Different demographic responses of the polychaete Dinophilus gyrociliatus to metal exposure.

The purpose of this study was to investigate in comparison the sensitivity of some populationparameters such as the population growth rate l, the life expectancy e0 and the net reproduction rate R0estimated for cohorts of Dynophilus gyrociliatus exposed to different heavy metals. Comparison of thesurvival, fecundity and demographic indices of a laboratory culture of D. gyrociliatus between two treatedcohorts kept in artificial seawater enriched with nominal concentrations of 1.00 mg Zn/ml added as ZnCl2 and1.00 mg Cr/ml added as Cr Cl3 respectively, and two control groups was performed. The net growth rate, R0,appeared the demographic parameter most sensitive to metal enrichment: in fact both zinc and trivalentchromium determined a sharp decline of R0 with respect to controls. To a lesser extend life expectancy, e0,was also reduced by zinc and chromium, while metal enrichment did not affect the population growth rate, l.Although l is often used as index of population fitness, the variations of R0 due to pollutants should not beunderestimated from a population biology perspective. Considering all demographic effects of a toxicant ontarget organisms would appear to be a precautionary means to ensure the maintenance of wild populations.