ABSTRACT: Topographical features like depressions and submarine canyons accumulate organic debris that fuel patches of intense secondary production. A submarine canyon system off the coast of La Jolla, California, USA, harbors an assemblage of leptostracan andamphipod crustaceans whose local density and secondary production greatly exceed those of any natural system yet reported. These crustaceans utilize large accumulations of macrophyte detritus as both habitat and food, and are preyed on by numerous speciesof fishes. Bottom topographies acting as detritus traps are relatively common along many coasts and provide an important mechanism to channel marine macrophyte production into higher trophic levels.