Settlement of blue crab Callinectes sapidus megalopae in a North Carolina estuary

Nightly settlement of blue crab Callinectes sapidus megalopae on passive collectors was monitored from September to November over 7 yr at a single location in the Newport River estuary (North Carolina, USA). The total number of megalopae settling varied yearly from 1869 to 12007. Megalopal abundance was generally related to commercial landings of adult crabs 2 yr later. Throughout the sampling period, megalopae settled continuously at low levels with episodic peaks. The 6 largest peaks accounted for > 50% of all settlement in most years. Settlement was not related to along- or across-shore wind stress, but time-series analysis indicated significant periodicity in settlement in all years. In 4 of the years there was a semi-lunar periodicity with settlement occurring at the time of neap tides during the quarter phases of the moon. Detailed analysis of settlement peaks from all years also indicated a relationship to neap tide. The proposed explanation for this relationship is that (1) megalopae undergo flood-tide transport for entrance into estuaries and up-estuary movement, and (2) the behavior underlying flood-tide transport is most effective when all of the nocturnal flood tide occurs in darkness. The latter situation occurred during neap tides at the quarter phases of the moon when the average time of slack water at the end of flood tide occurred after midnight.

Duke Scholars

Author Richard B. Forward Marine Science and Conservation