We compared food availability of filter-feeding bivalves, Anadara spp., between two Fijian sites of different mangrove richness to evaluate impacts of environmental variables on Anadara spp. abundance and body size. Suspended particles including planktonic organisms and detritus were more abundant in the fishery grounds of the mangrove-rich site (MR) than in the mangrove-poor site (MP). Athough no substantial difference was observed in abundance of Anadara spp., dry weights of soft tissue were heavier for animals at MR than those at MP. Respiration rates (i.e., minimum metabolic requirements) of Anadara spp. decreased with increasing animal weight. Unicellular planktonic biomass was estimated to support the Anadara community metabolic requirements (i.e., minimum food requirement) for 9.2 to 85.7 days at MR and 1.4 to 67.4 days at MP, indicating that the planktonic biomass cannot support sufficient growth of the bivalve population at some locations. These results suggest that suspended particles support increased shell sizes of Anadara spp. and that resuspended detritus is a supplement or alternative food resource for these bivalves in mangrovecoral associated ecosystems.