Paul Galtsoff studied oysters, sponges, and other marine life at sites scattered around the Atlantic and Pacific Oceans. He was an expert in virtually every aspect of oyster biology: physiology, histology, morphology, life cycle, behavior, diseases.

He wrote the definitive book on the American oyster and compiled a bibliography of oyster publications that contained more than 17,500 references and weighed 9 pounds. Galtsoff was also an able administrator, directing the Woods Hole fisheries laboratory for most of the 1930s and 40s and keeping it functioning when it was in danger of being closed and sold as surplus government property.