A series of experiments was designed to reveal the trophic structure of a benthic community using kelp holdfasts as microcosms within the kelp-bed community. The experimental food comprised zooplankton represented by 3H,0-labelled Arternia sp. eggs and nauplii (200 to 300 pm), detritus derived from "C-labelled kelp (60 to 90 pm), and phytoplankton represented by 14C-labelled Dunaliella primolecta (5 to 10 pm) cultures. Separate experiments of short duration (1 to 2 h) were used to indicate the primary consumers on each type of food, while longer experiments (4, 8 and 16 h) suggested the secondary consumers (coprophagous and carnivorous species). Several species were found to be omnivorous.