Numerical abundance, biomass, and caloric content of zooplankton were estimated from biweekly samples collected during 1970–1972 from the lower estuary of the Newport River, North Carolina. All three measurements generally were maximum during early fall and again in late winter or early spring. During November larval fishes, primarily pinfish (Lagodon rhomboides), spot (Leiostomus xanthurus), and menhaden (Brevoortia tyrannus), began entering the estuary. The larvae reached maximum abundance in the estuary during March and April. Zooplankton abundance declined significantly at this time during 1970 and somewhat later during 1971. We hypothesize that zooplankton abundance may control the survival of fishes during their transition from larvae to juveniles and that the larvae have a significant effect in reducing the standing crop of zooplankton. Analysis of the gut contents of these fishes indicated they feed predominantly on zooplankton. Routine metabolism of the larvae would require that the standing crop of larvae graze an average 10 percent of the 1970 standing crop of zooplankton daily during January–May.