Seagrasses are an important refuge for fishes and provide ecosystem services worldwide. Along the Pacific Coast, however, quantitative assessments of the ecological role of seagrass habitats with limited anthropogenic impacts are lacking despite their value to resource management. To address these issues, the ecological function of the eelgrass Zostera marina Linnaeus in a protected area off Santa Catalina Island, California, USA was quantified using estimates of secondary production in the kelp bass Paralabrax clathratus (Girard 1854). Monthly assessments of eelgrass structural complexity, as well as the size and abundance of juvenile kelp bass were used to establish a baseline of fish biomass and recruitment associated with Zostera habitat. The greatest number of kelp bass was recorded in the summer and fall months and the fewest during the winter and spring. Secondary production in kelp bass (0.1 to 0.59 g m<sup>−2</sup> mo<sup>−1</sup>) followed monthly changes in Zostera habitat structure throughout the 24-month study period. Seasonal changes in the structural complexity of coastal eelgrass beds may influence the flow of energy to adjacent reef environments through the transfer of fish biomass. These findings will help to define the role of Zostera habitat within the larger context of nearshore coastal ecosystems in the Southern California Bight.