Many nanotoxicological studies have assessed the acute toxicity of nanoparticles (NPs) at high exposure concentrations. There is a gap in understanding NP chronic environmental effects at lower exposure concentrations. This study reports life-cycle chronic toxicity of sublethal exposures of polyvinylpyrrolidone-coated silver nanoparticles (PVP-AgNPs) relative to dissolved silver nitrate (AgNO3) for the estuarine meiobenthic copepod, Amphiascus tenuiremis, over a range of environmentally relevant concentrations, i.e., 20, 30, 45, and 75 µg-Ag L−1. A concentration-dependent increase in mortality of larval nauplii and juvenile copepodites was observed. In both treatment types, significantly higher mortality was observed at 45 and 75 µg-Ag L−1 than in controls. In AgNO3 exposures, fecundity declined sharply (1.8–7 fold) from 30 to 75 µg Ag L−1. In contrast, fecundity was not affected by PVP-AgNPs exposures. A Leslie matrix population-growth model predicted sharply 60–86% of decline in overall population sizes and individual life-stage numbers from 30–75 µg-Ag L−1 as dissolved AgNO3. In contrast, no population growth suppressions were predicted for any PVP-AgNPs exposures. Slower release of dissolved Ag from PVP-AgNPs and/or reduced Ag uptake in the nanoform may explain these sharp contrasts in copepod response.