations show increased resistance to Zn in comparison with populations from sites with lower Zn levels, this increased resistance being largely, if not entirely, the result of genetic adaptation. Assays of populations from sites with high Ca levels suggest that these are less tolerant of a particular level of Zn than are populations from sites with low Ca levels. Levels of Zn bringing about a marked reduction in total growth during assay have a relatively greater effect on the erect part of the thallus than on the basal system. In the field S. tenue was restricted to a basal growth form only at the site with the highest level of Zn.