Anders Sandøe Ørsted (1816-1872) was a pioneering Danish marine biologist who made significant contributions to the field of marine ecology. His treatise De Regionibus Marinis from 1844 is the first published book on marine ecology. Ørsted's epoch-making work laid the foundation for future marine research, and his insights into the dynamics of marine food chains had a profound impact on our understanding of oceanic life. Now, Ørsted's work has been translated from Latin into English for the first time.