Effect of 3,4-dichloroaniline and metavanadate on Daphnia populations.

Fourteen continuously fed populations of Daphnia magna were exposed to 3,4-dichloroaniline (3,4-DCA) or metavanadate and monitored for 20 (two controls), 14 (six with metavanadate), and 8 (six with 3,4-DCA) weeks. The controls showed a damped oscillation. Low concentrations of either 3,4-DCA or metavanadate stimulated the first population peak. High concentrations of metavanadate rendered population peaks less regular, and at the highest metavanadate concentration, one population perished. High concentrations of 3,4-DCA slightly reduced population size. Four periodically fed populations of D. magna were also monitored. The more they were fed, the larger they grew. In the continuously fed populations, ephippia were formed at and just after the population peaks. No ephippia were noted in the periodically fed populations. Metavanadate promoted the formation of ephippia (NOEC 0.56 mg/liter), and 3,4-DCA depressed sexual reproduction at all concentrations tested (6, 12, and 24 micrograms/liter). The population dynamics of the controls were compared with those predicted by Kooijman's model (1986a, in The Dynamics of Physiologically Structured Populations (J.A.J. Metz and O. Diekmann, Eds.), pp. 266-297, Springer Lecture Notes in Biomathematics; 1986b, J. Math. Biol. 23, 163-185) for growth and reproduction of individual daphnids. In general, there is reasonable agreement between model predictions and observations, but some adjustments to the model may be necessary.