Obtaining a census of marine life is important to understanding changes in marine ecosystems that result from stressors such as overfishing, ocean acidification, hypoxia, pollution and biological invasions. Traditional monitoring depends on individuals who count marine populations. It is invasive, expensive time-consuming and error-prone. This project proposes to measure marine populations more efficiently by sequencing environmental DNA (eDNA) in water samples that is, evaluating tissue cells and waste shed by marine life to measure the distribution, diversity and abundance of the organisms present. It would fulfill an urgent need for accurate and efficient marine animal monitoring tools. It would be especially useful for identifying the presence of endangered animals, migrating animals, marine mammals or invasive species.