Effects of cadmium on a microbial food chain, Chlamydomonas reinhardii and Tetrahymena vorax.

A steady-state microbial food chain consisting of the green alga Chlamydomonas reinhardii and the ciliated protozoan Tetrahymena vorax was established in a two-stage, nitrogen-limited chemostat. The lowest concentration of cadmium which produced a toxic effect at the population level was between 7.5 and 10 micrograms l-1. The algal population acclimated to the presence of cadmium up to 40 micrograms l-1 added in increments over time, but demonstrated lowered cell numbers and reduced cell weights. Protozoan populations acclimated to 40 micrograms Cd l-1 added incrementally if the rate of dilution was lowered. Abrupt elevation of the cadmium concentration to 40 micrograms l-1 resulted in extreme fluctuations in the specific growth rates of both populations and the incipient loss of all cells from the system (washout).