An emerging body of literature points to post-settlement, planktonic dispersal as a key
determinant of distribution and abundance patterns of aquatic organisms, yet little is known about
mechanisms inducing such dispersal. Recent evidence suggests that early juvenile blue crabs
(Callinectes sapidus Rathbun) may use planktonic emigration as a means of post-settlement
dispersal. The goal of this study was to identify mechanisms inducing post-settlement, planktonic
dispersal of early juvenile blue crabs. A combination of field mark–recapture experiments in large
seagrass beds within a 233 km region near Oregon Inlet, North Carolina, USA, and a series of
laboratory flume experiments examined the effects of day vs. night, crab size (first-second juvenile
benthic instars: J1–J2 vs. third–fifth juvenile benthic instars: J3–J5), crab density and current
speed on planktonic dispersal of early juvenile blue crabs. Transport of dead crabs in the flume
experiment identified that planktonic dispersal was an active behavioral response rather than a
passive response to increasing current speed. The experimental results demonstrated that
planktonic dispersal can range from 4 to 18% under medium to high flow conditions. Planktonic
dispersal of juvenile crabs is (1) an active behavioral response, (2) increased significantly with
21 current speeds above 20 cm s , and (3) was higher for relatively large (J3–J5) than small (J1–J2)
instars. There was a non-significant trend towards greater dispersal at night than during the day in
the field experiment, and no effect of crab density on dispersal in the flume experiment. The
results from this study highlight the need to consider mechanisms inducing post-settlement,
planktonic dispersal when attempting to understand and predict recruitment and population
dynamics of aquatic organisms, as well as when linking hydrodynamics, animal behavior and
planktonic dispersal. Ó 2001 Elsevier Science B.V. All rights reserved.