Figure 1.

Activity as a measure of survival in four species of tardigrades following 24 h exposure to copper. (A) Activity in proportions (mean ± s.e.m.) of each of the four tardigrade species under control conditions (n = 9 groups of ~20 Echiniscoides sigismundi and n = 6 groups of ~20 tardigrades for the other species). (B–E) Tardigrade activity 24 h after removal from copper solutions as a function of copper-concentration. Each data-point represents the activity in proportions in a group of ~20 tardigrades exposed to a given measured copper concentration. EC50 values (95% confidence intervals in parentheses) for E. sigismundi (B) and, Ramazzottius oberhaeuseri (D) were estimated using a dose-response fit. Fits (not shown) for Echiniscus testudo (C) and Halobiotus crispae (E) had low r² values due to increased activity rates recorded following exposure to high copper concentrations. (F) Activity of H. crispae over a period of 10 days following 24 h exposures to copper. Each data-point represents the activity in proportions at a given time for nine groups of ~20 tardigrades exposed to measured copper concentrations of, respectively, 379, 400, 445, 453, 483, 490, 569, 572, and 574 μg l⁻¹. For simplicity the 6 groups exposed to the lowest concentrations have been marked by (), whereas the three groups exposed to the highest concentrations were marked (). Activity at t = 1 day represents the activity of tardigrades immediately following removal from the respective copper-solutions. Three control groups (■) were kept in Vellerup Vig sea water (6 μg Cu l⁻¹) for the entire period.