Date of Award

Spring 1996

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ocean & Earth Sciences

Committee Director

John R. McConaugha

Committee Member

Mark J. Butler IV

Committee Member

Richard B. Forward, Jr.

Committee Member

Anthony J. Provenzano

Abstract

Most research on the early life history of the blue crab, Callinectes sapidus, has been conducted in large partially stratified estuaries such as the Chesapeake Bay. In contrast, little is known about the recruitment dynamics or habitat requirements of blue crab postlarvae (megalopae) in shallow well-mixed lagoonal systems that make up a considerable part of the species' range. In Virginia's coastal lagoons, planktonic blue crab megalopae are most abundant at night on flooding tides, and are not abundant during the daytime or on ebbing tides. This appears to enhance retention within the lagoons, despite the short residence time of water in the system.

Seagrasses are largely absent from the lagoons and megalopae use benthic macroalgae as a settlement habitat. Laboratory experiments demonstrate that macroalgae is an effective refuge from predation for newly settled megalopae. Megalopae appear to recognize waterborne cues in the lagoon that enhance recruitment by initiating premolt and reducing the time spent in the megalopal stage within the lagoons. Intermolt megalopae exposed to lagoon water quickly advance to premolt and molt to the juvenile stage in approximately 2 days. In contrast, intermolt megalopae held in shore waters appear to delay metamorphosis until estuarine cues are recognized.

The results of this study illustrate some of the adaptations that aid blue crab megalopae in the recruitment to coastal habitats. These adaptations include the ability to recognize and distinguish between inshore and offshore waters, the ability to modify swimming behavior in inshore waters to effect landward transport, and the ability to utilize alternative settlement substrates in the absence of seagrasses.

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DOI

10.25777/cqh6-qv32

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