Orientation of juvenile blue crabs, Callinectes sapidus Rathbun, to currents, chemicals, and visual cues
Postlarvae of the blue crab, Callinectes sapidus, settle and metamorphose in beds of submerged vegetation in estuarine nursery, areas. They remain there until crab stage IV or V, which disperses throughout estuaries. The study considered orientation of Stage IV-V crabs to chemical and visual cues in the presence of current flow. Crabs were tested in a horizontal rectangular chamber that had test waters entering the ends of the chamber and exiting at the center. An orientation response occurred if crabs moved from a center release site to the end of the chamber. Test waters were "Offshore" odor water and estuarine odors (estuarine water, habitat odor from salt marsh cord grass and oysters, predation odors from mud crabs, and predation event odors from crushed conspecifics). In apparent darkness (red light), crabs did not orient to flow (flow rates = 0-30 ml min-1; current speeds = 0-6.2 cm s-1) but moved away from all estuarine odors. When a visual target representing a predator was placed at one end of the chamber, the crabs failed to orient to the target in Offshore odor water. However, when Offshore odor water was paired with any estuarine odor, the crabs moved away from the visual target regardless of its location. These results indicate there is a hierarchy of responses to flow, odors, and visual cues. Subtle changes in behavior with odor type were not evident. Thus, crabs have different behavior in Offshore odor water and in estuarine odor waters.
Díaz, H; Orihuela, B; Forward, RB; Rittschof, D
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