15 Oct 1953) is an Irish-born American marine scientist and comparative physiologist.
He is known for Antarctic and deep oceanic research on the physiology and ecology of marine invertebrates and their larvae in extreme environments, and for his interest in the role of dissolved organic material as a larval food source.
From 1980 to 1983, he was a post-doctoral fellow in the laboratory of Grover C. Stephens at the University of California at Irvine.
Manahan joined faculty at the University of Southern California in 1983.
Manahan Peak in Antarctica was named in honor of his contributions to research and education on that continent.