EFFECTS OF NICKEL ON DAPHNIA-MAGNA DURING CHRONIC EXPOSURE AND ALTERATIONS IN THE TOXICITY TO GENERATIONS PREEXPOSED TO NICKEL

Daphnia magna was cultured at sublethal nickel concentrations. The mean life expectancy was significantly less when exposed to ≥40 ppb Ni. Statistically significant reductions of the number of offspring, maximum body length of adults and of neonates were caused by ≥80 ppb Ni. The length and brood size of primiparous animals were significantly less when exposed to ≥120 ppb Ni. The intrinsic rate of population growth (r) was inversely proportional to nickel concentrations. During seven successive generations exposed to 160 ppb Ni, both the mean life span and the length of primiparous animals decreased significantly with increasing time. The progeny of nickel pre-exposed generations exhibited no adaptation towards nickel except an altered reproduction pattern which induced an increase of r. After the transfer into nickel-free water, the progeny of nickel pre-exposed generations showed an increase of body length, mean life span, number of offspring, brood size and brood number as well as the maximum body length of neonates. However, the progeny of pre-exposed generations remained smaller than the progeny of an untreated generation. © 1990.