Due to their broad-spectrum antimicrobial action and ease of synthesis, silver nanoparticles (AgNPs) are one of the most widely used nanomaterials in different industrial and ecological areas. AgNPs are released into marine ecosystems; however, their ecotoxicological effects have been overlooked. In this study, we evaluated the toxic effects of biogenic and synthesized AgNPs on sea urchin Echinometra lucunter embryos and compared them to those of AgNO3. Fertilized eggs were exposed to five concentrations of the test compounds and a negative control for 48 h under controlled conditions. The EC50-48h of biogenic and synthetic AgNPs and AgNO3 were 0.31, 4.095, and 0.01 ug L-1, evidencing that AgNPs are less toxic than AgNO3, and that synthetic AgNP is less toxic. Toxicity to E. lucunter embryos could be explained by the fact that Ag affects DNA replication and induces the formation of pores in the cellular wall, leading to apoptosis.