Life-table evaluation of sediment-associated chlorpyrifos chronic toxicity to the benthic copepod, Amphiascus tenuiremis

A partial life-cycle experiment was conducted to assess chronic effects of sediment-associated chlorpyrifos, an organophosphate pesticide, on a marine, benthic copepod population. The static-renewal experiment was initiated with 4 treatments including control, 13 replicates per treatment with one female (bearing first clutch of eggs) per replicate. No males were added because one fertilization is sufficient for several clutches. Once weekly, all replicate chamber contents (10-ml culture tubes with 1.5 mi of sediment and 5 mi of seawater) were sieved and enumerated to determine survival and fecundity. Surviving adult females were placed back into chambers with newly spiked sediments. This process was repeated for 7 weeks until all initial females were dead or reproduction had ceased for at least two weeks. Survival and fecundity data were then used to determine population dynamic parameters such as r (intrinsic rate of natural increase) for each treatment. Results revealed a chronic toxicity response with significant population effects (p < 0.05) in all pesticide treatments versus the control; concentrations that represent 7-32% of the 96-hr LC(50). The control treatment had an r value 26-52% higher than the pesticide treatments. This translated into a control population rate increase of up to twice that of pesticide treatments. In addition, significant reductions in weekly and total fecundity were found in all chlorpyrifos treatments. Based on these results, usage of population parameters with benthic copepods allows for an integrative measurement of population effects from chronic exposure to sediment-associated contaminants.