THE BEHAVIORAL BASIS OF LARVAL RECRUITMENT IN THE CRABCALLINECTES SAPIDUSRATHBUN: A LABORATORY INVESTIGATION OF ONTOGENETIC CHANGES IN GEOTAXIS AND BAROKINESIS

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Abstract
1. The first zoeal stage of Callinectes sapidus shows negative geotaxis unaffected by salinity changes of 5‰; high barokinesis at pressure increments above 1 atm; an increase in swimming rate with a salinity increase; and maintenance of swimming rate as temperature drops. 2. Stage IV larvae show both positive and negative geotaxis. As salinity drops, positive geotaxis prevails; as it increases negative geotaxis prevails. Stage IV larvae show a tendency to reduce swimming rate as pressure increases, as temperature drops, and as they become acclimated to higher salinities. 3. Stage VII larvae show positive geotaxis and reduced swimming rate in response to increased pressure, reduced temperature, and as they are acclimated to increased salinity. 4. Between hatching and the seventh (terminal) zoeal stage, passive sinking rate increases 3.2-fold, while swimming rate increases 4.4-fold. 5. These responses to environmental stimuli produce a pattern of early stages moving to surface waters and later stages to deeper waters. 6. Because of characteristic circulation in lower estuarine and coastal marine systems, this pattern of vertical distribution could provide a mechanism for exchange of larvae between the estuary and the coastal marine environment. 7. In stratified estuaries, offshore recruitment may significantly influence population dynamics in C. sapidus.