IMPACT OF PLANKTIVOROUS FISHES ON DISPERSAL, HATCHING, AND MORPHOLOGY OF ESTUARINE CRAB LARVAE

In the upper Newport River estuary, North Carolina, >99.6% of the plankters collected were decapod larvae, copepods, barnacle nauplii, and cyprids. Predominant fishes in the upper estuary were silversides Menidia menidia, anchovies Anchoa mitchelli and killifish Fundulus heteroclitus. Silversides and anchovies preyed upon crab larvae more often than did killifish, and are most likely to influence the life history patterns of crabs inhabiting upper estuaries. Fishes that eat crab larvae are more abundant in estuaries than coastal waters during summer. Fishes in the estuary and the laboratory showed strikingly similar preferences for prey. In order to descending preferences, natural populations of fishes preferred copepods, crab larvae that are exported from estuaries (Uca, Sesarma cinereum), and decapod larvae that develop in estuaries (Sesarma reticulatum, Palaemonetes, Rhithropanopeus harrisii). In the laboratory, juvenile and adult silverside and killifish preferred Artemia nauplii to crab larvae, they fed randomly on Uca larvae, and they avoided R. harrisii larvae. Predation generally was greatest upstream in shallow, narrow areas of the upper estuary on diurnal neap tides. Estuarine crabs may have responded to predictable trends in planktivory by dispersing newly hatched zoeae downstream on nocturnal ebb tides, regardless of where larvae develop. Small vulnerable zoeae eventually disperse offshore, whereas large well-defended zoeae apparently remain in estuaries. -from Author