COVER-SEEKING BEHAVIOR AND SHELTER USE BY JUVENILE AND ADULT CRAYFISH, PROCAMBARUS CLARKII: POTENTIAL IMPORTANCE IN SPECIES INVASION

Abstract

Cover-seeking behavior of juvenile and adult crayfish, Procambarus clarkii, was examined in relation to the importance of darkness (shadow) and thigmotactic cues. Crayfish were observed individually in small aquaria 5 times per day, with at least 30 min between observations, for a 3-day period. Their positions were recorded as either within or outside shelter(s) provided. Experiment Ia presented crayfish with a choice between a clear thigmotactic shelter or open area. Adults were observed in the open area significantly more than in the shelter. Juveniles were also observed in the open area more often, but the difference was not statistically significant. Experiment Ib presented crayfish with a choice between a dark thigmotactic shelter and open area. Adults were observed more often in the open area, but the difference was not statistically significant. Juveniles were observed in the dark thigmotactic shelter significantly more often than in the open area. In Experiment II, crayfish were given a simultaneous choice among a clear thigmotactic shelter, a dark thigmotactic shelter, and open area. Adults were observed in both open area and dark thigmotactic shelter significantly more often than in the clear thigmotactic shelter. Juveniles were observed in the dark thigmotactic shelter significantly more often than in the open area and were never observed in the clear shelter. For Experiment III, crayfish were given a simultaneous choice among a dark reduced-thigmotactic shelter, a clear thigmotactic shelter, and open area. Adults chose the dark reduced-thigmotactic shelter significantly more often than the clear thigmotactic shelter, but not significantly more often than the open area. Juveniles chose the dark reduced-thigmotactic shelter significantly more often than either the open area or the clear thigmotactic shelter. Experiment IV gave crayfish a choice among a dark reduced-thigmotactic shelter, a dark thigmotactic shelter, and open area. Adults chose the dark reduced-thigmotactic shelter significantly more often. Juveniles chose the dark thigmotactic shelter significantly more often than the dark reduced-thigmotactic shelter, but not significantly more often than the open area. Darkness appears to be the controlling factor in the cover-seeking behavior of both juvenile and adult P. clarkii. The preferential use of larger shelters by adult P clarkii could reduce the limiting effects of shelter availability and might reduce competition for shelter between adults and juveniles, increasing juvenile recruitment. Differences observed in shelter use between adult crayfishes, P. clarkii and 0. rusticus, which prefer the same shelter as juveniles, may give P. clarkii an advantage over 0. rusticus in a species invasion.