TIMING OF LARVAL PRODUCTION AND FLUX OF INVERTEBRATE LARVAE IN A WELL-MIXED ESTUARY

Abstract

Flux of invertebrate larvae between an estuary and coastal waters and the effect of the timing of larval production by estuarine crabs on larval transport were studied in North Inlet estuary, South Carolina. Invertebrate larvae were sampled from three transects across the entrances to this well-mixed estuary during spring and neap tidal periods in each season in 1979. Crab zoeae also were sampled nightly throughout the summer at a single station in the upper reaches of the estuary. The net flux of most larval groups corresponded to the net flux of water and was not different from zero. Six of the 20 larval groups sampled (e.g. echinoderm plutei, barnacle cyprids) showed significant imports to the estuary during one or more sampling periods. Only crab zoeae were exported significantly from the estuary. Such exports occurred during spring tidal periods in the summer when the densities of stage I zoeae of the seven dominant estuarine species were 6 to 57 times greater in the lower estuary and 100 to 10,000 times greater in the upper estuary than during neap tidal periods. Maximum zoeal densities occurred when female crabs released larvae. The timing of larval release may result in rapid seaward transport of newly hatched zoeae on nocturnal ebb tides of greatest amplitude during the semilunar cycle, leading to significant net export from the estuary.