The effects of chronic cadmium stress on energy acquisition and allocation in a freshwater benthic invertebrate predator

Abstract

The effects of chronic exposure to cadmium (0 (control), 5 (low), 10 (medium), or 50 (high) μg Cd 1 −1) were examined in terms of changes in energy acquisition and allocation (somatic growth, reproductive growth, faeces plus mucus, active respiration, resting respiration, activity time) in the predatory leech Nephelopsis obscura. Leeches in the high Cd treatment had significantly lower biomass production, survivorship and ingestion rate than leeches in the other treatments or control. Assimilation efficiency, reproductive investment, resting respiration and active respiration were unaffected by Cd but leeches in the high Cd treatment were significantly less active and produced more mucus. Decreased ingestion and increased mucus production in the high Cd treatment contributed to a lower growth rate. Although Cd had no significant effects on resting or active respiration, there were significant effects on total respiration as leeches exposed to high Cd exhibited a significant decrease in time spent active and thus in total respiration. Significant mortality in the high Cd treatment indicates that leeches are unable to compensate. As reproductive investment did not change with Cd exposure, the only physiological tradeoffs occurred between growth of somatic tissue and survival mechanisms.