Effects of chemical cues on visual orientation of juvenile blue crabs, Callinectes sapidus (Rathbun)

Stage I crabs of Callinectes sapidus occur in beds of submerged vegetation in estuarine nursery areas. After reaching the IV-V instars, juveniles leave nursery habitats and disperse throughout estuaries. This study tested the hypothesis that I and IV-V stage crabs have different behavioral responses to visual targets in the presence of chemical cues. Orientation to solid (black) and vertically striped (black and white) rectangular targets subtending different visual angles (20° to 350°) as viewed by the crabs was tested in a circular arena in the presence of chemical cues from Offshore water (control), and odor from estuarine aquatic vegetation, and predators (estuarine chemical cues). In the presence of Offshore water Stage I crabs oriented away from almost all solid targets, which was interpreted as an escape response for predator avoidance. Exposure to all estuarine chemical cues dramatically changed their behavior, as they displayed an alarm response, in which they did not orient to visual cues and their predominant behavior was to remain immobile. Stages IV-V crabs were very responsive to solid targets, as they generally swam away from the 30° and 90° targets and toward the 270° solid targets in all water types. Responses of all stage crabs tested to striped targets were more diverse. Stage I crabs generally did not orient to striped targets in any odor environment. In contrast, Stages IV-V crab responses to striped targets varied with the odor type. Thus, the hypothesis was supported because there was an ontogenetic change in orientation to visual cues. Subtle changes in orientation upon exposure to chemical cues (e.g. aquatic vegetation versus predator odor) were not evident. Crabs appeared to have two sets of behavioral responses. They showed an escape response in Offshore water and a combination of escape and alarm responses in the presence of chemical cues from estuarine nursery areas. © 2001 Elsevier Science B.V. All rights reserved.

Duke Scholars

Author Richard B. Forward Marine Science and Conservation

Author Daniel Rittschof Marine Science and Conservation