Testing a selective tidal-stream transport model: Observations of female blue crab (Callinectes sapidus) vertical migration during the spawning season
Female blue crabs, Callinectes sapidus, mate in estuaries and undergo a seaward spawning migration to release larvae. According to the prevailing model, females with mature embryos use nocturnal ebb-tide transport (ETT) to move seaward, release larvae, and then reverse to nocturnal flood-tide transport (FTT) to move back into the estuary. We tested this model by examining the vertical migratory behavior of ovigerous and post-larval release female crabs. Simultaneous physical-biological data were collected for 38 d during Aug 2002-Sep 2002 in Bogue Sound, North Carolina. Crab water-column positions were determined with miniature internally recording pressure sensors. Local current and water properties were measured, and crab vertical migration times relative to observed currents were used to determine ETT and FTT behavior. Surface censuses of free-swimming crabs on 19 nocturnal ebbs were used to complement the intensive studies of individual crabs. The study found that (1) the pressure sensors had a measurable but small effect on swimming, (2) females migrated during day and night ebb tides, (3) females used ETT throughout embryo development, (4) ETT corresponded to the rate of decrease in water level (hydrostatic pressure), (5) larvae were released at high tide or when water level was falling, often within several hours of sunrise, and (6) post-larval release females continued ETT and did not switch to FTT. Thus, the data did not support the prevailing ETT-FTT reversal model. Rather, females continue ETT into coastal areas, releasing subsequent clutches farther seaward, which increases the potential for successful larval transport to favorable offshore developmental areas.
Hench, JL; Forward, RB; Carr, SD; Rittschof, D; Luettich, RA
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