He was the first to describe communities of benthic marine invertebrates and is often considered a founder of modern fisheries research.
Petersen studied natural history at the University of Copenhagen under professor Japetus Steenstrup.
He participated in expeditions 1883-1886 and sampled the benthic fauna in Danish waters systematically.
In 1889, he co-founded Dansk biologisk Station, which was a mobile laboratory in a former naval transport vessel that was put in a new location every spring and anchored for the summer.
Nevertheless, today he is mainly remembered for his significant contribution to the development of the community concept for marine benthos.