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

Abstract

A total of 75 weekly exploited populations of the harpacticoid copepodTisbe holothuriae Humes were exposed to 0.06, 0.3, 1.5, 7.5 or 37.5 μg 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. An unusually high mortality was observed for some weeks which could not be ascribed to the added amounts of Cd⁺⁺. A change in properties of supplied water is considered responsible for the unintentional perturbation which offered a further opportunity to study the effect of compensating reactions in stress situations. The results obtained clearly indicate an effect of exploitation rate on responses to detrimental influences. A superior performance has been found in populations exploited at higher rates. The findings are discussed with respect to earlier investigations on the population dynamics ofT. holothuriae.