THE CIRCATIDAL RHYTHM IN VERTICAL SWIMMING OF FEMALE BLUE CRABS, CALLINECTES SAPIDUS, DURING THEIR SPAWNING MIGRATION: A RECONSIDERATION

Abstract

Ovigerous blue crabs, Callinectes sapidus Rathbun, undergo ebb-tide transport (ETT) during the spawning migration from estuaries to coastal areas where they release larvae. An initial field study found that only females with mature embryos underwent the spawning migration and that postspawned females switched to flood-tide transport for movement back into and up estuaries. Alternatively, a more recent field study found ETT occurred in females throughout embryo development and continued after larval release. An endogenous rhythm in vertical migration underlies ETT during the spawning migration. A past study found the circatidal rhythm was only present in females with mature embryos but not in females with immature embryos or after larval release. The present study reinvestigates this rhythm in vertical migration. Both females with early embryos and postlarval release females entrained in the field have circatidal rhythms, in which they swim vertically at the time of consecutive ebb tides at the collection site or on alternate ebb tides. These results support the field study that ovigerous females undergo ETT throughout embryo development and after larval release. Thus, females will be transported seaward and release subsequent larval clutches in coastal areas that increase the likelihood that larvae will be transported to offshore developmental areas.