Projecting Population-Level Response of Purple Sea Urchins to Lead Contamination for an Estuarine Ecological Risk Assessment

As part of an ecological risk assessment case study at the Portsmouth Naval Shipyard (PNS), Kittery, Maine, USA, the population level effects of lead exposure to purple sea urchin, Arbacia punctulata, were investigated using a stage-classified matrix population model. The model divided the life history of A. punctulata into five classes, incorporating both, the developmental stages of this species and the endpoints from a laboratory bioassay. Finite population growth rate ( lambda ) was the metric relating population level impact to lead exposure. An inverse relationship was observed between lead tissue residues in A. punctulata and lambda . Bioassay treatments which resulted in significant impacts on fertilization success and zygote viability did not translate into significant effects on lambda , unless those treatments also negatively impacted adult survival. These results paralleled the elasticity (relative sensitivity) analysis of the model, which indicated that lambda was most sensitive to adult and subadult survival and was relatively insensitive to fecundity, fertilization success, or zygote survival. Model results indicated that the environmental lead levels observed at PNS should not pose significant ecological risk to sea urchin populations. Additionally, the model results indicated that impacts to the early life stages routinely used in toxicity testing do not necessarily translate directly into impacts at the population level.