Stephen has been associated with the Coastal Resources Center since its creation in 1971, and has served as its director since 1975. From 1985 - 2003, Stephen was the international director of the Coastal Resources Management Program sponsored by the U.S. Agency for International Development. That program is widely recognized as a pioneer in developing a learning-based, issue-driven approach to the management of coastal ecosystems through long-term programs in Latin America, East Africa and Southeast Asia. He has worked with the World Bank, the Inter-American Development Bank and the United Nations Development Program on their coastal management initiatives. Stephen is regarded as one of the leading authorities worldwide on coastal governance.

Stephen is a member of the Committee on International Capacity Building for the Protection and Sustainable Use of Oceans and Coasts sponsored by the National Academy of Sciences.

He is also a member of Scientific Steering Committee of the Land Ocean Interactions In the Coastal Zone (LOICZ) Program. This is one of the global programs sponsored by the International Geosphere Biosphere Program. He leads the working group on the governance dimensions of ecosystem change in coastal regions.

He is an Affiliated Professor of Oceanography at the University of Rhode Island (URI).