Use of life tables and lc50 tests to evaluate chronic and acute toxicity effects of copper on the marine copepod tisbe furcata (baird)

Abstract

AbstractCohorts of the epiphytic marine copepod Tisbe furcata were chronically exposed to copper in life‐table experiments to test whether ecologically relevant impacts can occur at sublethal concentrations. Data on fecundity, longevity, and rate of development were used to calculate rm – the intrinsic rate of natural increase. Acute toxicity tests (96‐h LC50 tests) were done to compare the concentrations of copper affecting individual lethality and population biology. The LC50 value for Tisbe furcata nauplii was 2.8 μM copper (178 μg/L). The results from the life‐table experiments show that 0.9 μM copper (32% of LC50) can cause significant negative effects on demographic parameters (total production of nauplii, life span, and reproductive period for fertile females) and reduce the percentage of fertile females leading to a 61% reduction of rm. However, rm was still positive at 0.9 μM copper, and the net reproductive rate (Ro) indicated a fivefold increase in population size from one generation to the next. Although there were no significant effects of copper at 0.5 μM (18% of LC50), there was a negative trend in almost all the demographic parameters, indicating that the observed 10% reduction of rm at this concentration was an effect of copper. For the substances tested so far with both acute LC50 tests and life‐table experiments, rm was not reduced at concentrations below LC50/10. When life‐table experiments are used as part of environmental hazard assessments, concentrations below LC50/10 should be tested to detect substances that are potentially harmful to the environment at sublethal concentrations, rather than testing concentrations close to LC50.