Net ecosystem production (NEP) refers to balance between primary production and community respiration and is one measure of the potential of the carbon mitigation ecosystem service provided by kelp forest communities. We used respirometry chambers to assess NEP of restored kelp (Ecklonia radiata) patches on artificial reefs seeded with four densities of kelp (zero (0), low (4), natural (8), and high (16 kelp m-2)). While gross primary production (GPP) was highest on reefs supporting kelp at natural and high densities, community respiration exceeded GPP across all kelp densities, highlighting the net heterotrophic (net CO2 source) nature of these systems. Ultimately however, carbon mitigation services should be assessed relative to the alternative ecosystem state (e.g. restored vs. non-restored, kelp vs. turf). As the high-kelp-density reefs yielded greater (i.e. less negative) NEP values as a result of lower CO2 production than the turf algae communities that developed on reefs without kelp, restoring dense kelp cover in place of degraded turfs represents a net carbon mitigation service. Irrespective of the carbon balance of kelp forest communities, kelps should remain highly valued for the suite of other ecosystem services they provide, including their high absolute levels of primary and secondary production and their contribution to supporting the rich biodiversity of temperate reef systems.