This dataset includes measurments of stable carbon, nitrogen isotopes in tissues of eight epibenthic suspension feeders and Macrocystis pyrifera (giant kelp) at three reefs in the Santa Barbara Channel during 2010 and 2011, as part of a study to (a) determine the contributions of phytoplankton and giant kelp detritus to the pool of suspended reef particulate organic matter (POM), and usage by benthic susupension feeders and (b) whether POM composition varies with distance from kelp forests. Species sampled include Chaceia ovoidea (bivalve), Aglaophenia spp (ostrich plume hydrozoan), Cucumaria piperata (echinoderm), Muricea californica (cnidarian), Phragmatopoma californica (tube worm), Parapholas californica (bivalve), Pachythyone rubra (echinoderm), and Styela montereyensis (tunicate). Samples were collected at three core SBC LTER research reefs: Arroyo Quemado, Arroyo Burro, and Mohawk. Potentially important food sources to benthic suspension-feeders on shallow subtidal reefs include phytoplankton-dominated seston, kelp-derived detritus, and for locations adjacent to sources of freshwater runoff, terrestrially-derived material. Our data will be input to mixing models to estimate the contribution of each source to the reef food web.