On the dynamics of exploited populations ofTisbe holothuriae (Copepoda,Harpacticoida)

A total of 30 weekly exploited populations of the harpacticoid copepodTisbe holothuriae Humes were exposed to 148 or 222µg Cd⁺⁺ l^–1, combined with exploitation rates of 10, 30, 50, 70 or 90% under conditions of surplus food supply at 22 °C and 30 S. During the observation period, most populations exhibited distinct U-shaped density trends. Addition of Cd⁺⁺ prolonged and reinforced the downward trends present in the initial periods of the experiments. If population densities, both in control and test populations, fell short of a certain value, the age structures shifted in favour of the nauplii. More pronounced reductions in population densities of the test populations did not result in increased elevations of the nauplius fraction. Within 23 weeks (or 20 generations), the effect of Cd⁺⁺ on population density was counteracted by an acclimation process. No relationship could be established between exploitation rate and observed effects. Erroneous assumptions on the adaptability of parametric methods had led to invalid statements on the dispersion of data published in previous papers of this series. These statements have been revised. Possible limitations of the significance of the results obtained are discussed in some detail.