EFFECTS OF LIMB AUTOTOMY AND TETHERING ON JUVENILE BLUE-CRAB SURVIVALFROM CANNIBALISM

High frequencies of limb loss (18 to 39%) in blue crab Callinectes sap idus Rathbun populations over broad temporal and spatial scales sugges t that the autotomy response is an important escape mechanism. Limb lo ss, however, may increase vulnerability of prey in future encounters w ith predators. If individual survival is reduced significantly and inj ury frequency in the population is density-dependent, such nonlethal i njury could affect population size. Annual frequencies of limb loss we re positively correlated to blue crab abundances in the Rhode River, M aryland, USA, between 1986 and 1989, but results of open-field tetheri ng experiments indicated that, overall, missing limbs did not increase juvenile vulnerability to predators. Limitations imposed by the tethe r on normal escape behavior, however, may have masked real survival di fferences among limb-loss treatments. To test for interactive effects of limb loss and tethering on survival from predation, I conducted a s et of field experiments in 10 m(2) enclosures, using adult blue crabs as predators and intact and injured (missing 1 or 4 limbs), tethered a nd untethered juvenile conspecifics as prey. A second experiment, cond ucted in small wading pools, tested the impact of limb loss on escape speed and direction of juvenile blue crabs. Results of enclosure exper iments demonstrated that: (1) under typical field conditions and crab densities, larger conspecifics do inflict lethal and nonlethal injury on juveniles; and (2) in encounters with predators, prior limb loss do es not handicap crabs if escape is possible (untethered treatments), b ut does impose a defensive cost if escape is restricted (tethered trea tments). In addition, survivorship patterns suggest that prey missing multiple limbs altered their activity patterns to decrease vulnerabili ty. In wading pools, limb loss altered escape speed and direction, alt hough effects varied depending on the type and number of missing Limbs . Together, these experiments indicate that prior Limb loss can have c omplex effects on escape effectiveness, defensive ability, and anti-pr edator behavior. They also suggest that, despite density-dependence, p rior limb loss does not reduce blue crab fitness sufficiently to regul ate population size.