Effects of 4-n-nonylphenol on life-history traits and population dynamics of a polychaete

A Life-Table-Response Experiment lasting 78 d was performed to investigate the toxic effects of sediment-associated 4-n-nonylphenol (NP) on growth, re production, and survivorship of isolated hermaphrodites of the infaunal pol ychaete Capitella sp. I. Demographic effects were evaluated using both a fu lly age-classified and a simple two-stage model to estimate population grow th rates (lambda). Decomposition analysis was performed to explore the cont ributions of each of the affected life-history traits to the effects observ ed on lambda. Elasticity analysis was applied to examine the relative sensi tivity of lambda to changes in each of the different life-history traits un der different exposure levels. In the lowest NP treatment (14 mu g NP/g dry mass of sediment) significant stimulatory effects were observed for both asymptotic body volume and avera ge brood size, but these did not result in a significant effect on lambda. Negative effects on brood size, volume-specific fecundity, time to first re production, and individual growth rate were significant in the highest NP t reatment (174 mu g/g dry mass), and these effects resulted in a significant reduction in lambda. Decomposition of the two-stage model indicated that t he effect of NP on time to first reproduction was a major cause of changes in population growth rate. Although time to first reproduction increased by only similar to 20% in the highest NP treatment relative to the control, i t was responsible for more than half (55%) of the effect on lambda. In cont rast, per-individual fecundity decreased by 75% but only explained 44% of t he effect on lambda. Elasticity analysis of the two-stage model showed that lambda became less sensitive to changes in fecundity and time to maturity, but not to changes in juvenile and adult survival probabilities, with incr easing NP exposure. In this study, population growth rate was not significantly affected by NP concentrations lower than those affecting the individual life-history trait s. However, since the population-level consequences of changes in each trai t depend on the starting value of lambda, on the extent to which the other traits are impacted by the toxicant, and on the life-history characteristic s of the species under consideration, the application of demographic analys es to chronic toxicity test results is required to link individual-level re sponses to population-level impacts of toxicant exposure.