Mortality, Preference, Avoidance, and Activity of a Predatory Leech Exposed to Cadmium

Abstract.

The effects of cadmium on the hatching success of the cocoons of the freshwater predatory leech Nephelopsis obscura were examined together with the survivorship of hatchlings, changes in 96-h LC₅₀ with biomass, preference-avoidance responses and changes in activity. The 96-h EC₅₀ for cocoons was 832.6 μg Cd/L with a decreasing bounded monotonic function best describing hatchling success as a function of Cd concentration. Exposure of cocoons to Cd had a highly significant effect on post-hatchling survivorship with survivorship of hatchlings from the 0–500-μg Cd/L concentrations not significantly different from each other but higher than survivorship of hatchlings from cocoons exposed to 1,000–4,000 μg Cd/L. Resistance to acute Cd toxicity, measured as LC₅₀, increased with leech biomass. In preference-avoidance tests large leeches (>450 mg) spent more time in 100- and 200-μg Cd/L than in control water or in 50-μg Cd/L, while small leeches (<250 mg) spent more time in 200-μg Cd/L compared to control water or 50–100-μg Cd/L. Leeches exposed to 100- and 200-μg Cd/L exhibited a significant decrease in activity compared to the leeches in the control and 50-μg Cd/L treatments.