Animals in the sea absorb, scatter, reflect, emit and sense underwater light. Large well developed eyes in most long range marine migrators suggest its navigational importance. Submarine light polarization may provide species that perceive it with a kind of sun compass even in deep water. Laboratory evidence has been found for compass card-like orientation to e-vector direction by both fishes and crustaceans.© (1988) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.