Endogenous swimming rhythms of blue crab, Callinectes sapidus, megalopae: Effects of offshore and estuarine cues

Published

Journal Article

Larvae of the blue crab Callinectes sapidus Rathbun develop on the continental shelf. The postlarval stage (megalopa) occurs near the surface and is transported shoreward by wind-driven surface currents. It then uses selective tidal stream transport for migration up an estuary. Endogenous swimming rhythms were measured under constant dark conditions in the laboratory in megalopae collected from the Newport River Estuary (North Carolina), the Delaware Bay, and offshore from the Newport River Estuary. Megalopae from all areas had a similar circadian activity rhythm, in which they swam during the time of the day phase in the field and were inactive at night. This rhythm predicts the presence of a reverse, diel, vertical-migration pattern offshore which would contribute to the location of megalopae near the surface during the day. The rhythm lacks obvious ecological significance in estuaries because it does not contribute to selective tidal stream transport and would increase vulnerability to visual predators during the day. Attempts to entrain a circatidal rhythm in swimming by cyclic and step changes in salinity were unsuccessful, as the circadian rhythm persisted. The rhythm also continued in the presence of the eelgrass Zostera marina, which is a site of settlement and metamorphosis in the field. Thus, megalopae enter estuaries with a solar day rhythm in activity. This rhythm, however, is not expressed, because light inhibits swimming during the day upon exposure to estuarine water. Since this light inhibition is removed in offshore waters, the rhythm would be expressed if, after entering an estuary, megalopae were transported back to offshore areas.

Full Text

Duke Authors

Cited Authors

  • Forward, RB; Swanson, J; Tankersely, RA; Welch, JM

Published Date

  • March 1, 1997

Published In

Volume / Issue

  • 127 / 4

Start / End Page

  • 621 - 628

International Standard Serial Number (ISSN)

  • 0025-3162

Digital Object Identifier (DOI)

  • 10.1007/s002270050052

Citation Source

  • Scopus