Numerous primary producers may contribute to the diet of saltmarsh consumers despite the historical assumption that Spartina spp. detritus is the basis of estuarine food webs. To address the relative dietary contribution of primary producers to saltmarsh food webs in the Plum Island Estuary, Massachusetts, we conducted multiple studies using natural abundance stable isotopes (d¹³C, d¹⁵N and d³⁴S) and enriched stable isotope additions (¹³C and ¹⁵N). An array of consumers over multiple trophic levels, with various feeding modes were analyzed over space and time including deposit feeding annelids (i.e. Streblospio benedicti, Manayunkia aestuarina and Paranais litoralis), the amphipod Orchestia grillus, the ribbed mussel Geukensia demissa, the killifish Fundulus heteroclitus and the grass shrimp Palaemonetes pugio. In general, we found most organisms consumed only small amounts of Spartina spp. detritus. Instead, benthic and pelagic algae appeared to be the dominant contributors to the diet of saltmarsh consumers regardless of feeding mode, habitat or time of year. Our work is in agreement with others who have departed from the idea that Spartina spp. detritus serves as the base of saltmarsh food webs.